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.