Author Archives: Louis Katz

Air Bubbles

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]

Where is the Functionality in Students Learning Calculus in High School When Few People Use Calculus in Real Life?

-a tribute to Mr. Alvin Mayes who taught Calculus to me 50 years ago, and an unnamed graduate student who taught Calculus at the University of Michigan a year later-

Some of this will not be understandable by those that do not understand calculus. None of it will be understood by those who do not try.

Calculus is a language and way of thinking, a way to describe properties of the real world and to learn about them. It was first discovered by Newton and not published and then discovered by Leibniz. Although it is used for other things it provides a language for describing the properties of curves, an advanced vocabulary for some properties of solids, and ways to understand the cumulative action of forces on the movements.of objects. It has its little fingers in every aspect of our life.

I cannot say that I use calculus as much as I could or even should, but it does get used when I press the accelerator of my car. I think about it as I turn the water down as I am filling a container so that it won’t overflow. Acceleration, and deceleration are topics covered in calculus classes. When you leave a stop sign do you depress the gas pedal at a constant rate? I don’t. I press my foot down rather quickly at first because I want people to know quickly that I am moving and then slow the depression of my foot with the rate moving towards a steady state when I am at speed. I am sure that how I do this is not optimal for gas savings. How I do this is a compromise between safety, speed of travel and gas. I also try not to tax my brain too much as I drive. My understanding of this is informed by my understanding of the curves that describe the motion and its affects.

I have taught a lot of pot making over the years. It might not be the most effective way to teach about form, but for some people the discussion of form is best done classically by breaking it up into pieces that can be described. There is more than one way to cut a cake, and really you do not always even need a knife. But one of the ways I do this is to talk about how the radii that are tangent to the pots curve at different places change in length. I should be clear for the mathematically inclined that I do not discuss slope as described by my Geometry teacher Mr. Waldman as “der rise über der run” because it is not as useful as talking about a more linear seeming property, the rate of change of the angle of the slope. (By this definition a vertical line has a slope of infinity, a horizontal line 0 and a 45˚ angle one. The difference between horizontal and 45˚ with this concept is 1 and from thereto vertical is ∞ -1. This is not intuitive.) I talk about change of angle. With this a tight curve in any orientation has the same description. The radius of a curve at any point in the curve is a basic concept that I use in most other concepts about curves.

Studying calculus you look at a lot of curves, think of them in terms of rates of change, or acceleration, deceleration. When you push down the gas pedal at a constant speed your car accelerates, but there are competing properties at work. It is easiest to talk about in a manual transmission once the car is moving. At the low end, when the pedal is only depressed a little bit your car accelerates but as the pedal moves down further, if it does it fast enough you car starts to accelerate faster and faster. At some point near the “pedal to the metal” point, fully depressed, your car may still accelerate, but does so slower and slower. I have slightly redefined some concepts in calculus so that I can use them in life without having to work too hard.

If you are trying to get your car to say 60 kilometers per hour and do so quickly, you may push the pedal down rather quickly and find that you have to ease off when the car reaches sixty. At some point driving like this your foot stops going down and starts easing off. This is an inflection in the depression of your foot. Knowing where you should do this makes your driving smoother and probably reduces gas consumption. I suspect that not having an inflection at all probably saves more. Knowing where to depress your foot to to achieve a steady state and easing up on how fast your depress the pedal as you approach it also likely improves mileage. It also keeps your passengers happy.

An adult I used to drive with complained that the dog only threw up in the car when they were driving. This is because they used the accelerator similar to an on and off switch with no idea that a steady state might be better. That they used to teach calculus did not help them understand its application in driving. So it goes.

As a curve gets tighter its angular rate of change accelerates, it changes more and more quickly. As it gets broader this decelerates, changes slower and slower. When a curve goes from being concave to convex the mathematical description is that its second derivative goes from being a positive number to a negative one. The mathematical concept may not of much use to the casual user of calculus concepts. But the point of change between the concave and convex is a critical point in the description of some “complex curves” (my phrase, meaning a piece of a curve with a discontinuity in the first or second derivative or a curve that goes from concave to convex ) . This point, again where the curve goes from concave to convex is called an “inflection point”. Knowing precisely where this is in change from the belly to the neck in some jars or jugs makes recreating the object much easier.

