Category Archives: Ceramics ดินเผา

The Square Wheel, A structural look at Innovation in the ceramic arts

Where do ideas like The square potter’s wheel, and a Flame throwing pipe organ come from. An Outline for a talk at NCECA 2027. This wriiten set of nots should be considered a work in progress rather than anything finished.

An understanding of undergraduate critiques of the minimalist sculpture type known a s functional pottery. Does the rim look like it just happened or was it made that it is with intent. Is it loose throwing or sloppy. Was it sloppy with intent? or better does it appear to be sloppy with intent? Once it looks intentional there meaning seems there to discern.
What parts of the design have not been considered? Or what parts look as if they have not been considered.

New ideas, innovation happens in the same space,it flows the space of idea not yet considered. In our minds it is easy to segment the realms of ideas not yet considered but in some sense they are all the same. Just the same lets segenent Lets go through some of them as the relate to clay.
Tools
Tools not yet considered as appropriate for the use you will use them for. Examples
Sand Blaster used by Kurt Weiser
Air Chisel on glass by Janusz Walentynowicz
CinvaRam Brick Press by Louis Katz
Unusual hand tools. Student Exercise.

Materials

Materials discarded as impractical or not yet considered for the use you put them to.
Portland Cement glazes
Calcium Chloride for surface decoration
Gerstley Borate as clay ingredient to promote scumming
Chunky Copper wire Oxide
Corn
Sewage Treatment Plant Ash
Discarded sludge from granite countertop cutting.
USe of Cobalt Oxide as a flux. (Ceramic MAterials Workshop)
Use of Manganese Dioxide as a flux (Baslat Ware Wedgewood)

Techniques that won’t work.
Clay on welded wire fencing
Slipcast Glass
Difficult forms

Glaze faults
Sperry platters
Crawled Shino
My student’s teapot

Absurd Amalgams.
Cutting molds with saws rather than making separate pieces. Who is the person doing this today? Is this really just a different tool application?
Urban Teapots
Is this new? Shang Dynasty Bronzes.

New ways to do old things.
Walk around the pot rather than spin the pot. THis is really an old way to do it.
Make Chrome thin Pinks with Zinc (Ceramic Materials Workshop research)

Inbetweens happen between words and concepts. There is no hard like between blue and green yet we treat them as if they are distinct. Many of the most interesting colors occur in the area where these colors approach these verbal distinctions. People that think as if colors are distinct live outside of subtle use.

But the line between function and non function is a similar line. Something pleasurable to look at serves a function. In my Uncle Bernie’s verbiage, designed to poke fun at contemporary abstract sculpture, sculpture modulates space. Paintings act as decorations for walls. The function of art is as objects of contemplation, avenues for expression. It is this line, and how we define it in Ceramics, that was the first place where I see idea as the realm where I started to innovate. What is function? What functions are we forgetting about? What do we mean by it.

What is Ceramics? Most will tell you its a class of materials. But even then it depends on who you ask. A chemist will tell you “Metal Oxides”,  an engineer will tell you materials to hold or withstand  high heat, an NCECAist might tell. you clay and glazes. Glass they might see as a grey area?

Me? I sufferer from Meglomania Ceramica, I claim it all, graphite, granite, portland cement, glass, silica gels, and yes clay.
But Ceramics is also a way or group of ways of looking at design, ways of working, a history or historys.
You, You are Ceramics. Ceramics is a community or maybe communities. I call members of this community Clayers,
How you look at Ceramics influences how you see what you can call ceramics. How you define function limits what you call functional Ceramics. Even people who are serious about making functional pottery understand this. Mark Hewitts titling a jar “umbrella holders” is a clear sign of this.

As an exercise, perhaps in absurdity, but certainly as a way to grow, to come to grips with the illusional order word definitions inflict on the world, I inflate definitions until they encompass as much of reality as I can muster. I truly am tired of the hierarchy in the arts. I refer to painting as ceramic and other pigments stuck in place by a binder. This converts those cave paintings in Lascaux and elsewhere from the craft of painting to the Art of Ceramics. The cave walls, rock, are ceramics too. Lets make sure that the art historians get their terminology straight. Shall we?

Better get to the wheel. What parts of the wheel to we just accept and live with? The stable axis. Some of us do understand that steady speed is not so necessary, that is if we throw for long on a Leach Wheel or make big things on a kick wheel. Steady speed is not needed but spinning on a stable axis never gets questioned.

Kurt

รายงานเรื่องครก

2534 24 มิถุนายน เวลา 15:00 น. วันก่อนวันแต่งงาน ผมไปที่ร้านขายของชำเอเชีย ผมซื้อครกและสากแบบไทย มีการตกแต่งด้วยน้ำดินสี ( slip) รูปทรงของมันไม่สมมาตรเสียทีเดียว ผิวด้านนอกเคลือบด้วยสีน้ำผึ้ง ( Honey colored glaze over the slip) มี ขี้เถ้าไม้ติดอยู่กับเคลือบนั้น มันคือมินเก (Mingei) ของแท้ Mingei เป็นคำภาษาญี่ปุ่น ซึ่งแปลเป็นภาษาอังกฤษว่า “งานหัตถกรรมพื้นบ้าน” (folk craft)คำนี้ถูกใช้ในลักษณะที่แยกออกจากศิลปะอย่างชัดเจนคำนี้ถูกใช้ในลักษณะที่แยกออกจากศิลปะอย่างชัดเจน “มิงเกอิ” (Mingei 民芸) หมายถึงสิ่งที่เรียนรู้จากพ่อแม่หรือช่างฝีมือคนอื่น ไม่ใช่เรียนรู้จากโรงเรียนหรือวิทยาลัย ครกมีสติกเกอร์เล็กๆ ติดอยู่ว่า “Made in Thailand” ตอนนั้นผมไม่รู้จักคนไทยเลย ยังไม่สนใจประเทศไทย แต่คิดว่าครกนั้นสวยงาม

มันเป็นของขวัญสำหรับเกลและตัวผมเองในวันก่อนที่เราจะแต่งงานกัน มะละกอบ็อกบ็อก
ครกนั้นมาจากจังหวัดราชบุรี ผมคิดว่ามันพิเศษ สำหรับคนไทยมันเป็นเรื่องธรรมด ผมมีความสนใจในสิ่งเรียบง่าย สิ่งที่พบเห็นได้ในชีวิตประจำวัน สิ่งของราคาไม่แพง และงานหัตถกรรมพื้นบ้านอยู่แล้ว มันคือความงดงามแห่งความพอเพียง มันเป็นครกและสากแบบไทยชุดแรกที่ผมเคยเห็น และเป็นเพียงชุดเดียวที่ฉันเคยเห็นจนกระทั่งได้มาเยือนประเทศไทยในปี  2531ค.ศ. 1988 . แต่ที่ร้านมีโอ่งมังกรอยู่หลาย
นี่คือเรื่องราวของถนนหนทางและการคมนาคมขนส่ง ค่าจ้างและแรงงานหลายสิ่งในเรียงความนี้เป็นเพียงความคิด แนวคิด และทฤษฎีเท่านั้น ในช่วงเวลาที่เรากลับมายังสหรัฐอเมริกาเมื่อปี ค.ศ. 1989 นั้น มีครกจากปากเกร็ดวางจำหน่ายอยู่ในร้านขายของชำเอเชีย ค่าแรง ดินเหนียว และฟืนยังคงมีราคาถูกบนเกาะเกร็ด ฉันคิดว่าค่าแรงในราชบุรีเริ่มสูงขึ้น ในขณะที่พวกเขาส่งออกโอ่งมังกรไปทั่วโลก แต่ไม่นานหลังจากกลับมายังสหรัฐอเมริกา ก็เริ่มมีการเปลี่ยนมาใช้ครกดินเผาด่านเกวียนแทนครกดินเผาเกาะเกร็ด ตอนที่ฉันไปเยือนเกาะแห่งนั้น ผู้คนบอกว่าที่ดินมีราคาแพง ดินเหนียวก็แพง เชื้อเพลิงก็แพง แต่ปูนก่อกลับมีราคาถูก ภายในปี ค.ศ. ~1994 การผลิตครกบนเกาะเกร็ดได้ยุติลงเป็นส่วนใหญ่ ส่วนใหญ่ที่ผมเห็นในสหรัฐอเมริกาคือครกจากด่านเกวียนและอุบลราชธานี ในปี ค.ศ. 1989 สภาพถนนได้รับการปรับปรุงให้ดีขึ้นมาก และต้นทุนค่าแรงในบริเวณใกล้กรุงเทพฯ ก็ปรับตัวสูงขึ้น
ช่วงปี ค.ศ. 1994–1997 ถือเป็นยุคทองของ Dankwian Ceramics โดยมีการส่งออกสินค้าประเภทเครื่องปั้นดินเผาในปริมาณมากเต็มตู้คอนเทนเนอร์อยู่หลายครั้งต่อสัปดาห์ครกจากด่านเกวียนมีราคาถูกเกินไป ในขณะที่ค่าแรงนั้นมีมูลค่าสูง ด่านเกวียนจึงเริ่มจำหน่ายครกที่ผลิตในจังหวัดอุบลราชธานี  อุบลราชธานีกลายเป็นแหล่งจำหน่ายครกและสากในราคาประหยัด ทุกวันนี้พวกเขาก็ยังคงเป็นสถานที่ที่ใช่ ก็เป็นเรื่องเดิมๆ นั่นแหละ ถนนหนทางดีขึ้น และค่าแรงในด่านเกวียนก็แพงขึ้น แต่อุบลพ็อตเทอรี่ส์ก็มีประสิทธิภาพสูงขึ้นมากเช่นกัน

