Happy New Year

The fall anagama firing seems like quite awhile ago.  The end of semester work load (mainly on Janelle's shoulders- with help from Vincent) was quite a crush thanks my needing a new left hip.  All has gone well. Many thanks to Janelle and Vincent for filling in.  They are the best.

The was our fourth firing.  We continue to learn a great deal each time.  This firing was no different.  First, we were determined to take this firing to 40 hours wanting more heat work and ash deposit.  We came within a half an hour of our goal. We were able to extend the firing just fine without over-firing the front of the chamber.    As mentioned in an earlier post, we saw the effects heat work in action.

Second, we took a different tack toward getting heat to the rear of the kiln.  Previously, we raked coals from the fire box toward the end of the firing to create room in the fire box for air to sweep over the coals. Create a hotter firebox, then draw this heat to the rear.  In addition to the open airports, we were opening the stoking port to give the kiln as much air as possible.  Air = heat!  This contributed to more heat alright- concentrated in the front of the kiln.  And hot coals at our our feet made stoking tougher and more tiring- not to mention the need to put the hot coals somewhere.

We found that raking hot coals is not necessary at all.  In fact, it makes little sense when the idea is to get as much heat from your fuel as possible.  A lesson I learned when younger (rake as few coals as possible) is taken to the logical end.  So we have made life a bit easier by being a bit smarter and patient.  It's these little things that experience brings.  I especially like solutions that repair more than one problem, in this case- no coals to deal with and moving heat (work) to the rear of the kiln.

We stirred up the fire box regularly to keep the fly ash moving and to keep the surface area of the burning wood exposed to as much air as possible.  This also was a better way to manage the coals.  So patience in stoking and letting the firebox work was the key.

We also used quite a bit of pine bark at the end for color.  I am not sure of the result- willhave to do it again.

We didn't use the Troy body this firing since the clay shipment didn't come in time.  We plan to experiment with it more next time.  Maybe the bark will have more of an effect on the lighter body. I like a darker body, but it would be nice to have a bit of light burning stuff to play with.  I find the bodies that seem popular now like the B Mix seem to be on steroids, loaded with plasticizers.  The Troy body is similar.  Good for simple full forms and great for surface marks and tracks.  I find it difficult to make pieces that demand more from the clay, some tooth (the folded walls I like are too thick- maybe with more time I will get it).

I want to play with some things like lithium wash and soda ash to see what happens.  Making a slip out of the Troy body might be interesting also.  And the old stand-by of Rutile and G.B. is always good.

The Master

We will be posting images and comments on the wood firing shortly. I ran across some images of our man Vincent Clemente, retired professor of art here at PrattMWP, and the dean of potters in the Mohawk Valley. Thought I would share them. He is demonstrating for my sophomore throwing class. At 86, he is still an integral part of our wood and salt firings.

For more information on Vincent, see the May, 2008 issue of Ceramics Monthly.

Salt Firing fall '09

Thanks for this image, Grace.

The weekend salt firing was quick and sharp. Starting it at 7:00 pm Saturday and firing it off at 5:00 am Sunday reminded me of the firings we would do in Oklahoma during the summer. It would get so hot during the day we chose to fire through the night and finish at dawn to beat the heat.

The insulating fire brick (seen in the image) take a beating. We have been able to coat them on the inside (hot face) to keep them from deteriorating too rapidly. The spy holes are another story. Looks like a good spot for castable repair.

The anagama is still cooling some 3 days after...

Have been reading the latest edition of the Log Book . We knew Jack's article was going to be in it. I still find it hard to believe he lost interest in salt firing. The traditional approach to salt can be somewhat one dimensional, true, but vapor has so many variations from ∆ 03 up. It is so versatile. I have fired terra cotta at ∆ 03-3 with great results. In fact, I was looking for a similar surface to the Voulkos' platters while in grad school that lead me to experiment with low temperature vapor back then. Soldner used vapor in raku in the 1970's. There is so much to try. And Jack's excitement when holding pieces from our collection certainly gave you the sense he was still smitten. But as artists, we have to follow our gut as well as our head.