A “first order discontinuity” (an abrupt change in the first derivative) is a place where two curves join producing a sharp angle. A “second order discontinuity” (second derivative) is a place where the radius of a curve abruptly changes. So if you take a 3 inch diameter arch and attach it directly to a 5 inch diameter arc so that there is no corner , this is a second order discontinuity. If one is concave facing up and the other is convex facing up,,,, going from concave to convex,,,,, then this is also an inflection point. A first order and inflection together is really quite unusual but does happen at the intersection of bellies of bottles to the shoulder. it can have a very different look and feel than the second order kind, you have to keep this straight. While I think about third order changes, I do not think that I can perceive them in products. I let them be as just abstract thoughts.

In throwing on the wheel the axis of rotation is always vertical. But a dear departed teacher Victor Babu, used to talk about taking a curve and slightly tipping this axis. He did not use the phrase axis of rotation. His way of describing this was in some ways better. He tipped the curve to be rotated. Not having a good phrase to hold the concept made this sometimes difficult to describe to some people.

In high school I did very little homework. This is in part because I hated writing anything. ADHD likely played into it. The “write it over stuff but make it neater earlier in my education made homework as a topic very unpleasant.” The only time I can remember completing homework regularly was when studying with a friend. I did learn. In 11th grade I was in the semifinals for the Michigan Math Prize competition. I think that this changed my standing in the eyes of Math teachers, but they already knew I was smart. I had not studied enough to have a chance at the finals. My high school owned this competition back then. It was a great place to go to school.

Because of not always getting all the concepts and not doing homework, not practicing, and errors in basic processing of numbers I got mostly B’s and C’s in math. I did get a D in 10th grade (might have been 9th grade) and my mother made me take a course over the summer. To the best of my knowledge I was the only person ever to pass Mr. Waldman’s Geometry class without doing my homework. I read the textbook over the summer before it. At the end of the first few days I took the first test and got 100 percent, then took another quiz . A few days later I took the final. Despite his policy of failing the course if you did not do homework, I got an ‘A’. Its fortunate, because if required to do homework I would have failed. Unaccommodated dysgraphia can be a disaster.

After my first class in Calculus with Mr. Mayes, a class I believe I got a ‘B’ in, I got a ‘3’ on an advanced placement test. This was not a high enough grade to earn credit for Calculus at The University of Michigan Engineering School. It did show that I knew much of the content. I had not memorized formula and rules for doing some problems. The class despite being difficult. I can remember the good nature of Mr. Mayes. He had an incredible smile an patience. But the ‘3’ meant that I had to take calculus in college. The TA was a joy. Starting at the beginning again it all quickly came into focus. I did not do the homework, but easily aced the class.

Notes on printing circuit boards in bulk, single sided,asphaltum, screen printing

Problems in Silk Screening.

  1. Kissing. This would be easier on a vacuum table.
  2. There were multiple places where the screen got clogged. This might have been from hard spots in the asphaltum.


  1. Etchant was intended to be mixed at 45 grams etchant to 100 grams water. For the 30 205x305mm boards I mixed 1.5 pounds of etchant to 1500 ml of water.  This was 47.6 % roughly oops.
  2. The intial etch was 20 (10+10) minutes. It seemed over done with some areas under the edges etched away. However, this was also the thinnest print so it is hard to know.
  3. The etching was done on my agitator,, a rocker. The container was rotated 180˚ after half the etch because the action of the agitator is not even. Centers etched slower. The fact that the ends of the board finished soonest points to the idea that the first board was not printed thick enough rather than being over etched.
  4. When successful etching times increased to 30 minutes I added about 250ml of concentrated muriatic acid to the bath. This would bring the etching time down to 24 minutes. I did this three times.
  5. Each morning a few tablespoons of alcohol were added to decrease the amount of etching that was clinging to the asphaltum after the boards were removed to keep from wasting etchant. It seemed to work well.
  6. After the first few I started prepping board by lightly brushing etchant onto the slowest parts of the board keeping two boards going through this process as one was being etched.
  7. Another board etching failure seems to have resulted from brushing the center of the board. The margins of the asphaltum were eaten under.
  8. several boards had areas where either the  printing was incomplete or damaged. These were repaired before etching with Zim Opaque Pen. This came off in the etchant about half way through. 
  9. final etching time was about 40 minutes. I decided to let the etchant wear out further so that there would be less to neutralize to recover the iron and copper.