ในปี ค.ศ. 1989 เกิดน้ำท่วมครั้งใหญ่ในภาคใต้ของประเทศไทย และมีเหตุดินถล่ม ส่งผลให้มีผู้เสียชีวิตจำนวนมาก เหตุการณ์ดินถล่มมีสาเหตุมาจากการตัดไม้ทำลายป่า รัฐบาลจึงสั่งระงับการตัดไม้ทั้งหมด ฟืนมีราคาแพงมาก
ที่ด่านเกวียน พวกเขาเริ่มเผายางรถยนต์เก่าและทดลองใช้น้ำมันเครื่องที่ผ่านการใช้งานแล้ว
ผู้ใหญ่บ้านหมู่บ้านเครื่องปั้นดินเผาในอุบลฯถามผมว่าพวกเขาจะเติมอะไรลงไปในดินเหนียวของอุบลฯ ได้บ้าง เพื่อให้สามารถเผาที่อุณหภูมิต่ำลงได้ ฉันบอกให้ทำเคลือบเงา เกลือ ภาษาไทยของฉันแย่มาก พวกเขาพูดว่า “เกลือไม่เผา” แต่ผู้ใหญ่บ้านมีหนังสือชื่อ “Ceramics: A Potter’s Handbook” ของ Glen Nelson ซึ่งมีการกล่าวถึงการเคลือบเกลือ (salt glaze)
ตอนที่ผมกลับมาที่ด่านเกวียน วิศวกรชาวไทยคนหนึ่งแวะเข้ามาหา เราได้พูดคุยกันเรื่องเชื้อเพลิงและหมู่บ้านด่านเกวียน จากนั้นเราก็คุยกันถึงเรื่องอุบลฯฉันเล่าเรื่องการเคลือบด้วยเกลือ (salt glaze) ให้เขาฟัง แล้วเขาก็บอกว่าบางทีเขาอาจจะอธิบายเรื่องนี้ให้พวกเขาฟังได้ การเคลือบด้วยเกลือทำให้ได้ผิวหน้าที่แข็งแกร่งขึ้นที่อุณหภูมิต่ำกว่า ไม่กี่ปีหลังจากกลับมายังสหรัฐอเมริกา ก็เริ่มมีครกเคลือบเกลือจากอุบลราชธานีวางจำหน่ายตามร้านขายสินค้าเอเชีย

คุณภาพ: ด้านภาพและด้านเทคนิค
รสชาติดี แต่ก้นบาง ปัจจุบัน ครกที่มีคุณภาพดีที่สุดมาจากบ้านโพนบก อำเภอโพนพิสัย หรือจากอำเภอท่าอุเทน จังหวัดนครพนม 
แม่ค้ามืออาชีพส่วนใหญ่ที่ขายส้มตำตามริมทางมักใช้ครกไม้หรือไม่ก็ครกที่ผลิตในอำเภอโพนพิสัย 
โดยทั่วไปแล้ว นครกที่จุดไฟด้วยความร้อนสูงกว่าจะใช้งานได้นานกว่า ฉันคิดว่าเหตุผลส่วนหนึ่งที่ทำให้ครกจากโพนพิสัยมีคุณภาพดีกว่า ก็เพราะมีฟืนมากกว่า ในความคิดของผมครกที่มีคุณภาพดีที่สุดคือครกจากเกาะเกร็ด เพราะผ่านการเผาด้วยความร้อนสูงมาก อีกทั้งยังมีขอบที่หนาและหนักที่สุด รวมถึง ก้นครกที่หนาที่สุดด้วย ครกราชบุรีก็มีเนื้อดินที่แข็งแกร่งเช่นเดียวกัน แต่ส่วนขอบปากและฐานนั้นไม่ได้หนาหนักเท่ากับครกเกาะเกร็ด ครกจากท่าอุเทนทำขึ้นโดยใช้แม่พิมพ์ ซึ่งรูปทรงแบบนี้ไม่ใช่สไตล์ที่ฉันชอบเท่าไรนัก แต่เนื้อดินนั้นสวยงามทีเดียว
หากต้องการส้มตำรสเลิศ คุณต้องใช้ครกจากด่านเกวียน

 




 







 

When You Know Stuff

“When you know stuff you can do stuff”. This is a quote from a very prolific ham radio homebrewer, Pete Juliana, callsign N6QW. It is possible that he has built more homemade transceivers of unique designs than anyone else.

In high school I read a lot of books and skimmed dozens of others. In total I believe that this was more than 100 books. Most were from The Detroit Public Library but also included my local library, my school library, and a bunch of books I bought with money earned from singing.

I tended towards books that were technical but not at the level of Engineering. Although I did take some engineering books home to look through.

This voracious appetite for ceramic reading did not stop until the late 1970’s. When at the Archie Bray Foundation visiting I read through everything I could in the library and skimmed many other books. What I learned in that library helped me be successful at many things a few of which I can track.

But it is not just books that have value to read. Instruction manuals for kilns have a lot of important information. The Orton Foundations literature on temperature, cones, and other measurement devices is very helpful. Omega Engineering used to have a product application book that had a bunch of basic knowledge on thermocouples that I have found useful.

The AP Green book on bricks was a great read. It informed how I built kiln walls. There was something called The Gas Consumption Handbook that I enjoyed.

These days of instant information people love to ask questions online. The amount of laziness and lack of reading is palpable. Page 32 of the latest Skutt Manual has the Error codes. Before you ask a question here you should at least have the courtesy to check the manual.

This does not mean that I won’t answer these questions that should be easy to find answers to. Nor does it mean that sometimes things don’t fall through the crack of our acquisition of knowledge.

But when you know stuff you can do stuff. Most of my new ideas require knowledge in order for me to evaluate them and then to implement them. In Studio Ceramics a good place to start is a basic textbook as it can provide a framework for further knowledge and gets you started with a broad understanding. I suggest Nelson’s “Ceramics: A Potter’s Handbook” any edition. The pictures are better in the newer additions. They can be found for less than $10.




WhatsInaCup

What is in a cup? [still writing]
An essay about a single cup,stoneware, a touchstone, vessel, works with coffee, tea, jelly beans. 

I have been using a cup that I made in Thailand since 1988. This is an essay about the areas in my life it touchs, the thoughts that are tangent to its exterior, its place in my life. 