Speaking of raku- it too has endless possibilities if you get beyond the tired stuff of the past 2 decades. Going to commercial glazes is too easy. The "flash" factor is still alive and well unfortunately. Try using darker bodies and spraying on frits and clays and borax and lithium and ochre and on and on...

We are knee deep in a baroque fashion in American ceramics. Nothing wrong with that I suppose, but the band wagon is wide and deep. Always has been. I was a product of abstract expressionism (the last great dominant movement, I think- the post, post, post, modernist era is still up in the air, due to the need to label such movements immediately, sucking the oxygen out of the air) and the far eastern aesthetic which some today may find tired and lacking. But the subtle is permanent, flash is temporary.

Afterburn

After 39 1/2 hours we brought the wood firing to a close. We were able to soak for close to 7 hours allowing the back of the chamber to reach a solid ∆ 9. If there is one human trait that often trumps all others, it is patience. "Heat work," that critical, almost magical element is the reward for letting the kiln do its work without pushing and prodding.

It is particularly satisfying to show students this mystical process, after talking about it so much. The pyrometer and cones in the rear of the chamber confirmed our trust in the kiln and rewarded our commitment to continue stoking.

For our "soak" we decided to stoke to keep the rear at a steady 2100º F (not wanting the front to run away) and let the kiln do the rest. We finished stoking with pine bark for color. We shut it down after reaching cone 9 in the rear with the pyrometer still reading 2100 plus or minus.

Just as the lighting of a wood kiln is quiet and ceremonious only to the degree we want to confer, the end of a wood firing is equally so. Simply stop stoking and close up the kiln. No switches to turn or burners to shutter. The very instrument of all our constant and tiring attention simply winds itself down with no fanfare other than any we might wish to perform in front of it, assuming the energy is still there (and more likely to happen if given some thought before the lighting).

Once again we fired the salt kiln on the last night of the wood firing. Smoke and vapor everywhere. And it would not be complete without a visit from the UFD. They are always gracious and even curious at times. We are always very thankful they show even if we give them a heads up. You never know.

Fall Anagama Firing '09

Just a quick note- we are in the 31st hour of firing the anagama. We are at about 2100 degrees in the back of the chamber and climbing well. Our goal is to get above cone 8 in the back in the next few hours and continue the climb leading to a soak of 6- 10 hours.

More to come...

Upcoming Firings

We will be firing the wood kiln in a few weeks, loading early in the week of November 16. The plan is to start the firing on Thursday the 18th and fire till Sunday evening. We will be firing the salt kiln that weekend as well.

We hope to fire the wood kiln longer this time, getting more heat to the rear of the kiln and more "heat work" in general. When we visited SU last week they remarked how Jack had fired their anagama long and with little air. Makes sense- if you want to get heat to the rear, lengthen the flame. We have been making slight adjustments to that end as well.

SU's kiln has a very deep and tall firebox relative to the ware chamber. Never quite noticed that before. Although it is a hill climber (stepped chamber), the crown is level. Troy brought hardware for setting up a grate in the fire box. There are a number of pros and cons for this. In the case of the SU kiln, it seems that you would get more flame to the crown which would help draw heat up and over to the back of the chamber. You can get fewer ashes and coals as well. But patience is the key. A longer flame helps keep things even. Pots and bag wall placement/height matter as well. I am not sure about the stoking ports to the rear of the (SU) kiln. It seems they are so far back that you are feeding the stack, not the ware chamber. They are talking about creating an air port for the rear stoking port, but it still seems that you might be doing things a bit late in the chamber (ps- Henry Gernhardt, SU Prof., had suggested an air port in the rear when the kiln was first built- I defer to him!). Noborigamas don't have after burners. And the effects of a "check draft" need to be considered.

Feeding the stack has always been a question for me. A long flame does just that. But an even kiln is usually the goal. The trick is to strike a balance. The stack is a tool, not a chamber. But it is fun and dramatic to "candle" the top of the stack. There is so much to discuss here. We have a "secret chamber" between the main chamber and the stack which we have yet to experiment with. Part of the excitement is the variations in approach. Maybe someone has some ideas to bounce around.