  1. A mixture of about 4 -8 parts  Klean Strip 1-Gallon Odorless Mineral Spirit Substitute   was mixed with vegetable oil. This mix was much better for the initial strip than the mineral spirits substitute by itself. It appears that Klean Strip has either removed the word Substitute from the name or stores have stopped selling this product.
  2. I also tried some water based paint remover. It was not very good by itself but was functional as a secondary cleaner. It was less than optimal there too. It did seem to leave the copper without much oxidation. But given that I intended to soft scrub the copper before plating this was of little import.
  3. A secondary wipe down with the mineral spirit substitute worked better than other things I tried.
  4. Most of the boards were cleaned by pouring a Teaspoon onto the board and spreading it around. Then using a saturated rag often quite full of asphaltum, and light scrubbing. After that a wipe down with a cleaner rag and then used paper towel, then newish paper towel.



noodles เส้นก๋วยเตี๋ยว

Types of Thai Noodles เส้นก๋วยเตี๋ยว (if there is something wrong here, let me know at my firstname@domain
I needed to straighten noodle types in my head. Many of the words seem descended from Chinese and are hard to remember or pronounce.

  • Gao Lao เกาเหลา is a noodle soup usually served with no noodles.
  • Sen Lek เส้นเล็ก, with translates as little string shaped stuff
  • Sen Yai เส้นใหญ่, see Sen Lek, but big
  • Sen mii เส้นหมี่, this appears to be a rice noodle that is thin
  • Guay Jab ก๋วยจั๊บ These are sheets of rice noodle.
  • Khanom Jeen ขนมจีน . These are noodles made locally with a device that looks like a potato ricer. The rice flour is soaked for 3 days or so before being turned into noodles.
  • Ba Mii บะหมี่, wheat with egg noogles
  • Ba Mii  บะหมี่โคราช, Korat style ba mii noodles. I have no idea what makes them different.
  • Giam Ee เกี้ยมอี๋ These are a thick short rice noodle with pointy ends. The Chinese names are quite colorful . I do not think that I have had them.
  • Woon Sen วุ้นเส้น are made with mung bean flour
  • Ma ma มาม่า , บะหมี่มาม่า or ramen is a brand name of ramen noodle but it is a word used generically for ramen.
  • Gouitiow ก๋วยเตี๋ยว This seems to be a type of soup rather than a type of noodle. I find it tremendously hard to remember how to pronounce.
  • Khao Soi, is a dish that is different in different places. But in Northern Thailand it usually has fried rice noodles. But the name is for the dish, not the noodle.

Ethnocentrism and Flux

This seems an essay rambling through topics. Structurally it is all about the models we view the world with, their limitations and the power of stepping to the side and gaining perspective. In this the word “flux” refers to a group of ingredients and related concepts in glaze and clay.

Probably the single most important lesson I had in school was one on the word and concept “ethnocentrism”. I believe that the class was in fourth grade. It could have been fifth. I grew up in a suburb of Detroit, a “shtetl”, an area where greater than 90% of the people had Jewish ancestry. I believe that the word was part of the curriculum for that grade as others I have talked to had similar lessons. Its inclusion, not having anyone to ask about it, seems likely the result of, a response to, antisemitism, The Holocaust,,, ongoing problems. Cities near us did not allow Jewish residents, pools were segregated. For me the lesson on ethnocentrism was critical.

Ethnocentrism is the concept that from within a cultural viewpoint the actions of that culture seem consistent, meaningful, sensible and from outside the culture they can seem otherwise, bizarre, random, nuts, etc. The concept states that our feelings of our culture and that of others are framed, guided, by our cultural standpoint. Ethnocentrism has its strongest expressions in monolythic cultures, but certainly exists in multicultural environments. It is often, maybe always, a root cause of “isms” such as racism, ageism,  nationalism, religiocentrism, etcetera-ism. 
The lesson  and the thoughts related to it tied itself over the years to many different topics in my daily goings on. So many that it now seems like it is part of every day, every thought, every moment,, connected, a sinew atttaching my hair to my toenails, my thoughts to my emotions.

At the University of Michigan in a course in The Pilot Program, a living/learning environment/dorm/community at Alice Lloyd Hall I took a class called “An Overview of Low Energy Technology” taught by a multi-talented individual, Jim Burgel. One of the requirements, seemingly unrelated to this course, was reading, “Zen and the Art of Motorcycle Maintenance”. This book, although seemingly on a different topic than ethnocentrism melded into this topic. In some ways the book is about how our concept of the world changes how we perceive it, and how there are different ways to conceptualize the world. The differing rationalities described in this book seem consistent from the inside.

At the same time I was taking an Art History Survey course, “An Overview of Far Eastern Art” History taught by the late great Professor Walter Spinks. In it, at the beginning of each section, he tried to give us an overview of how a people perceived the world, what concepts guided their thoughts. I remember much of what he said about Taoism. I found it captivating. Later in the semester we discussed Buddhism and Zen Buddhism, and the illusory nature of perception and confusion of it with reality. Over the years it took hold. An interesting look at this is contained in The Jews in the Lotus, by Rodger Kamenetz. The book is a discussion of the events leading  up to a meeting between a group of Jews and the Dali Lama. The Dali Lama was trying to understand how a people can live and thrive in exile and wanted to talk with experts.