I suppose that this starts in about 1972 when I first signed up for ceramics classes in High  School. 
I walked into school as 11th grade was about to start and got in a line. At the head of the line I was given my schedule. I had selected classes as the previous year was ending. These included Electronics, Choir, Trigonometry, I am not sure what else. I was given the schedule and looked at it. I told the teacher behind the desk, ” I can’t take this Trigonometry class”. We went back and forth with him telling me that he could not change it, getting mad when I insisted. Then I let him know that the teacher was my mother. He said, Come back here, lets see what we can do. I remember that the schedule after changing the Trigonometry class was really limited. I needed a different class for 7th hour. I tried Metals shop, Drafting, Hebrew language, Physics, Photo, probably others. There was something left called Ceramics. I think that I had to ask what it was. That is how I got started. 
We did some American Raku firing during the class. When you do this you get surfaces that are outside your direct control. They have an air of naturalness at times. By this time in the semester I was reading books about ceramics every week, lots of books. A few were about this technique, Raku.
Raku, at least in some ways, revolved around a Japanese aesthetic principal, wabi.  Wabi describes an appreciation of the worn, the old, the imperfect, in some ways just nature. While I have been told that it is Zen in origin, I think the real origin is closer to Taoism.  In my first year in college I took a course from  Dr. Walter Spink who described a person who was perfectly in tune with the Tao, the nature of nature. This person walked down to the bridge over the raging flood in a rocky mountain stream, disrobed waited a few seconds and jumped in. Perfectly in tune with the Tao, he washed up a bit down stream perfectly clean and walked back up to get his clothes. He understood the way, the way of the world, and without much effort could chose just the time and place to jump in and get washed out. Images of streams and rocks are seen as symbolic of The Tao. The ideas and practice of Taoism predate the Buddhism and particularly Zen by many centuries. However, Wabi is attached with Zen. I am not an expert in either, nor a practitioner.  
Raku is really the granted title of a person who made teabowls. It then named the process and style of their making. The title is hereditary. The current holder is Raku Kichizaemon XVI. I met  Raku XV at The Archie Bray Foundation. I found it not that remarkable a time except that  I found it ironic that the slide projector we were using for his slide show caught fire. 
Making work in this genre that really does it for me is difficult. The skill and sensitivity is something I cannot quite grasp. Excellence always involves the intangible, but for teabowls it often seems further from my grasp.  I really started to appreciate the aesthetic early and in high school built a wood burning raku kiln in my backyard. 
I ended up in undergraduate school in Kansas City, Missouri at The Kansas City Art Institute. The department head there, Ken Ferguson, was enthralled by Wabi Sabi. The museum next door, The Nelson Atkins museum always had a few pieces of Japanese teaware on display. Between Fergusons interest, the pots at the Nelson and the general tone of American Studio Pottery at the time we were all sucked into the aesthetic.  
In the 1970’s there was a strong “back to nature” cultural push. The organic foods movement got a big boost. Gas crises helped create a low energy mindset. Home grown and home made, local production and consumption all had strong cultural support. Natural looking fired surfaces were a rage, and in some ways still are.

A group of potters associated with the late Warren Mackenzie who was an apprentice of Bernard Leach taught at Minnesota State University and a group of potters gathered in the area. Many of them were dedicated to natural surfaces in their work and used the kiln as the creative instrument to make the surfaces. They fired with techniques now know as “atmospheric firing techniques” but not raku. Raku makes good ceremonial ware, but is not a good choice for daily use. The techniques used were wood firing, salt firing, a kind of firing called residual salt, and an offshoot of salt firing, soda firing. These techniques were used at high temperatures with non-porcelaineous clays to give the works rough natural surfaces. 

Bernard Leach worked in Japan with a potter Shoji Hamada. Along with Soetsu Yanagi they were interested in what has been translated often as Folk Craft or in Japanese, Mingei. In school, Ken Ferguson was standing behind Gail and said, “I wonder how you could combine Mingei with Minnesota. Concentrating on something else Gail said, “Minegeisota”. Clearly already having this word at hand but now having someone else to blame for it Ferguson tried to use it as a putdown to these potters. Instead of it being a putdown, they embraced it. What had been known as the Warren Mackenzie style or school of pottery making became known as The Mingeisota School. 

Prior to these names, atmospheric firing, Mingeisota, or knowing the phrase Wabi Sabi, I was already enthralled. I preferred wearing jeans until thread bare. The same is true of shirts. The use, the wear, the rips, all tell a story. The story “new” tells is a false cloak of respectability. Respectable cloths do not impact the respectability of those wearing them. You are how you look is only an “ism” an illness of an imperfect society whose focus is on trivialities rather than realities. 

But when Yanagi, Hamada and Leach talked about Mingei, they were talking about ceramics outside of schools, outside of galleries, indigeneous, humble. I do not think that they were even at the beginning talking about what they made, it was too expensive. They were talking local production for local use. 

Repair rather than replace is either the mark of people without much cash, or a sign of someone who values the natural of materials, the work of hands, the environment, or economy.  People like this have values. New clothing is an affectation. I find it hard to label its draw to some as a value. 

The affectation of the worship of the new, is in some a desire to show that they earn money. This desire is understandable as our language continually mixes up values and value or qualities with quantities. I am reminded of Lung Gaeow, an old friend in Thailand with little money or possession but a great human full of humor, compassion, and hard work. 

While in school in Kansas City we were given an opportunity to order books from Kodansha Publishing on kilns in Japan and their wares. There was one book for each pottery village, sometimes two different ones. These books was about  18 inches by 12 inches with huge high quality color photographs and cost less than $5 each. A Japanese student, Akio Takamori who the community sorely misses, picked up the books and shipped them. These books introduced us to Japanese potteries, “The Six Ancient Kilns” and many others were included in these series of about 50 books. I fell in love with Bizen and Shigaraki, although there were countless others it seemed that also held my interest. 

Bizenyaki, the Bizen potteries, fire much of their work to just the temperature that the clay starts to be vitrious, but can still maintain the orange color if protected from the flame and ash. How the kilns are stacked in Bizen became the primary decorative technique leaving some areas orange, some brown. Stacking with rice straw left markings from the alkali metals in the straw.  

In graduate school a fellow student, from Thailand showed me slide images of a pottery in NE Thailand called Dankwian. The pots were almost exclusviely 20 gallon water storage jars, wood fired, no glaze, fired to about cone 7, a lot like Bizen pots. But these had never been snarfed up as teaware. They were intended for humble use. Most pots like this were long gone in Japan. 

The graduate student, now retired Professor Poonarat Pichayapaiboon, and I took courses together. His English was spotty so as I helped him with English he taught me a bit of Thai. A few years after graduate school I heard that there was a Thai potter visiting the Archie Bray Foundation. I walked up, and in Thai said, “Hello! Where is the bathroom”. She pointed. I then asked what I though meant, ” Do you know of the village of Dankwian?” Not really meaning that she responded in English “What do you mean?”. Turns out she owned a pottery there.  This is what prompted the Thai Fulbright. 

Burners, Atmospheric, Considerations, Addendum on Wood

Kiln Burner Painting

Venturi Burner by Louis Katz , all-weather paint stick on plywood, torched.

Nothing in this post should be considered safety information. A lot of it is just what I think, not having read it anywhere in a format I could really understand. Other information I am consolidating.

Atmospheric burners are not understood particularly well by ceramic artists. I am going to try and clarify some things about them. I have not found any wonderful texts about them, most of what I know has been gleaned from catalogs that used to provide much more information than can be found now. While this is almost exclusively Eclipse® and Pyronics® catalogs others have entered into the mix.  To simplify things I am only going to consider Natural gas, an impure methane that is generally delivered through pipes to homes and businesses. I live in the US. So its possible that something I say will only be applicable here,,, but I can’t think what that would be.

Entrained Air
An atmospheric burner with a venturi tube is a device whose function is to efficiently use the kinetic energy of gas coming out of an orifice to carry air with it. The air that it carries through the burner is called “entrained air” also “primary air”. 

Orifice
The orifice that the gas flows out of is called the orifice, sort of a truism. The size of the orifice and the pressure the gas is under determines how many BTUs, calories, or cubic feet of gas are flowing into the burner. Orifices that are properly made and drilled create less turbulence when the gas exits the orifice and prevents loss of kinetic energy. This consequently increases the amount of air that will or can be entrained. We will discuss this further below in several places.

Primary Air
Primary air is the air entrained in the burner. The air coming into the kiln around the end of the burner is secondary air.  I guess much of this is redundant. It seemed needed. 

Flame Retention Ring
These are devices on the kiln end of the venturi tube whose job is to efficiently mix the gas and air, create a faster area for the mixed gas and air to flow through, and often provide a small amount of slower gas around the circumference to act as a pilot for the flame so that it will always light near the Retention Ring.  The faster speed is so that the mixed gas and air is moving out quicker than it is burning back into the burner. If the speed in the retention ring is too slow then you get back burning, burning inside the venturi tube. This creates soot and other troubles.

Methane – CH4

How Atmospheric burners, a mixer head where the orifice and air come, a venturi or straight tube, and flame retention ring, are sized.

The exact amount of oxygen (from air) needed to burn a molecule of methane, CH4, into carbon dioxide and water is CH4 +2O2 = CO2 + 2H20,, two molecules of O2. How much is this by volume or weight is not really important. But this ratio, we will call Neutral Combustion.