We originally planned a grate on our kiln but opted out. We were tired and wanted to get on with it. We also knew of wood kilns without them that fired fine. I think it is something we will eventually try (our kiln chamber does not step up like SU's- our fire box is lower than the chamber; the crown is level). I do think the coal/ash amounts can be managed either way. One of the first things I learned years ago was not to be so efficient in pulling coals from the fire box. It is tempting- but you are losing valuable btu's.

Air is another issue. A wood kiln is the same as any fossil fuel kiln, but the reads are a bit different. For example, a lot of flame at the ports and damper means reduction in a gas or oil kiln, but not necessarily so with a wood kiln...

At SU they use the same phrase we do- "we are just learning about this kiln." Great fun.

Water and clay

I was reading somewhere the other day about water and throwing. The article was about the notion that too much water is bad for the walls of a pot and weakens it. I immediately began thinking about the various "wives tales" that seem to survive generation to generation without skepticism. This is one. Flat out- you can not use too much water when throwing. But that statement makes one important assumption, that you are using good technique.

The explanation goes like this- the walls of a pot are built as a result of compression or pinching the clay between the fingers or any other relatively narrow point of the hand (I have known potters to use the knuckle or thumb, for instance). This means the compression points must be directly opposed. You can't have compression any other way. In doing this, you assure the wall is as strong as possible (tight) and as such, it just cannot take in water. I suppose you might be forcing a bit of h2o into the surface of the wall in any given pull. But you are also clearing the wall of water as you bring your fingers up (the pull). The wall is always dryer beneath the pull. The key is compression (we will make the distinction between a compression pull and a shaping pull in a later post).

Here is how wall weakness begins- if you lose compression you are stretching (tearing) the wall (in tension) which is literally opening the wall to water penetration. You lose compression by letting the inside contact point migrate above or below the outside. The wall is weakened from the stretching. Water will exacerbate this weakening, but it is not the culprit.

The second important point is that water is used to lubricate. And slippy water is a better lubricant (to a point) than fresh water. So always add water to your water bucket rather than starting over with fresh tap water. Throwing slip is high(er) in solids which do not penetrate the surface of the wall (in fact they align parallel to the wall, which helps lubrication). As the throwing slip loses its ability to "sheet" the wall, add fresh water to it.

Clay is often used to protect surfaces like a cellar wall from exposure to surrounding ground water. The clay is compacted in and around the basement. But another test is easier to carry out. All potters learn very quickly that dry clay sucks up water very fast. Remember the pot that got to dry to trim? Putting green ware in water will leave you with a dissolved wall inside of five minutes if not sooner. Do the same thing with leather hard ware and you find the time it takes to soften is longer. Water moves through clay by capillary action. But you need capillaries. The denser the clay (wet and well wedged) the smaller the capillaries.

So the problem is not directly the water, but losing compression on any given pull. This happens when the fingers are not directly opposed, creating a tension or stretching of the wall as it is "folded" through the fingers. This allows water to infiltrate the wall and the wall to weaken. From a teaching standpoint, the rule is still to use plenty of water. Learning to throw is tough enough without having to fight the drag that dry throwing creates.

Finally, to throw without water is no doubt a virtuoso performance. But I can't help but feel the walls straining between my fingers, torquing at a greater rate than lubed clay and being stretched unmercifully. Having said that, I still am amazed at the skill some possess. I remember the great California potter, Michael Frimkiss demonstrating his dry technique many years ago at Supermud at Penn State. What a touch. But I think he could do it wet as well as he could dry.

Add to this discussion, please. I know there are other variables like grog content and plastic clay content, form, shape and wall structure. The order of wall construction (top/down, axis/out) is another topic very much related to this. Would love to hear them.