But in the book there is a short discussion of JewBu’s, Jews who become Buddhists. There seems to be a lot of these. It seems, although hard to quantify, that the Jewish mindset meshes well with Buddhism. I do not have any great insight on this. I cannot step far enough out of my own box to gain perspective. The one idea that I do have is that both frameworks are very abstract.

So, what does this have to do with “Flux”?
The word has many meanings, lots of definitions, and exists in many realms. But this discussion is its use in Ceramics. There are lots of definitions, complications,  overlaps, inconsistencies in how ceramics melt and sinter. The word and concepts are not simple subjects.

Perhaps the most general definition is, “A flux is a chemical that promotes melting”.  Great! It is a nice concept. It apparently is descriptive. It has nice defined edges. Something that does not promote melting is not a flux. 

As you add say calcium oxide to a clay body or a glaze that has none it melts easier and easier at a lower and lower temperature. The problems are that there is a lower limit below which it does not seem to help the melt, or at least not much. There is also a limit of the material above which it does exactly the opposite, prevent melting.
The relationship, and the problem with the word “flux” as it is used here is best illustrated with calcium oxide (calcia), aluminum oxide (alumina) and silicon dioxide (silica). These three ingredients form a nice looking stoneware glaze and sit close to some traditional celadon recipes from China. If you take the lowest melting composition, you can mix a recipe close to it it with one part of kaolin clay, one part ground quartz sand, and one part limestone. It simply demonstrates  the complexity. The limestone is traditionally called the “flux”. But if you remove or just lower the alumina the melting temperature goes up. Alumina in this composition helps the melting. It is by this definition a “flux”. The same thing is true of silica. As you remove the silica, the melting temperature goes up. It fluxes the alumina and limestone. It helps them melt. As you remove the limestone, the same thing happens. Each of these materials fluxes each other. Understanding this is critical to understanding glazes.
So the next most useful way to pidgeon-hole materials is to remove the silca and call it a glass former and alumina as a stabilizer or amphoteric. This makes the definition of a flux something that helps the alumina and silica to melt or sinter. This makes a lot of sense. It is unusual for us to add silica to lower and melting point. Normally what we seem to recognize and encounter is that adding it to glaze, after a certain point, raises the melting temperature. Alumina starts raising the melting temperature in much smaller quantities. But at temperatures down to the very low temperatures for glazes, little bits of alumina lower the melting points.
Hermann Seger developed the modern pyrometric cone,  a device for measuring the temperature and time components of the melting of glazes. Little tall cones of glaze materials, “cones” are made of the materials used for making glazes. At certain temperatures, after a certain amount of time they begin to melt and slump over. The can be spyed, throught what in the US is called a spy or peephole to determine the maturation of glazes in a kiln.
In doing so, he developed or at least further developed a system for analysis of glaze, still used today, called the “Unity Formula”. Rather than opperate on weights of materials, the unity formula uses counts of molecules, or moleclar equivalents in the glaze.
The unity formula is divided into three columns. The first is “The Fluxes” the second is “The Glass Formers”, the third is the “Modifiers” or amphoterics. But as simple as this seems, it too is an oversimplification, and some call the first column RO/R2O meaning items that take the form of an atom or two of a metal (R)  and a single atom of “O”, oxygen. The second column is the RO2 (one metal two oxygens) and the third is R2O3. Fine.
The material whose fit is seems the worst is Boric Acid, B2O3. By formula it should exist in the modifiers. But we add it to lower the temperature of melting, a flux, but it forms glass by itself and is a glassformer.  Most of us have left it in the third column but it needs to be thought about on its own.
We used to have a fourth grouping, “colorants”. Some of us still use this grouping. These are things that we add to glazes to change hues, or to add hues. The problem is that most of these materials also  act as fluxes, or help lower the melting temperature of the silica glass. Some of these exist in different forms depending on the temperature and composition of the gases they are melted in.  Some can loose oxygen as they are heated, some loose some of their oxygen if heated in a gas containing carbon monoxide or hydrogen, and some change how they function depending on their quantities, really all of them do. In terms of how they affect melting most of them belong in the fluxes. Some don’t and are glass formers.