If it were only the gas we were concerned with then burners would be sized by the size of the gas orifice. You would not use a burner, and just pump gas into the kiln. All the air would be brought in with the chimney and the kiln would need to be kept at a higher negative pressure to do this. But there are two problems with this. One is that any leaks in the kiln will bring larger amounts of air in, and if they are not near the gas source then they will cool those areas, and keep them oxidizing more than anyone would need them to be. The second problem is that you need mixing of gas and air.  Gas heated in the absence of enough oxygen will produce soot, pure or nearly pure carbon. [This is hard on people contributing to heart disease, lung disease and cancer along with particulate pollution and other environmental effects.] Soot can be very slow to burn. There may be times when you want soot such as carbon trapping glazes but for the most part it is usually just wasted fuel. Assuming that the mixing of gas and air before heating is good, then this happens when the oxygen is less than 1/2 of the amount needed. CH4+O2 = C +2 H2O. In general this is a good way to waste fuel. In small gas kilns some of this burns in the chimney, but some does not. Unfortunately Carbon does not reduce carbon dioxide to monoxide, at least not easily as far as I know. I suspect that if you heat carbon and carbon dioxide hot enough you will get carbon monoxide forming,,, but I do not know enough to be sure of this. Perhaps a chemist will chime in.

[I recently found a copy of a a catalog for the  now unavailable single state Low Pressure Injectors from Eclipse. It gives numbers for 30-50% entrainment. This does not fit my memory or understanding.  Eclipse Atmospheric Injectors, Bulletin 650, 1/8/2015]

The charts that I have seen for burners being sold generally state an assumed amount of entrained air. For example; These numbers may assume that some percentage of the air needed for neutral combustion will be entrained by the burner. That is, a little over 1/2 the air needed to completely burn the gas will be entrained by the burner (or mixed in at the burner tip as secondary air). You will get some CO2 from this air, but most of the carbon will leave as CO which will still burn if more air, more O2, is provided. You only need or want a little CO for reduction. Too much and your kiln will not climb in temp and you will waste time, fuel, money. Too little will be talked about under mixing a few paragraphs down. 

The rest of the air needed is supplied by secondary air coming in around the flame retention ring. The O2 in this air burns the CO into CO2.

Why do you get more BTUs with higher pressures?


Lets just say you have a cubic meter, or cubic yard if you insist, of gas. I find it easier to image this with more gas especially when it is at a very low pressure, say 1cm water column, or 1 inch water column if you prefer. The gas, coming out of the orifice will come out slowly and will have little kinetic energy in the stream. In fact it will only have the kinetic energy used to compress it. If you use way more energy to compress the gas you will also need a smaller orifice if the gas is going to come out at the same rate. But having put more energy in you get more energy out. This energy, in part transfers to the air coming into the burner, in fact this energy is what draws air into the burner. I find it easier to visualize with the idea that the gas coming out the orifice blows air out of the burner, the air then needs to be replaced so more is drawn in. High pressure, small orifice, entrains more air because there is more “blow”, more kinetic energy, in the gas. More air means that keeping to 65% of what you need for full combustion, means you can use more gas. More gas means even more kinetic energy. Higher pressures increase the capacity of the burner. However they also increase turbulence. At some point the amount entrained in the burner no longer increases much as the pressure increases. When you get to the point where the air that can be entrained drops below 65% of that needed you have reached the maximum practical pressure of the burner.  Eclipse and Pyronics used to release good charts on their burners that mostly made this clear if you studied the numbers. 

Negative pressure at the burner port.

If  kiln is hot and the damper open you can get a slight decrease in pressure at the burner port. Assuming that the burner is placed properly in relation to the port, this decrease in pressure will allow more air to be pushed (or pulled if you like) through the burner,,, . I think of this lower pressure as sucking air through the burner. [The sucking or pulling is an easier model but is not technically correct.]  Lets assume that you make those ports too big. In order to get a given volume through them you need only a little pressure difference. As they get smaller, the pressure in the ports is going to fall. This increases the capacity of the burners because it decreases the pressure at the burner head. There needs to be enough space around them for the requisite secondary air. [100%-65%=35%]. But often these ports are made too large if the goal is maximizing the capacity of the burners so that you can heat faster.

Further the flame retention ring acts in respect to the burner port similar to the gas in the burner and carries secondary air into the kiln using its kinetic energy.

Mixing

In order for the gas to burn it has to be in contact with the oxygen in the air. If it gets hot without the air it won’t burn. If it gets hot with only a little air you will get soot. The most important mixing happens before it burns, in the flame retention ring. Burners made without them have the potential to waste a lot of fuel as soot . CH4+O2 = C +2 H2O. Interestingly higher gas pressure should produce more turbulence in a given amount of time but the gases also move through the burner body quicker. I think that you end up with better mixing, but I am not sure.  It does appear that you get better mixing with the secondary air.

About 68 percent of the heat in methane is released burning it to carbon monoxide. Knowing this makes it clear why firing closer to neutral is quicker. I like to think if firing with too little air, firing in too much reduction, as being like paddling upstream with a small paddle.

Bad mixing, too little primary air, soot, once the kiln is quite hot,  can make determining if you are reducing difficult. The soot can be burning off in the flue making flame and looking like reduction. The same can happen out spyholes. You can close down one burner’s primary air and get soot, have the kiln oxidize and have flame at the spy holes (bungs) and at the flue.

While we are on it, the flame does not come out of the kiln unless there is oxygen that is not yet combined coming out as well. The flames we normally see from uncombusted gases coming out from the kiln are hollow and start where they come in contact with fresh air. Paying attention to this, especially in wood or oil kilns can save a lot of heartache and trouble.

Heat is released when all the necessities for combustion are met, heat, O2, fuel and mixing. Well I suppose they are not in the same place unless they are mixed, but that is a fine point. The sooner good mixing takes place the sooner the heat is released. Since primary air mixes at the burner, secondary air released later in the kiln chamber. Up to a point this can be used to control temp in different parts of the kiln. 

Mixing is always imperfect. As you approach neutral combustion you should assume that some parts of the kiln are in oxidation, some reduction, as well as some parts effectively neutral. Likely with methane there is always some water gas reaction. Who knows how long hydrogen can survive in a mixed atmosphere.  There is too much I don’t know.

Wood Combustion

Part of this dynamic and discussion seems very important in wood kilns, particularly long ones. “This is what I see happening.”” This seems in part more like conjecture.” I am going to encode sentences with how certain I am of them. Sentences with fairly high certainties will have one period. Sentences where I am pretty sure two periods.. Less certain, three periods… just a working theory, four…. These are of course approximate. Some things might be substantiated by reading, some by experience, some just because they make sense.

Pyrolysis of wood produces many products. At higher temperatures these include H2 (hydrogen molecules), CH4 (Methane), CO (Carbon Monoxide) , and CO2(Carbon Dioxide) and H2O (water). Charcoal becomes mostly just carbon and ash as pyrolysis progresses. As it becomes more pure it burns more and more only on the surface. 
Before coming into contact with added air, some of the methane and water is going to go through the water gas reaction, CO+ H2O = CO2 + H2  .. This does not really change what is in the mix, just the proportions of it.

So, for me the easiest to start with is the Hydrogen. It is the easiest to burn.. It has the lowest flash point and the highest affinity for oxygen of all the common products of pyrolysis.. It burns first.. Like carbon monoxide its affinity for oxygen makes it an agent for reduction. But these two ingredients appear to have different properties of reduction of glazes.. This  appears to create some of the vagaries of wood fire.

Because of hydrogen’s high affinity for oxygen and its tendancy to burn quicker and easier it is the first to leave the stream. Because of this, it often is not likely to affect the clay. It disappears too quickly by becoming water. But one of its properties differentiates it from carbon monoxide. It is more soluble in glass than carbon monoxide.. Where carbon monoxide either needs to reduce a glaze only on the surface or only before it is melted, hydrogen can effectively penetrate the surface of the glass and reduce materials after they have melted.. This appears to be the mechanism that creates the salmon colored flashing often sought in wood and soda firing.. How this relates to other mysticism relating to the miraculous Avery Kaolin I don’t know. I am certain that Alan Watts must have done a lecture on Avery…

That salmon color seems to require a small amount of volitalized alkali metal. You can get it with both potassium carbonate and sodium carbonate is vapor kilns. It is not strictly a soda color. But introduction of water into a reducing stream of gas appears to increase the amount of salmon color.. I first heard of this from Mac McClanahan in the early 1980’s and then I tested it. It seemed true. Further use of it in my work, and my students has made me more certain..  The year after testing it I was a resident at The Archie Bray and read about the water gas reaction being used to reduce iron oxide in brick and lowering the maturing temperature of pavering block in Archie’s old library. I became a believer.