Jack's Visit to Campus

We were honored to have Troy, Peter Beseaker and a group of SU students come to our campus yesterday to see the collection of White's Pottery housed in the Fountain Elms section of the Museum of Art. These pieces from the Utica pottery made during the 19th and very early 20th century are important to understanding the need for potters during that era and the skills they possessed. Jack's love of early American crocks is noted in his first book on salt fired pottery published in 1977. Assistant Director and Curator of Decorative Arts Anna D'Ambrosio hosted the visit, providing us a rare opportunity to view up close these important objects.

Jack's comments revealed his underlying interest in the working conditions of the day and the story behind the potters that made these pieces. Peter's questions were often about the origin of influences for the forms and decorations. My interest centered on how they were fired and how much concern about kiln affects these potters had. The answers to all questions might be found in one simple fact- this was commerce. These were business men making very practical decisions, with the benefit of highly skilled artisans, in response to the market. White's Pottery and others like it had a relatively short existence, being largely replaced by glass in the early to mid 20th century. But American potters of today can look at these American "unknown craftsmen," (to borrow Soetsu Yanagi's term for the potters of the Mingei era in Japan), with much to respect and appreciate. For me, the simple use of salt for glaze finish, borrowed from the German potters of the 16th century, unintentionally nurtured an aesthetic we value today.

We also enjoyed the group's visit to our shop and kiln shed. The clay department is housed in a 19th Century carriage house built by the Williams family, the main benefactors of Munson Williams Proctor Arts Institute. Designed by Richard Morris Hunt, who also designed the base of the Statue of Liberty, the building is an architectural force. (Again, I think of the very few degrees of separation contemporaries often enjoy with others in the field and with history.) The sturdy construction of brick and timber reflected an affluent response to a common need, in this case, the mode of transportation of the day- the horse and carriage. The interior enamel glazed brick is ironically appropriate for a carriage house turned into a pot shop. There was a system of elevators for carriage storage on the second floor. The horses were kept in the north bay of the carriage house with the attendants bunked in a small room to the south end that included a beautiful terra cotta fireplace for the cold winters of central New York. Quite a building.

Unfortunately, paint covers much of the enamel brick in what is now the wheel room. It makes me wonder what some people were thinking. The enamel was not only beautiful, but practical. On the other hand, the fireplace, uncovered (irresponsibly?) as soon as I was aware of it, has been, once again hidden by a shelving unit. I have mixed feelings about that. But our storage needs in the end serve to protect what certainly is a valuable architectural feature.

Over the years, I have done my best, when suggesting functional improvements in the space, to retain the building's character. I think the unique nature of the carriage house is more readily apparent today. A small victory when compared to the damage done to classic main street buildings in almost any community in this country, a result of "modernization"- the urban renewal disasters. Our structure remains a wonder. We are truly lucky to work in such a historic setting. And happy to share in the story behind it.

Troy Workshop

The Jack Troy workshop and opening was quite a treat for all. The workshop turnout was light, I thought. But some of our students were able to attend. Their response was enthusiastic and energized. Jack did a great job with his demo and stories. It is always a pleasure to watch a master at work. Jack's interest in history, literature and writing gives his work and workshop a full and grounded sense of self.

I learned a good deal of what I know from attending such workshops when I was younger. I remember writing, some years back, notes to myself after watching and listening to each new artist. It became evident that all of these masters in the field were saying the same basic things about working and learning. The vocabulary, expressions, and stories from each reflected the range of personalities. But common threads certainly were evident. Listen and you will hear exactly what I mean. I still leave workshops with my head full agreements and (with years under my belt) contrary notions. It is always worth the time.

A side note- the degrees of separation can be very few. During the gallery opening I noticed Jack greeting another fellow as though they had not seen each other for some time. At first, I thought this fellow was a collector I know from the Syracuse area. But his air was professorial, something those of us of a certain age and from the academic world might recognize- the greying beard, the tweed walking hat and the confident entry to the gallery. He looked very familiar, but I could not place him. Then, as we were leaving the gallery I overheard him introducing himself to a young lady. Sure enough it was my former painting professor Steven Barbash. As it turns out, Steve, at one time, was the department chair at Juniatta College and was responsible for hiring Jack to teach clay there.

Great to see you again, Steve.

