Monthly Archives: June 2023

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.