The next fuel in the mix is CH4. Given enough oxygen this just burns to water and carbon dioxide, just like it would coming from a pipe.  The Hydrogen generally goes to water first but given some existing water some of it becomes hydrogen. This is the part of this that makes me squirm and wonder if the model is correct. Some of it if mixed with air poorly or if the oxygen mix is too low becomes soot and water.  This is part of the reason that firebox design  in wood kilns seems critical. Methane burning with suffient oxygen has a blue color.

Carbon monoxide, just as in gas kilns appears to be the main reduction agent lingering in part, if you are firing in reduction, until it comes out from the kiln. The yellow orange flame at the flue or spy holes, if not the result of sodium flare, appears to be the carbon monoxide burning. Oxy -Hydrogen flames have a similar color but are much weaker in light. This can keep things confused I think. I believe that this color is more towards red, but also has a small component of blue…

It can be really difficult to determine the source of a flame color. It is important in learning to do this to evaluate the hue as this changes by source. There are several different fuels with yellow orange flames.

In a kiln, you only see flame where there is enough combustion to create enough light. I suspect that the water-gas reaction also produces light…

This brings us to carbon, soot, C, is of all of these fuels the hardest to burn. The first part of this is that it just needs a higher temperature to combust. I believe that Cardew states that this is 650˚C and I have seen other reference to 660˚C..  Cold air can extinguish burning carbon.. It also produces less heat per gram. The third is that it tends to clump when it is produced and can only mix with air on its outside layer. It has the ability to lengthen flames if the kiln has sufficient oxygen. Carbon may have an important role in evening the temperature in long single chamber kilns….But soot leaving the kiln is wasted fuel.

I wonder if having multiple stoke ports along with its obvious use in evening temperature also contributes to a bigger distribution of salmon color as it puts the hydrogen closer to more of the ware….

Burning charcoal that has lost its volatiles requires hot air. Since it only burns on the surface it goes away slowly. Maintaining the heat is critical to burn charcoal and this is one of the important aspects of Bourry box kilns. The do this by putting the location to burn charcoal after the production of methane and hydrogen and after where these gases start to burn.






Archie Bray Foundation Front showing bottles by Louis and stack of Gail's

Archie Bray Foundation Front showing Louis’ soda fired bottles and stack of Gail Busch’s in the window. Brick were fired in the brickyard.

 

Air Bubbles

Unfinished.
There are a lot of oversimplifications. In some ways any statement can seem one. Sometimes oversimplifications contain truths but fail at conveying understanding.

“Air bubbles cause explosions” is an example of an oversimplification common in my field of clay work. Often this is explained as “just untrue”, “air bubbles do not cause explosions”. Unfortunately, to me these examples both are partial truths and partial falsehoods. It makes me uncomfortable to write them down. 

In order to understand how air bubbles encourage explosions you have understand what an explosion is, and when it takes place, why. I am going to leave out explosions in air, in many ways they are a separate case.
Clay explodes not because of steam. Steam is part of the picture in most clay explosions. The clay explodes when the wares ability to contain the pressure of the gas inside is exceeded. Strength is important. It is the most important reason why it is harder to explode bisque. Bisque is stronger and can contain, hold, withstand more pressure. Porcelain may be easier to explode because of less pore space, but it is also because it tends to be weaker as greenware. Paper clay may explode less because of pores letting the pressure dissipate, but also because the paper fiber vastly increases the tensile strength of the greenware.
If you think of a quarter inch slab of clay 4 inches square, you can also think of it as two 1/8 inch slabs connected where they touch. Each of these slabs is stronger because of the other. When you think of them disconnected they are less strong. The reason that air bubbles preferentially explode is because of the weakness in the wall that the air bubbles create.

Things that decrease pressure from steam

  • open pores from grog, course clay, pinholes, other inclusions.
  • slower heating
  • dryer clay

Things that increase strength

  • lack of air bubbles or other strength reducing imperfectionsor inclusions
  • fibers
  • stronger clays. Some ball clays are chosen in industry to increase dry strength.

Clay can also explode because of organic inclusions and water of hydration of clay and other minerals. Colemanite chunks in your clay can cause explosions. So can plaster. Likely there are other theoretical causes.
—
— additions in response to questions
-Evaporation in a closed vessel (or one with small holes) is a complicated dynamic. I will try and explain it all in a way that can easily be understood. I have not tried before.
-Standard pressure is the pressure of air at sea level. It varies some,,, but it is a good place for a standard.
-I am going to leave out discussions of partial pressures. They do not seem needed at this point. But really understanding this might require it. One step at a time.

As water evaporates or turns to steam it absorbs energy. The molecules in water become more energetic and “bounce around more” so they act as a gas rather than a liquid. This is a substantial amount of energy. So, it takes a while to increase the heat past boiling to evaporate much water. The temperature of a pot of water in air essentially does not raise above the boiling point until all the water is  gone.  This is why your pot of water on the stove does not all instantly evaporate when you get it boiling. You have to add more heat to it. To make things simple, it takes 70 calories to bring 1 gram of water from 30 degrees to 100 (One calorie per gram per degree C). But it then takes 540 calories, at room pressure to evaporate it. Until you add the extra heat it will remain a liquid. So this process is not instantaneous. In a kiln at that temperature you are mostly transfering heat to the ware via convection. It is a slow process. This is part of why you can have explosions when the kiln is at 250˚C. The water has not had the heat added to it yet in order to evaporate. Convection is slow unless the temperature difference between the ware and air is high.
At sea level water boils at 100˚C (212˚F). As you go down in pressure, as happens as you gain elevation, the boiling point goes down.
As you increase pressure the boiling point goes up. This is most of the reason pressure cookers cook faster. They cook at higher pressures and hence the water in them gets to higher temperatures. The pressure comes because the water has enough energy to become a gas but is constrained by the volume.
So as you make steam in your clay by heating above 100˚C the pressure increases. If it is small enough to not explode the work, this increased pressure slows the evaporation because you now need to climb in temperature as well as add the heat of evaporation. Hopefully the steam leaks out through the pores fast enough that the pressure does not get greater than the clay can hold.

I hope that this is clear enough to make sense.

In glazed near vitreous ware that has gotten water into nearly closed cells traditional drying below boiling is not very effective.
Consider a long very narrow tube connected to a small container of water where the tube is the only opening to the outside. Just for an example lets chose 95˚C . My numbers are approximate.
Lets also assume that the tube starts completely saturated with water vapor. This is about 80% steam.
There is no great force moving the steam out of the tube. The way it leaves is via diffusion into the atmospheric air. As the water is creeping out via diffusion the air is creeping in. In a long narrow tube this happens very slowly. Until the percentage of steam over the water drops, no more can evaporate.
Bringing the temperature to just under the temperature of boiling does not help this dynamic. It just raises the percentage of water in the gas in the tube closer to 100%
Two things do change as you raise the temperature. The viscosity drops and the surface tension drops. These two properties do change the dynamics of drying in clay. As they drop the water is more able to spread out on surfaces providing more opportunity to dry, and also to spread more evenly through an object. But with really small pores it likely does not help enough to make much of a difference. Very little water will close off the pore.
It is my opinion, I do not treat this as fact, and I am not responsible if you blindly accept the ideas of some retired clay dude and blow up refires, that the best way to dry out refires is to get them near boiling, hold them at that temp until they are uniformly hot and then slowly raise the temp past boiling. I use 113˚C as the top temp if things are very thick and have soaked in water. I have used 2˚C per hour,, I suspect it is excessive.
The problem is that thermocouples and meters are not particularly accurate, even type R pr S unless you calibrate them and spend big money. Consequently you need a buffer for error.
As you add heat above 100˚C (assuming sea level) you will boil some of the water. This will increase the pressure in the container and force water and steam out of the tube. So long as the container, your clay body can withstand the pressure (better not be to high) the water will be expelled. Just before I retired I used a slow rise rather than a hold at ~110˚C to finish drying stubborn items and take care of cold spots.
The last couple of years I have thought that a long dry below boiling was a waste and that trying to get just above boiling would be more productive. The problem here is that kilns are not even in temperature and as they get older and leakier they get less even.
—
This discussion parallels high temperature drying. Once your ware is leather, unless it really is close to not being able to hold itself up, drying at a high temperature is superior. The low surface tension and viscosity of water at higher temperatures allows the clay to remain more evenly wet. How slow it dries is based on how fast you bleed humdity out of the container holding it. This might not be particularly good for kilns, but I think that its problems are over-rated and the real problem with corrosion is from the organic acids from organic matter. Somewhere I have something written on this process.
[answers to questions and clarifications added]

Clayers Like it Hot!