We are looking forward to Jack visiting our collection this Wednesday.

Jack Troy Workshop at SU

Jack Troy will begin his residency at Syracuse University this weekend. He will conduct a two day workshop (open to the public) on Saturday and Sunday. An exhibition of his work will open Saturday evening (Oct. 17) at the Gandee Gallery in Fabius, N.Y. He will spend the next few weeks making work and preparing for firing the SU anagama. The tentative firing dates are Oct 26,27,28.

A potter, teacher and author for over 50 years, Troy is known for his work in salt and wood. For biographical information go to www.jacktroy.net.

He will also be visiting PrattMWP during his stay to see the our collection of local mid nineteenth century salt ware made by White's Pottery (N. White Pottery and sons, Utica) and others. In his 1977 book on salt firing, Troy mentioned the Utica pottery, which found some success here thanks to the Erie Canal.

This will his first time seeing our collection in person. We are fortunate to be a small part of his visit.

Kiln Wash

I was just reading the Oct.3 newsletter from CM on kiln washes. John Britt's information was right on and common knowledge for the experienced (or experimentally leaning). It was Arise's comment that I found interesting. We have been wetting our shelves before applying a fresh wash for a few years. Similar to applying mortar to a brick. And the idea of grog in the wash sounds good. Be careful about what grog you are using, though. Calcining is good, but there are many materials that may require less work. Some years back, we used (and are again experimenting with) pyrophylite (nothing new, as others have mentioned it). It is a "high silica, natural alumino-silicate," (Robert Tichane- Clay Bodies, 1990). The key is the low thermal expansion. There are a number of materials that fit this description. I recall Steven Kemeneffy using kyanite, a material in the same family, in his raku body.

(I believe Soldner used talc in his body. This material is a bit more complex and the reasoning behind using it for raku is the somewhat questionable theoretical lowering of body expansion.  Don't use talc in a wash though!  In an engobe would be ok. This is for another time though.)

So, low expansion materials with a bit of binding material (like EPK or glomax if you prefer calcined clay) and your on the right path. We also use a roller rather than a brush. I picked this up while at Syracuse University. If you get the right nap, you get a textured surface with peaks and valleys, which seems to decrease the shrinkage (which is a lateral thing- but, you would think a brush stroke would align the clay particles parallel, which would be a good thing... over-think, sorry- low shrinkage is the key). Multiple applications will work.

At SUNY Cortland, I recall the notion of starting with a thin wash first and then apply thicker coats. We may have picked this up from Rhodes, I don't remember. But this means having more than one bucket of wash which is a hassle. We roll on a few coats of the same thickness, not letting the previous coat get too dry. For salt we would use silica dusted on the shelves. Straight silica is much different from the silica contained (combined) in a clay (like fire clay, stoneware, ball clay) or a clay body. The salt vapor alone just isn't enough to flux the silica. Has to do with eutectics. Anyway, we never had a problem.

The idea of employing a bit of flux is exactly what lead us to using our mix (see previous blogs) of kiln wash in the salt kiln on the insulating bricks after a few firings. The wash fused to the walls. So far, it is "sticking" quite well. But the jury is still out. We are getting a fair amount of peeling. So our experiment may prove more work than we want. I feel that some of these ideas are not necessarily "new" (few ideas really are), but are being rediscovered all the time, using "new" materials or new technology. Keeps us on our toes! The old "Ceramic Industry" magazine would publish a materials issue every January. Priceless. Now you can find it all on line very readily.

A funny story about this fusing thing. I once had an assistant (a very long time ago, in a far away place) who washed the salt kiln shelves with feldspar by mistake. All those similar white powders! It meant long hours of grinding. The idea of fusion is a good one, but...

We have some concern about the nitride bonded shelves that has nothing to do with moisture. We love them... But glaze does not peel off these shelves as described elsewhere. It seems to soak into the shelf just enough to cause problems in subsequent firings. We are finding this to be a real problem with porcelain. We are waxing the bottoms of porcelain with alumina in a water based resist to be on the safe side. In salt firings, we are dusting these shelves with alumina (oxide or hydrate) and using wadding on the bottoms of pots. Over-kill, but it works. We store n.b. shelves horizontally (with shims as spacers) between firings to keep the alumina in place (it is expensive). With care, we get a number of firings without re-dusting.