I think that flux,glass former, amphoteric, is fine to a point. But thinking of things as melting is a limitation. Sure, they melt. But once we have a liquid using the vocabulary and concepts of solutions is much more informative. A solution of alumina silica and calcia above its melting point has an infinite ability to dissolve feldspar. Its ability to dissolve baria is limited, as is its ability to dissolve chrome oxide. At some point the solution gets saturated. Generally speaking in a saturated solution once the temperature starts to drop, things can crystalize out of solution if the mix does not become super saturated. This concept, solution, contains the complexity that happens as you add calcia to a  melted glaze.

Like many other things involving the definitions of words, “what is a flux” can become a turf war, especially between people who see the word or words as a real map of reality. For those, the word gets confused with the hopelessly complex reality. I too can get caught in this trap. I am not sure who does not or cannot. If the Buddha, the “all knowing and aware one” exists, than I suppose, again by definition, they are not confused. My belief is that the only real model for how the universe works would be another universe. I find more resonance in knowing how things flow, the patterns they make. This relates more to Taoism.

Words, the concept of them create a box from which we see the world. We define colors, speeds as fast or slow, temperatures as hot or cold, objects are cars or boxes, we create our world with our words and concepts.
Because of this I have a tendency to “dedefine words”. Art rather than being on object made by an artist, becomes “any object of intelligence”. But even this is not as broad as my real desire, nature too is art. So every object, idea, concept is art. Art is everything. It just become another “everything word”. It describes a particular set of glasses through which you view existence. The other problem in the “object made by an artist’ is that I define everyone as an “artist”. Everyone is expressive, everything the do is expression, and creative. 

Now there are ideas in the West that embody at least part of this connected all/everything. I call these ideas, or box them in, with the concept “everything words”. We here these all the time. “Everything is G-d”, Everything is Love, Everything is Chemistry, Everything is Physic, Math, Science, Psychology. And inside my box, I see everything as Art. The truth here seems to be that everything is everything.  But I find that I need to qualify this, Everything is Everything except when it is not.

คืนรัง คาราวาน หงา Nest, Night, sung by Nga (Sesame Seed) Caravan, also ขอมอบ ดอกไม้ ในสวน

With help from google, an old Caravan song I can now understand more completely. I have been listening to it for nearly 40 years and understanding more and more. Its time to put some work into it.
ด้วยความช่วยเหลือจาก google เพลงคาราวานเก่า ๆ ตอนนี้Louisสามารถเข้าใจได้อย่างสมบูรณ์มากขึ้น

คืนรัง คาราวาน หงา

โอ้ยอดรัก ฉันกลับมา
my dear I’m back
จากขอบฟ้า ที่ไกลแสนไกล
from the edge of the sky, the horizon, far far away
จากโคนรุ้ง ที่เนินไศล
from the bottom of the rainbow at the base of the hill
จากใบไม้ หลากสีสัน
from various colored leaves
ฉันเหนื่อย ฉันเพลีย ฉันหวัง
worn, tire, I hope
ฝากชีวิต ให้เธอเก็บไว้
to give her life to keep
ฝากดวงใจ ให้นอนแนบรัง
leave your heart to keep, sleep in place of comfort?(nest)
ฝากดวงตา และความมุ่งหวัง
leave your eyes and hopefulness
อย่าชิงชัง ฉันเลยยอดรัก
do not abhor me, I am so in love.
นานมาแล้ว เราจากกัน
long ago we parted
โอ้คืนวัน นั้นแสนหน่วงหนัก
that night was heavy and painful
ดั่งทุ่งแล้ง ที่ไรเพิงพัก
like a dry field where nothing rests
ดั่งภูสูง สูงสุดสอย
as the mountain the highest mountain
โอ้ยอดรัก ฉันกลับมา
oh my love I return
ดั่งชีวา ที่เคยล่องลอย
like a life afloat
มาบัดนี้ ที่เราเฝ้าคอย
Come, this is what we await
เจ้านกน้อย โผคืนสู่รัง
the little bird flies back to the nest
นานมาแล้ว เราจากกัน
We parted long ago
โอ้คืนวัน นั้นแสนหน่วงหนัก
Oh a night so heavy
ดั่งทุ่งแล้งที่ ไรเพิงพัก
like a dry field where nothing rests
ดั่งภูสูง สูงสุดสอย
as the highest mountain
โอ้ยอดรัก ฉันกลับมา
My love, I return
ดั่งชีวา ที่เคยล่องลอย
มาบัดนี้ ที่เราเฝ้าคอย
like a life afloat
เจ้านกน้อย โผคืนสู่รัง
a little bird flies back to the nest
ฉันเหนื่อย ฉันเพลีย ฉันหวัง
I am tired, I am weary, I hope UNICEF Concert Album (I think) หงา คาราวาน (Official Audio) Thai PBS Khon Dankwian (Lyrics) Thai PBS ปู พงษ์สิทธิ์ คัมภีร์ Orawee Sujjanon Loso