Clayers like it hot. We just need the heat to be inside the correct box.
Ice Point
This short essay touches on a lot of things, I will try and get it in a good linear organization.
Thermocouples work because metals exposed to differing temperatures in different places develop a voltage between those two places. Different metals produce differing voltages. So when you take say a chromel wire and an alumel wire and connect on end at the other end you will have a voltage dependent on the temperature at each end. These voltages are not linear. So if the meter end is at 70˚F and the connected end is at 170˚F you get a slightly different voltage than if cold end is at 75˚F and the hot end at 175˚F.
Further, if your two connections at your meter (you meter is almost certainly made with copper alloy wire) are at different temperatures you get two more thermocouples at the meter throwing off the measurement. Thermocouple wire, chosen to match the properties of the thermocouple usually connect the thermocouple to the meter (unless the thermocouple is directly connected).
The standard temperature for the end by the meter is 32˚F(0˚C), known in this context as the “ice point”. In order to get accurate readings you might have once placed this connection, watertight, in a bath of icewater. For years meters had electrical compensation for this temperature to make the meter read as if it were at zero. This was refered to as “ice point compensation”. Newer quality meters read the ambient temperature with a thermistor and compensate digitally. Cheaper meters assumed that they were at a particular temperature say 75˚F.
Old analog meters with a needle dealt with the non-linear aspect of thermocouples by printing a scale that was also not linear. Some parts of the scale had lines drawn closer together than other parts of the scale. It was a clever, inexpensive way to deal with the non-linearity.

Because of compensation, kiln control boards likely have on-board temperature sensing. Once they have that it is trivial to design a board to turn the kiln off if the ambient temperature is too high. In the US, having the means to turn off a malfunctioning kiln or kiln operating at an unsafe temperature is a liability issue. It also can vastly reduce kiln lifespan.

Derating of Electronics
Most electronics is designed to operate at or near room temperature. Cars use specific components that are vibration and heat resistant. The military and NASA have their own set of requirements. As you raise the ambient temperature the amount of current a device can take at one time and its lifespan falls. Even if a device is rated at say 120˚F it may fail sooner if operated or stored that hot. It also might need a larger heat sink (piece of aluminum designed to dissapate the heat).
Every electronic and electrical component in the kiln has a temperature rating. Just like elements fired at a higher temperature, power cords, relays, outlets, and control boards are going to fail sooner if operated at a high temperature. Circuit breakers trip sooner in hot weather too. Further as things get hotter, corrosion speeds up.
***Entropy discussion fits here.

I do not know exactly at what temperature Skutt Control Boards give a high ambient temperature warning, but I expect that the boards themselves are already above 100˚F. Heat gets to the control board a lot of ways, but there is insulation blocking much of the radiated heat, openings for convection, and little washer like things between the red box and kiln shell. Still the red box does heat up and consequently so does the control board. You can place a small fan to blow through the control box, something like an old computer fan, not a box fan. You want to avoid fans blowing on the kiln case.
Things that can be done to limit the heat in a kiln room. Open it up, windows, doors, fans in doors. Fire at night (make sure that you do not sleep in a house with a firing kiln). Start early in the morning. Fire faster so that less heat gets out of the kiln before you are done. Fire so that the hot part of the firing is in the evening if the outside temp is greater than 100 during the day.
My insulated studio gets warm in the winter with 1000 watts of heat. Your kiln say drawing 40 amps at 240 volts is just under 10,000 watts. This is a lot of heat and your air conditioner might not want to keep up with it. Plan ahead.
Please do not hang out in very hot kiln rooms and drink enough water. But make sure, especially in hot environments that you monitor your kiln.

Controlling Glaze Application Thickness on Porous Bisqueware.

Controlling Glaze Application Thickness on Porous Bisqueware.

Factors controlling the thickness of a glazecoat on bisque.

  1. Length of time in the glaze
  2. Density of the glaze suspension. That is how much water is there and how much suspended powder.
  3. (Apparent) porosity of the bisque, including how dry it is, how much pore space it has, how quick the pore space absorbs water, and how thick the bisque is.
  4. Rheologic properites.
    • a. flocculation
    • b. surface tension and viscosity
    • c. number of long molecules (might be covered in viscosity)
    • d. The amount of fine particles that can clog surface pores.

Length of time in the glaze

When you dip a piece in your glaze suspension the bisque ware starts to absorb water first making the glaze near the surface a more dense liquid and then turning it solid. So long as the bisque is absorbing water fast enough the glaze coat continues to thicken. As the absorption slows down there reaches a point where the coat of stiff glaze starts to get wetter again and slough off. The thicker the work is, the thicker the glaze can get and the faster it gets thick. In beginning thrown work the base of the pot is often thicker than the top making the glaze thicker near the bottom, just where running has the biggest likelihood of causing an issue.
Dipping the work in water before glazing decreases the availability of pore space for absorbing glaze. Right after you dip it the effect is greater. Because water without glaze absorbs quickly these have to be very fast dips. With work that is thicker near the bottom you can dip the bottom few inches in water before you glaze and if needed pour a little water on the inside bottom and pour it out. I do this with really runny ash glazes so that they will not run too thick on the inside.

How long a pot is in the glaze is perhaps the primary method of control of glaze coat thickness. If you imagine pushing a cylinder in for 5 seconds and then removing it for five seconds, the first part of the pot to enter the glaze will be in the glaze for ten sends and the last for less than a second. If you want an even coat of glaze, you will not have it. I use the words plunge, wait, pull. Don’t go so fast that you create a tidal wave or splash but do not take your time putting the pot in, or taking it out. After you pull it out you usually want to keep it in the same orientation so that you do not get drips down the side of the pot.
If you are doing two different glazes, the amount of time you wait between glazes controls the thickness of the overlap. The longer you wait, the drier the first glaze becomes and the more porousity it has avaialble to dry the second coat of glaze. Being ready with the secoond glaze saves loads of problems. As soon as the high sheen is gone it is usually safe to dip in the second glaze.

Density

More solids in the glaze means that the pot has to absorb less water to make a stiff coat. This speeds up how quickly a coat accumulates. Adding water can work to a point but it also increases the shrinkage of the coat as it dries. With too much water sharp edges of the clay become saturated and get little or no glaze. There are many ways to test the thickness of a glaze coat and to control it. The first measure of control is the density. How much does a given volume weigh? Adjusting that by adding water (it decreases the density of the glaze) is the first thing to do after checking if it is too dense.
Glazes should be stirred immediately before glazing. Some glaze mixtures are particulary sensitive to this. Further, since materials settle out at different rates an unstirred glaze is a different glaze at the top than the bottom. There is a particular watery look to the last part of a pot dipped into an unstirred glaze.

Rheology

The rheology of the glaze is the next issue to deal with. As you speed the absorption of the water needed to stiffen the coat and as you reduce the water needed to be absorbed you cut down on the space between the particles of glaze. At least this is the theory of Matt Katz, and it makes sense to me. This decreases the amount of air that will be trapped in the melted glaze coat and cut down on pinholes. Adding a deflocculant helps with this as it reduces the amount of water needed to make glaze fluid. Shorter dipping time also helps. Matt also favors low bisques because it increases the force and speed of water absorption decreasing the pore space in the glaze coat.
On the other hand flocculants seem to cut down the amount of thickness variation created by drips flowing off handles or bottoms of pots when they are pulled from the glaze slurry. Since you cannot deflocculate and flocculate at the same time, you have to do what is needed more depending on the glaze.

Fine Particles

Fine particles, especially bentonite, also help to keep drips from setting in thick streams. The fine clays clog the surface pores as the pot is held in the glaze. So once the glaze reaches a certain thickness the rate at which it absorbs water slows down decreasing the impact of drips as you are applying glaze. It is a good reason to add bentonite to most any glaze. Veegum does this too. Glazes with lots of ball clay do not need the addition.
Other additives such as gums, glycols, can slow absorption even further. Some of these materials affect the rheology in multiple ways. They can be deflocculants, or flocculants, they can affect the surface tension or viscosity so test them. Make sure that your kiln is vented regardless and avoid things that you should not have your hands in or are hazardous to burn.