We have also applied wash (pick a recipe) thickly and used a grooved scraper to create peaks and valleys. This held up very well in the salt kiln and in some cases left a nice mark on the bottom of pots. It seems to be best, however, to dust the shelves, plain and simple.

Student Salt Firing-10/09

Good job on the firing, guys. The test rings showed good glaze build up. I think the results will be very good.

Every firing is different! In this case, the amount of flat ware lead to tight vertical stacking of the shelves which caused temperature zones in the kiln, preventing the stack from drawing early in the firing. This happens because the shelves baffle the movement of heat throughout the kiln, especially down to the flue. Heat naturally rises and collects at the crown of the kiln. We had red heat at the top while the flue was dark. We also had back pressure at the ports, indicating a reducing atmosphere. This is a potentially serious problem early in the firing which can lead to "black (or carbon) core" in the clay walls. A piece reduced too soon will be "punky" and fragile. It will lack that familiar "ring" when tapped. A pot with a dull thud and no obvious cracks may mean the walls have black coring.

The solution was to induce draft by starting a small fire in the stack. Just lighting a piece of paper and dropping it through the damper plate slot does the job. You can immediately feel the pull of the stack by placing your hand at the damper opening. You now have draw and heat will be pulled to the bottom of the kiln. In the interest of safety, you can place a lighted match or candle at the opening. You will see the air being drawn in.

An opening in the stack is known as a "check draft." The stack pulls in cooler, outside air through the check draft. But you should be very careful when putting your hand near the stack. More importantly, putting your hand (or face!) close to any chamber port is never a good idea no matter what the temperature of the kiln. For ports, the "stick test," placing a stick into a spy port and watching to see if the resulting flame at the tip is drawn in or is pushed out, is best to determine draw or atmosphere. It's a handy tool since it works in some situations that don't provide normal visual cues, like the bottom spy port.

Down through the years I have seen kiln plans with "mouse holes" at the base of the stack. They are there for inducing draft just as we did. But if the stack is tall enough, an opening at the base should not be needed (fun to include in designs for teaching purposes, though). And placing the damper in the stack provides an incidental advantage, as we found out.

Yes, you learn a lot with each firing. And yes, it is complicated at first. With experience you will learn to read the kiln. The senses will tell you everything! I like to hear comments like "there isn't as much vapor from the stack this firing," or "this firing seems faster." Being aware and paying attention to detail is important. Keep your head "in" the kiln and your senses alert to what is going on around it. And take good notes (I should talk!).

Good craic as the Irish say. I am anxious to see the results.

Troy at SU

Jack Troy will be at Syracuse University this month (Oct. 18- ?) for a workshop, show and firing the SU anagama. We will be posting more as the dates approach.

Salt Firing

The purpose of this series of postings will be to provide guidance and a bit of commentary on fossil fuel kiln firing, starting with salt (or soda) firings. Later posts in the series will be on wood and reduction firings, kiln design ideas, and experimentation. Design and aesthetic considerations of the work being fired in such "atmospheric" kilns will be discussed. Feel fee to add or remark on the ideas presented.

A general overview or outline for firing the prattmwp salt kiln can be found at my blog, bryanmcgrath.blogspot.com. But the rest will be found on this site. Please note that we are discussing the firing of our particular kiln. It is a 40 cu. ft. (stacking space) sprung arch downdraft made of insulating fire brick (IFB). We do not use soda as a rule. Straight salt is less polluting (more on that in a later post) and easier to use. We will organize the firing as follows-

-preparation and starting

-firing (oxidation/reduction)

-salting/soaking/cool down

Preparing the kiln-

Before loading the salt kiln a few important tasks need to be done:

- Make sure the kiln is "clean." Clear debris from the fire box, especially in front of the burners. Also, make sure any large drips of glaze, or in our case brick "peelings," are removed from the arch (more on this later). It is impossible to keep pots completely safe from shelf drippings or other flying debris. Sometimes these accidents add something pleasant to the work, sometimes not.