Flowers from the Garden
ขอมอบ ดอกไม้ ในสวน
I offer, I ask  the flower from the garden
นี้เพื่อมวล ประชา
for the people, the publci
จะอยู่ แห่งไหน จะใกล้ จะไกล จนสุดขอบฟ้า
for you where you are foreverขอมอบ ความหวัง ดั่งดอกไม้ ผลิ
I offer, I ask, for you hope, as in a flower

สด ไสว งาม ตา
Fresh and bright, eyes of beauty
เป็นกำลังใจ ให้ คุณ
to give you encouragement, motivation
เป็นกำลังใจ ให้ เธอ
to give you dear motivation
เป็นสิ่งเสนอ ให้ มา
this is the offering given

ดวงตะวัน ทอ แสง
มิถอยแรง อัปรา
there is a retreat
เป็น เปลวไฟที่ไหม้ นาน
Its a long burning flame
เป็น สายธารที่ชุ่ม ป่า เป็น แผ่นฟ้า ทาน ทน
t’s a stream that’s wet, a forest, it’s the sky, enduring

ดวงตะวัน ทอแสง
there is a retreat(?)
เป็น เปลวไฟที่ไหม้ นาน
Its a long burning flame
เป็น สายธารที่ชุ่ม ป่า เป็น แผ่นฟ้า ทาน ทน
It’s a stream that’s wet, a forest, it’s the sky, enduring

ขอมอบ ดอกไม้ ในสวน
I offer, I ask  the flower from the garden
ให้หอมอบอวล สู่ ชน
to let its fragrance crash ????
จงสบ สิ่ง หวัง ให้สม ตั้งใจ
Something about hope conscientious?
ให้คลาย หมอง หม่น
calm down, chill?
ก้าว ต่อไป ตราบชีวิต สุด
move forward towards life’s end
ดุจ กระแส ชล
like the flow of fresh water (lakes, streams?)
เป็นกำลังใจ ให้ คุณ
I give you encouragement
เป็นกำลังใจ ให้ เธอI give you encouragement dear
เป็นสิ่งเสนอ ให้ คุณ
เป็นกำลังใจ ให้ คุณ
เป็นกำลังใจ ให้ เธอ
เป็นสิ่งเสนอ ให้ คุณ
เป็นกำลังใจ ให้ คุณ
เป็นกำลังใจ ให้ เธอ
เป็นสิ่งเสนอ ให้ คุณ
เป็นกำลังใจ ให้ คุณ
เป็นกำลังใจ ให้ เธอ
เป็นสิ่งเสนอ ให้ คุณ..


Collected notes.

“Wirasak Sunthawnnsi (taj. วีระศักดิ์ สุนทรศรี, ur. 24.07.1950 r. – Bangkok, Tajlandia – zm. 17.12.2021 r. – Prowincja Samut Prakan, Tajlandia) – tajski gitarzysta i wokalista. Jeden z założycieli rockowego zespołu Caravan, dziś określanego mianem kultowej kapeli rockowej Azji Południowo-Wschodniej. Caravan jest muzyczną wizytówką Tajlandii lat 70., 80. i 90. XX w. Poniżej grupa Caravan w nastrojowej balladzie „Khon Phu Khao”. Wirasak Sunthawnnsi (Thai: วีระศักดิ์ สุนทรศรี, born July 24, 1950 – Bangkok, Thailand – died December 17, 2021 – Samut Prakan Province, Thailand) – Thai ski guitarist and vocalist. One of the founders of the rock band Caravan, today known as the cult rock band of Southeast Asia. Caravan is the musical showcase of Thailand in the 1970s, 1980s and 1990s. Below, the group Caravan in the romantic ballad “Khon Phu Khao”.”

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.