Ways to check glaze thickness

  • Scratch through the applied glaze with a pin tool and look at the thickness of the coat.
  • Look at the glaze coat and see how it covers details,rounds off rims,  and look the thickness at the edge of the coat. This is harder than it seems and takes practice.
  • Make a thickness gauge out of a dial indicator. I am hesitant to give directions as I have not used one.
  • Make a thickness gauge out of a piece of metal with a series of teeth that will scratch into the glaze coat. I believe that I read about this in Cardew’s “Pioneer Pottery” but it could be Leach’s A Potter’s Book”

 

In order to do this you need some vocabulary, a mental scale of thicknesses. Although if you are using a dial indicator a numeric scale might make sense.

  • Light Wash. A thickness where you see more clay than glaze. The wash is only thick in recesses if anywhere at all. Likely it does not show at all on sharp edges.
  • Heavy Wash. The coat mostly covers the clay but you can see some clay showing through on flat areas of bisque. Usually it is thin on sharp edges.
  • Just Opaque. A little heavier than heavy wash, you cannot see the clay on flat areas at all although edges may show.
  • Photo Paper Thickness
  • Half the thickness of a dime
  • The thickness of a dime
  • Penny
  • Nickel (US or Canadian coin)

Drying of Clay, thoughts, experience, ideas, dynamics, principles.

Understanding the problems of drying thick work.
It would be easy to assume that drying work that is twice as thick takes twice the time. There are many confounding variables in this, and the simple picture is just not true.

It takes only a little heat to heat water up. It takes 1 calorie of heat to heat 1 gram of water 1 degree celcius. Just to get some comparison, scale in this, a kilowatt hour is 860 thousand calories. Just to avoid confusion, a nutritional calorie is 1000 regular calories.

But to evaporate water, to turn it to steam takes 540 calories for each gram. It takes time, or a big heat differential to transfer all of that heat to the water. As the water evaporates it absorbs heat from its surroundings, cooling them. This is why we sweat to cool ourselves. Evaporation of water absorbs heat.

Clay, especially dry clay is a reasonably good insulator. If you think of that 2 inch thick dinosaur as a bit of water surrounded by insulation, an inch of clay on each side, it is going to take some time for enough heat to penetrate the clay to evaporate the water. Remember, just heating it to boiling is not enough to evaporate it, you have to also get 540 more calories per gram to the water.

Below the boiling point of water at normal air pressure you can only evaporate water until the air surrounding it is saturated, until the relative humidity surrounding the water is 100%. So if you heat clay to say 90˚C or 194˚F and the clay is thick, water inside the clay will only evaporate until the air in the pores is saturated with water vapor. It may not all evaporate until there is time for the water vapor to move through the pores and be exchanged with air from outside the clay.

Explosions happen because the pressure inside the clay exceeds the strength of the clay to contain it. This part of the dynamic creates some compounding factors. As the pressure increases, so does the boiling point of water. This property likely contributes to the wide range of temperatures that we see explosions taking place at. Insulating properties of clay also contribute. the outside of a pot may be above normal boiling, but the inside might be colder from insulation and be at a higher pressure.

Fortunately, not everything makes getting clay dry more difficult. There are a few factors that speed things up. The first is that water wicks through the clay and presents itself, at least in part, at the surface of the clay where heat exchange and drying is easy. In order to understand this well you need to understand three terms, capilarity, surface tension, and viscosity.

Viscosity is the rate at which a liquid will flow. Honey and molasses are much more viscous than water. Acetone has a viscosity that is less than water, but most common liquids have viscosities that are higher. Viscosity of water decreases substantively as temperature increases. This increases its ability to move through clay towards the surface as temperature increases.

Surface tension is a nice term. It describes the tension on the surface of a liquid. When water beads up on a waxed surface the beading is because of surface tension. Without surface tension it would spread out. Surface tension is what holds bubbles intact. In mold making and in bubbly glazes a light spritz of alcohol can cause bubbles to burst. This is because even small amounts of alcohol radically lower the surface tension of the water allowing it to spread out and the bubbles to burst. Surface tension of water also decreases quickly with the rise in temperature. This allows the water to spread across surfaces, say clay particles and present more surface area for drying.

Capilarity, the property of water to up thin tubes or pores decreases slightly with increases in temperatures. The decrease is small enough that in most engineering problems the decrease can be ignored. Due to the increase in speed that this happens due to the decrease in viscosity, in our case it is more ignorable.

The loss of viscosity and surface tension presents us with an opportunity. Clay held at a high temperature maintains a more even wetness because water more easily transfers itself from wet to dry areas. Clay, in general, can be dried more quickly with few problems at high temperatures than at low. The phrase “high heat high humidty drying is used in an old text on brickmaking in the Archie Bray Foundation library and is the place I first encountered the concept. A few years later I needed to dry a thick carved mural quickly and dried most of it at 180˚F in a kiln with the lid propped over night, and some on a table with a fan. The ones on the table all cracked, those in the kiln all did not crack. I was convinced.

In this there are other confounding factors. Almost all electric kilns with the doors open tend to have colder floors. Even with zone control, unless there are floor elements this is likely to be the case. This is because cold air is denser than hot air so it settles pushing the lighter hot air out of the way. The more a kiln leaks, the more trouble there is with cold floors. Drying with the door open is an extreme case of a “leak”.

How wet work is changes the amount of time needed to dry below boiling temps significantly. It conspires with thickness to make thick objects often seem impossible to fire successfully. We have all heard the untruth, “You cannot fire thick work”. Having successfully fired kiln pugs as counterweights, I know this to be an untruth.

While I am still a believer that convection leaves bottoms of kilns colder than tops much of the problem with cold kiln bottoms seems to be the shelf near an uninsulated floor adding to the thermal mass . Work loaded on the shelf with the bottom down adds even more to this. It is not a duplicate of the area near the lid of the kiln. Dispersal of heat at low temperature has to be from convection because radiation is not very effective at the low temperatures.   Since none of these factors are very effective with low temperatures or small differences in temperature the added density at the bottom keeps things wet longer. Keeping thick work off the bottom and when possible placing it rim down vastly improves the situation by getting more of the clay higher in the kiln.

Most dispersal of heat at low temperatures in kilns is from convection caused by the differences in density caused by air temperature. The colder air heats at the elements near the bottom. This often leaves a cone of colder area near the bottom of electric kilns. So when you are preheating at 180˚F the bottom of the kiln, especially towards the center can be several tens of degrees colder. The colder it is, the less heat is transferred to the water and the slower it evaporates. Most often it seems that explosions happen in the bottoms of kilns that are fired with some, but not enough care.



Optimal conditions are unachievable. We have to fire in real situations. But if you had a piece of clay that was slightly wet, you could heat it above boiling for a short time. The water near the surface would evaporate quickly, but being near the surface would not create any pressure within the clay. The evaporation would prevent the water further inside the clay from heating as it would be absorbing so much heat to evaporate. After that surface water evaporated you would need to lower the temperature. The question is what temperature to lower it to? Optimally this might be above boiling. We only need to stay beneath the pressure that the clay can withstand. Under perfect circumstances we could even do this with leather hard clay. I believe that under normal circumstances we almost never achieve perfect drying and some water is always expelled from the walls of our clay under pressure.

Kiln pyrometers, even type S are imperfect. Even a few degrees around boiling could likely create problems with explosions. Because of this I usually used large margins. I started at 180˚F (82˚C) moved to 190˚F and as I got surer to 200˚F (93˚C). As I got close to retirement I started to use a slow rise time through boiling and shorten the hold. I believe that fine tuning this would result in quicker firings. Because there are differences in our many clay bodies and firings are mixed, “optimal” will vary even beyond considering thickness.

Sometime when I first started teaching at Texas A&M University Corpus Christi, The Island University, The only university in the US on its own island, surrounded by salt water, I decided that I needed a goal for speed of bisque kilns. How many pieces was it acceptable to explode in a semester? If you fire too slow you waste student time, and some electricity. If you fire too fast you either have not allow thick work or you blow stuff up. I decided that blowing up two pieces a semester was enough. Five was way too many. I also decided that this was true regardless of thickness. I started holding back thick work for special firings.

I dried kilns at 195˚F roughly 90˚C. How long the kiln was held depended on the wetness of the work, and how thick it was. I avoided loading thick work near the floor of the kiln. As things got busier and there were more classes, kilns were loaded less reliably. Work on the bottom started to explode more. I added time, a slow rise and then a short hold at 20˚F above boiling to try and get the bottom of the kiln to not explode. This was effective.