- Check the exit flue for obstructions and deterioration of flue supports. Be sure the floor and bottom shelf posts are in good shape. It can be hard to predict the failure of kiln furniture in a salt firing. A visual check is often all you have to rely on. You will get better with experience. The risk/reward (or failure!) equation is always a factor.

Most salt kilns require repairs more often. It is best to do the inspection and any repairs well before your firing date. Many repairs will need time to cure. Castable refractory is the best material for filling in holes, cracks and creating areas needing support like portals. We use a commercial mix. You can make a castable from scratch as well. Many recipes are out there. Repairs can sometimes wait a firing or two, but the sodium vapor corrosion is cumulative, so routine inspection after every firing is best. It should be noted that a kiln made entirely from castable may require the least repair work during its life. Factors in deciding on what type of kiln to build will have to wait for another time.

We wash the kiln walls with a commercial mix called "Plistix 300." It is a refractory wash (high in zirconium and alumina) that protects the insulating bricks. We add water and a small amount of kaolin (EPK) to the mix as a binder. Then we brush this wash on the walls (and the arch with crossed fingers) every few firings.

A note is needed here-

As mentioned above, we use insulating fire brick for most of the kiln wall and arch (hot face and outside). This is usually advised against in the books. Being a school, we (read "I") decided to experiment using IFB for the hot face or interior walls. We did encounter a few somewhat expected glitches. After seeing what actually happened to the bricks- they soaked up salt readily and began to glaze over (with the pots left very "dry"). With hard brick this glazing over is normal and part of the kiln aging. These, however, were being eaten away quickly (not good for the high "R" value of the walls- the reason for using IFB in the first place). Our solution was to wash the walls with the Plistix mix and watch the results. In fact, firing a few times before applying the wash was a benefit. The wash fused enough with the slightly glazed insulating brick to eliminate the concern about flaking. The arch is an issue as we get some flaking or peeling. But a hard brick arch would have some dripping. The flaking is definitely (always) worse on the pots than dripping.

We also lined the firebox, ports and the strike plate at the rear of the fire box with the castable. So far, so good! The time and effort to reach temperature has been fast and easy (we have over fired it a few times!) and the results are great. With some trial and error, the result is an efficient kiln, great results, albeit a bit more maintenance (mostly from rebuilding the parts that take the most heat and corrosion), but worth it. I believe this to be a good solution for schools (or anyone) especially since the firing schedule can be compressed to accommodate busy student (con't. ed.) schedules.

- Finally, prep the shelves. We use a combination of silicon carbide shelves (heavy) and the newer nitride bonded shelves. I have done any number of things down through the years to protect shelves and pots. Dusting with silica; washing with a silica/kaolin/alumina slip thickly applied and then grooved with a notched spatula; dusting alumina (oxide or hydrate) over that (on older type shelves). Now we simply dust all shelves with alumina (a bit expensive, true) and stick a marble size ball of high alumina wadding (using liquid wax resist) to the bottoms or feet of the work. When needed, the shelves are scraped down, then a fresh wash and/or dusting is applied. We are currently experimenting with the nitride bonded shelves. We will report when we have some results.

With attention to the kiln condition and castable in the right places, our kiln should last as long as a hard brick kiln, but probably not as long as one with wash on the walls. But I think the benefits outweigh a longer kiln life (if true). It is an experiment- so we will see. Anyone with experience, or ideas pro or con, please add to the discussion!

Our students will be firing the salt kiln for the first time this semester on Oct. 3. We will give an update on the results.

Next- the pots...

Welcome to the PrattMWP ceramics site!

We will be using this site to give information and news from the PrattMWP ceramics department. Everything from images of current student work to firing instructions and to news updates on local events, firings, shows and other blogs and sources of information. First on the agenda is the firing of the PrattMWP salt kiln as promised in my personal blog. Hope you learn something new and improve your firing skills.