Beat Frequency

I thought that I should write something on the development of my new piece, “Beat Frequency”, what its roots are, how it came into being.
I grew up in a musical family. We sang, played musical instruments, I played violin. In order to tune a violin to pitch with a pitch fork or some other stable frequency source you play the violin at the same time as the source. If you are off by 1hertz, so if your pitch fork is for A440 and your violin is at A441 then when the peak of the wave forms happens to hit your ear at the same time it is louder, and when one source is high and the other low, it is softer. This gives the sound a wah wah happening every second. As you tune closer in frequency the wahs happen less frequently.
My father, may his memory be a blessing, built harpsichords. He taught me to tune them. For a short while I could do a reasonable job with just a pitch fork. This is more difficult than it seems because a tempered scale where all the intervals seem reasonably in tune, requires that you actually tune intervals a little imperfectly. Its kind of like walking around a circle with a diameter of 4 feet one foot at a time. When you get to the end, you are going to be a little off, so if you stretch a bit a walk a hair over a foot at a time, no one is going to notice, and you will end in the right place.
I sang. My favorite music to sing was madrigals. They are sung by small groups of people. In my opinion they are best as entertainment for the singers. Singing facing each other in a circle is optimal. In order to do this well there needs to be give and take between the singers each allow each other openings when their singing line should be dominant. You hear this give and take in Jazz or other folk music too.
In my first Art History Class, an overview of Asian Art History, at The University of Michigan, taught by Walter Spink, we were taught about Taoism and its symbolism in Asian Art. The story associated with this was that a man, in tune with the Tao dropped his towel on the side of a river and walked upstream to a bridge where he stripped off his cloths and through himself into the raging torrent. He washed up by his towel where he dried himself off and then walked back to the bridge to get his cloths.  Rivers, and images of water, are often statements about the order, the nature of the universe, of ebb flow, give and take.