I started to think about the slow rise and the ability of clay to contain some pressure. I think that the optimal technique for getting work dry might be a short hold below boiling to get the work hot throughout and then a slow rise past boiling keeping the rise slow enough that the water remaining can boil without creating too much pressure. I think that this would be worthy of study. Knowlege of optimization of brick drying could likely inform what we do and save us time, money, and carbon.

Glass ลุงแก้ว

Written prior to Uncle Glass’s death in 2026. He will be missed by all who knew him.

พอเพียง Paw Pieng translates as “enough”, or “sufficient”. It is one of the mottos and goals for the Thai People put forward by Rama IX, HRH King Bhumipol The Great. When he came to power there was a great deal of poverty and he wanted development projects that would provide enough for the people. His plan calls for reasonableness (or wisdom), moderation, and prudence. He said that the underlying conditions for this must be knowledge and moderation. Over the years before and during his reign its often been clear that there must be an economy of self sufficiency, that the country should be able to live without the outside world, be able to shield itself from the valleys of the world economy. In my mind I have decided that the word “sufficiency” is a better translation of this idea than “self sufficiency” because it stresses “enough”. Learning a little about this philosphy gave a new context for an old friend of mine, one of my personal heros, ลุงแก้ว Uncle Glass .

Uncle Glass is a very funny, joyous man. He is fast to smile, crack a joke, pull your leg, and smile again. He is not “well educated” but is very smart, and it would be mistake to underestimate him. He has a bad leg. I do not remember how his leg was hurt, his calf broken, but it was when he was a young man, maybe in his teens. He was put into a cart and taken to the doctors. The doctor said that his leg below the break would need to be amputated. The monks from the local Buddhist temple said that they could heal the leg. They took care of him, bathed him, changed his clothes, and fed him. I was told how long this healing took, but I remember only that it was most of a year. Lung Gaeow (Uncle Glass) can walk, but for most of his life he found a bicycle a better mode of travel at least for distances more than about 20 meters.

Until he retired, Uncle Glass lived in what in the US we might call “a shack”. It had a tin roof over the old one made of leaves or grass and short posts, and a wood floor. The walls did not protect from the wind much. His first wife got ill and he cared for her until she died. He remarried someone that he knew from school. I think he was in his fifties when this took place. She developed diabetes and became bed ridden. He cared for her until she died. His third wife he married only so that the village would not talk. She was already in bad shape and he could not care for her without there being gossip unless they were married. She was still alive in 2008 if my memory is correct. The world could use more people like him. He is a mensch, a great human.

When I visited him back then (2014) he was going to the river every morning on his bicycle, maybe about a 1 km ride. He would park and climb down the banks. At the river he set some hooks with bait and then wash. He carried water up the bank (maybe 20 feet down) and watered his garden. After several loads he would pull out the fishing gear. When I was there he caught about 5 skinny 4 inch fish. Up on the bank he put them directly on some leaves he set on fire. Then he sat down, got out some glutinous rice and spicy vegetables, and a shot or two of whiskey his son in law packed for him. The fish, now cooked dry, were packed in paper and he rode is his bike off to the pottery to make water jars. A good person helps people in need. A great person does this again and again. I had hoped to make a video about him, but I started just as his physical productivity was failing from age.  As I write this he is still a joy to be around.

Lung Gaeow appears in my Thai Pottery Video in the height contest( https://www.youtube.com/watch?v=zi_t0y5jFxM&t=409s 02:57 ). After I returned to the US I was asked to write for grants to bring Thai potters to The National Council on Education for the Ceramic Arts Conference in 1991 in Tempe Arizona. Suwanee was to deal with all the arrangements in Thailand. I first asked for Uncle Good. I thought that he was nice, and had a love for making pots. He had a nice way with the traditional forms. He decided that he could not come because he was afraid that we would not have rice in the US and he could not eat bread. The word “eat” in Thai is really “eat rice”. The bread they sold in his part of Thailand was used as a desert dish, sort of like ultra-sweet Wonder®-type bread. The second person on our list had no birth certificate so they could not get a passport. Suwanee asked around. Finally two men agreed to come, “Craftsman Shotglass” (Chang Jork), and “Uncle Glass” (Lung Gaeow).

Lung Gaeow and Chang Jork (now deceseased) had a problem with alcohol. They were not anyone’s first choice but they were brave enough to come. Had I known more Glass would have been first on the list. My sole job at the conference was to take care of the 5 Thais, Suwanee (who could take care of herself) her sister (who stuck close to Suwanee), Mae (mom), and Chang Jork and Lung Gaeow. My Thai was rotten back then, but things worked out. So the morning after they arrived I went to see them. Gaeow says, “Louis, great to see you!” We are talking,,, how was the flight etc. “Louis, the flight was very nice but the airplane was cold, they brought us blankets.” “And you know Louis, they do have alcohol on the plane, I was worried. But it is so expensive and bottles are so little. Is it that expensive everywhere in America?”. I said, “no” .”You know Louis, we have alcoholism. Could you take us to buy some?”

So, I took them to the local alcohol store about a mile from their apartment. They walked in behind me. Gaeow grabs my arm kind of hard, it hurt a bit, “Louis, (he swings his arm to point across the store) Is all of this alcohol?” I answered, “No, that case over there is soda and Coke”. He said, “Louis, America is a great country!”.

He said, “Which type should be buy?” We finally settled on cheap beer. I picked up a six pack. They picked up two each. I showed them how to pay for it and we took it back to the apartment.

A couple of days later I stopped at the apartment. “Louis, we need more beer.” So we went back and got more. Gaeow told me that Jork could not read. Jork said,”Gaeow can’t read”, show us how to do this, then we won’t have to bother you.”
A few days went by. I was looking for them. They were not at the studio, not at Kurt Weiser’s house and not at the apartment. Then it dawned on me, “They are at the liquor store”. So I drove over to get them.

I walked in and they were not there. I turned to ask the cashier. He recognized me, “Its you!Where are those to guy’s from?” “Thailand”. “What language do they speak?” I answered “Thai” although really talking with each other its the local dialect. The cashier asked, ” Do you know what they did?” I am half already amused and a bit fearful.
“The rolled a big cigar with newspaper and a bunch of tobacco I think. The do smoke tobacco right?” I nod. ” You know, you can’t smoke in here” . I said that I would tell them. “After they lit that cigar, they squated in the back of the store in that language, What language did you say that was?” “Thai”. “Yeah, thats it. After a few minutes they came up to the counter, put thier hands on it and said, “Alcoholism, Alcoholism”. “I sold them some cheap whiskey. “You might want to tell them that they can’t drink in the store”. I thanked the cashier. As I was leaving he said, ” tell them the should not drink on the street either”.

So I head back to the apartment. “Louis!” Gaeow says,” I guess you were looking for us” . I said, “yes”. “Did you go to the liquor store?”Gaeow looks at Jork. “Yes” I said.
“I guess that the clerk said to tell us not to smoke in the store” I said, “Yes, it might explode”. “And we’re not supposed to drink in the store either?” “yes”. “Why not?” . “They don’t want drunk people in the liquor store”. Gaeow says something like, “how do they expect to make any money”. I tell them not to drink on the street. “They ask, “If we do, how much do we pay the police?” I explain that it is probably a mistake to try and buy off the police.

Chang Jork stopped by at Umdang Pottery when I was there in the early 2000’s. He gave me his Saw Duang ซอด้วง. This gift was probably the most significant of my life. He was not long on possessions. This was a return gift for bringing him to the US. He died a few years later.

I tried to see Lung Gaeow nearly every time I went to Thailand. He is my elder. If I was to visit him I needed to bring a gift. Normally this would be fruit, but he is an alcoholic so whiskey is what is expected. I no longer bring a full bottle.
Anyhow, I went to visit him about 15 years after his trip and he said, “Louis, Thanks for the whiskey. The neighbors don’t believe I ever was in America. Do you have any pictures of me there? And can you bring them here tomorrow?

I did not really understand this request until I stopped for another bottle of whiskey on the way the next day.

I saw Lung Kaeow last in January 2026. He was nearly completely blind. He was still smiling and laughing. I recently learned that some called in “Kaeow America”. He died April 18, 2026 . There are a few great people whose being seems to stick really hard to mine. He is one. He was one of the poorest great people I have met and also one of the funniest people I have met. His life enriched those around him with laughter and humanity. He will be missed by all who knew him.