Most of us learned prime factoring as children. You take some number and find all the prime numbers that it can be divided by. For example, 165 can be divided by 3,5, and 11. If you have waves a 3,5, and 11 hertz, cycles per second, they will only all come together every 165 seconds. In tuning this would mean that the strong beats happen only every 165 seconds, but that there could be weak beats at multiples of 3×5 (15 hertz), 5X11 (55 hertz) and 3X11 (33 hertz). I use this phenomenon to program the lights so that their effects repeat very infrequently. My math teachers would be happy.
I took electronics in High School. Mostly I learned what was taught. When we got to AC I was very mystified. I really lacked the ability to concentrate enough to gather all that was necessary for understanding at once. I still struggle with this, but I do know what I should have learned back then. It gave me enough understanding to make moving forward with the electronics I need for these lights, and also for ham radio, not too much of a challenge.
I also took computer programming in High School. We did not learn that much, and similar to electronics when we got to assembly language I was mostly lost. But I produced some programs, learned some basics and it has been nice to have this skill. Back then, programs were put onto cards and encoded with little holes that were read by shining a light through them and detecting where on the cards the light past through them. The machines that made the holes were call “keypunch machines”. You hit a key and it punched hole[s for a letter or number]. In general, you put one command, or one program line, on a card.
Our teacher would on Fridays take our cards down to a local university and get them run on their computer. On Monday she would pick up the printouts, the only output from our work, and bring them too us. For all intents and purposes, there were no terminals with video screens for us to use. I did not see one until two years later when I attended a big university.
After leaving engineering school I started doing Ceramics. I was interested in pottery. I was not driven enough by pottery to stick with it, although I did pick up some skill. More than this specific media and product I became interested in designing within constraint. People think of constraints as limitations, but they create a liberation. Without constraint there is no way to start to do anything. This was covered in Robert Pirsig’s book, “Zen and the Art of Motorcycle Maintenance” under the heading of “Stuckness”. Unable to start an essay describing downtown Bozeman, a student thought that they had nothing to say. Pirsig told them to start at the top corner of a particular building. This allowed them to get started. Not only was this a constraint, but a particularly specific one.
I like wood fired ceramic surfaces and also its relative, vapor glazed surfaces. They are most often brown. A colleague who worked in cast iron thought that we should have an exhibition entitled “Brown”. There is an infinite amount of variety in color and room for expression and other content between two shades of brown. The limitation, is not a limitation. It starts a conversation.
My work, my art work, for the better part of 40 years, seemed to revolve around expressing the area of thought between words, pointing out the constraints that language imposes on how we think. What is Function? What is not? What is Functional Ceramics, what is not? What is Art? Where are the edges of these words and meanings? Do they exist? I am not sure that my study of Far Eastern Art, and the need to learn some about Taoism and Buddhism started this inquiry, but it informs it. The world defined by words is illusion. Words are an abstraction of reality as are photos, video and sound recordings.
Starting in the late 1990’s I started making videos about these ideas. The first was about Art History. The definition of Art used in the academy and particularly in Art History is narrow, limited, and ethnocentric. While what is show in Art History course has expanded, it is most still seen through a lens that remains unchanged. Movies continued. There were ones about what Ceramics is, what Art is, and why woodfiring is important. They were really about philosophy, but also about beauty and fun along with other things.
One aspect about many of them is that they had two audio and video tracks (or more). These tracks became dominnent and then stepped back in the same manner as the madrigal music I like, or like waves at different frequencies. They beat. There is and was crescendo, and decrescendo, give and take. I loved playing with the stereo. Two related discussions seemed to capture the thoughts of viewers.
Sometime in 2011 I bought an Arduino. This is a microcontroller development platform, a small programmable computer used for developing microcontrollers for embedding in simple devices like thermostats, drones, three d printers and my lights. I really had no idea what I was going to do with it, but a student asked me how to make a switch turn on a device with some specific timing and this device seemed the easiest way to do it. I got up to some basic speed with the device quickly. I had the right set of skills and experience. The platform, Arduino, was designed to allow, to create a space to learn, allowing non-technically trained microcontroller experts to develop applications.
Lady Ada and Adafruit
Adafruit, run by a fantastic innovator who goes by the name Lady Ada, sells parts and supplies, boards, and really education in part for people using Arduinos. She got started in college. Frustrated by having to wait for electronics to arrive, she stocked parts and sold them to other students out of her dorm room. Its a fantastic company. I do not think that I ever would have succeeded in making work with the Arduino without her and without companies like hers. She manages to have a manufacturing plant in New York City.
The digital revolution has brought an amazing plethora of opportunity. My early lights required that I build circuit boards by hand. My small hand skills are not great. I am not neat and clean in small detail. In the modern world I would be diagnosed with Dysgraphia, and likely some small motor skill deficit. I have managed to survive and flourish despite it. But, one day I just became ill over the idea of building another board to control my lights and said to myself, “whatever the cost, I am going to have these boards made for me”. So like any modern person, I went to Youtube to find out how to do this.
On a Monday Morning I watched 39 minutes of video instruction on using an open-source program for designing circuit boards for production by a factory in China. On Tuesday, I designed my board and was finished before noon. Wednesday morning I checked the design and uploaded it to the manufacturer and made my payment. A week later Wednesday at around 5 pm my 5 custom printed boards were delivered to my door. The total cost was about $13.50 including shipping. I should have done this sooner.
Those were just the boards, and I had to solder everything onto them. Now I am getting most of my parts place by robots. Doing this allows me to not pay several layers of markup on individual parts and is actually cheaper than assembling myself. Also many of the parts are too small for me to reliably solder to my boards with my current skill level and equipment.
The boards are essential screen printed. A block is printed onto both sides of a fiberglass board sandwiched between two thin layers of copper. The board is etched until the exposed copper is gone, leaving copper only where there is a block. Holes are drilled through the board. The board is then screened again with another block and then it is plated with solder including the inside of the holes. Both sides are printed with whatever text or marking you design into the board, the board is tested, cut out, and packed for shipping. When getting robotic assembly, this comes just before shipping.
Etching a circuit board uses the same process as etching a plate for an intaglio print. My boards I am having assembled are small. In this piece they are about 1/2 inch by 8 inches. I am using a 9″x 12″ one sided board that I designed (Maclovio Cantu taught me how to etch the board) that was etched in a bath of ferric chloride. This board is the base that everything else is mounted on. The traces of copper on this big board are decorative, but also constrained by needing to provide power to my small boards. There are six small boards used in this piece, three on the front, and three on back.
I am having some technical issue that I have to solve before I sell work like this. Likely this will involve some design constraints. It is easy for this to seem depressing, a hassle, etc. It is more productive to think of it as more opportunity. Dealing with the constraints causes growth.
Beat Frequency uses six of the twenty five boards I had printed and assembled early in December. I also let the smoke out of one. “Letting the smoke out” really means burning out the parts, overheating chips until they smoke. I hooked it up backwards. The 25 board cost about $130 dollars. They took a full day to get ready for production and are based on the work done on three other boards. The board before them was quite similar.
This board uses a microcontroller called an ATTiny85. They cost about $1.59 and are again available. I would prefer using the ATMega 328P-PU. I have some on order and expect to get them in May. I bought a stack of the ATTiny85’s at the beginning of the pandemic so I would have some. The 328’s are more powerful. One could run the hole project. Instead I am using 4. On the back the top and bottom board uses only one board and the right and left lights on the front are similarly linked.
This short essay [was posted] unedited. Nor did I go through and correct spelling, grammer [(left on purpose)] or other mistakes. I am going to post it before editing, and if needed will correct and encase the corrections inside [brackets]. I did write an outline.

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.


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.


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.