SPEAKING WITH GLAZES, PART 2

A “glaze” in ceramics is a covering of glass on the surfaces of a ceramic object. Although that might sound straightforward, there can be a hidden world in those surfaces. There are many technical publications on the subject of glazes and this is not one of those. A potter applies glaze to a pot. That glaze consists mostly of naturally occurring, mined and processed minerals. Then she puts it in a kiln and brings it to a certain temperature in a certain atmosphere at a certain rate of temperature increase, then cools that kiln at a certain rate for particular effects, all contributing to the end result. Many glazes are very “forgiving”, they will turn out how they are “supposed to” with not much regard for all these firing variables except the final temperature, more are less. There are many reasonably attractive, predictable stable, well behaved glazes available, but most readers might agree that almost all are, well, a little boring, in and of themselves.

 

 

 

Traditionally, art scholars have had a hard time describing exactly what “art” is ( Adajian, Thomas, “The Definition of Art”, The Stanford Encyclopedia of Philosophy), but a common thread to all definitions is that all art is “man made”. I am going to try to unravel that thread by claiming that the use of ceramic glazes which may depend on chemical events uncontrolled by the potter are nevertheless an art form. The most interesting glazes are more fickle, the finished product catches phase changes from amorphous to crystalline, there are segregation of colors and textures that tend to be unpredictable, and glaze flaws are endemic. This is a phenomenon that chemists call “phase separation”, that magic area between liquid, solid, crystalline and amorphous, that is captured when the glaze is “frozen” by the cooling of the kiln. The potter is not doing all the creation, she is depending not only on the makeup and preparation of the glaze, but also on partly random events, controlled chaos and the behavior of melted minerals in an imprecisely controlled environment. It is a little like just accidentally on purpose being at the right time and place to see a rainbow across a river canyon. Is that act “art”, with respect to the observer alone?

 

 

 

Is not appreciation on the part of the observer half of what art is? Some people appreciate a sunset and others do not. Is that appreciation of the sunset part of the phenomenon of art, just as is the appreciation of the Mona Lisa on the part of the observer? Underneath it all, though, there must be some family of inspiring or insightful thoughts and sensations that is shared by man-made and natural phenomena. What is really different about the two experiences, other than human ego (the illusion of being a separate entity from the rest of the cosmos) of the observer and the “maker”? Much of art in the West is still centered on the ego of the individual, commerce and social class. Michelangelo was a great artist, Picasso was a genius. Andy Warhol was…, well I can’t say, but he is interesting, and worth money! The “artworld” is part of modern language, meaning those experts who define and create “art”.

 

 

 

 

 

Our very bodies, including our brains are made of substances (atoms) that were formed in distant stars, long ago. There is nothing special about the elements that make up our bodies, and the elements of a glaze were made by the same process. The elements, compounds and life evolved and forged what we are and everything around us. We are, almost without doubt, either an accident or an inevitable consequence of a much larger reality. Each of us is a biological being, with a history of at least 13.7 billion years, if you believe the scientists who have been studying this for only the last 100 years, which I do. We are also social beings, we must belong, be shaped by and shape others, survive with others, not completely unlike ants, honeybees and wolves. I do not intend this as any kind of mystical statement, it is just an understanding based on the best current evidence.

 

 

 

What Purpose does art serve? It serves to create a connection between the observer and a phenomenon. It could take the form of aesthetic delight, triggering curiosity, insight, understanding, something that has value to the observer. This connection can be a man-made entity (art) or something in nature. The difference is only in our egos as humans, competing for status within a community, which is part of our nature. On the deepest human level, we are forced by this nature to compete for status among our peers, and in a very fundamental way that is what the modern “artworld” is all about. If Paris Hilton buys your vase, you are an artist, if Joe Sixpac buys your mug you’re a vendor. You and I may not like this, or maybe we do, but tell me how this is not true at the beginning of the 21st century.

 

 

 

What really counts in these experiences, in my opinion, is that precious connection between the observer (Paris Hilton or Joe Sixpac or me standing in a river canyon) and the object (The vase, the mug, the rainbow). Can anyone explain to me, without reference to human ego or commerce how any of these experiences are fundamentally different from one another?

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A WAY TO TRANSFORM LOW IRON BENTONITE FOR USE IN PORCELAIN

A WAY TO TRANSFORM LOW IRON BENTONITE FOR USE IN PORCELAIN

About Bentonite
Bentonite is a clay of volcanic origin widely used in the ceramics world as a suspending agent in glazes and as a plasticizing agent in damp clay bodies. Most of the bentonite available on the market today is “Wyoming bentonite” or sodium bentonite, and is characterized by extreme plasticity, the ability to hold in suspension several times its weight in water and high iron content (4% to 8% Iron Oxide). Any reasonably pure good quality sodium bentonite will dramatically improve plasticity of a throwing clay body in amounts between 1% and 5% of the total. One downside is the high iron content, which causes a yellowing or graying of high fired porcelain. Fired to cone 10 Wyoming bentonites usually melt to a coarse dark red/brown expanded glassy foam mass and one has to wonder if this melting property might have a negative effect on the finished fired pottery clay as well as a detriment to the color, particularly if it is not finely dispersed into the clay body.

Another bentonite, less widely available commercially but more common in nature is calcium bentonite also called “fuller’s earth” or “southern bentonite”. Unlike its sodium dominated cousin, calcium bentonite does not impart much if any plasticity to clay bodies, holds a fraction of the water, but usually has a much lower iron content, as low .5% Fe2O3 by weight. Bentolite 10-L, a product from Rockwood Additives is one example of a calcium bentonite that is widely available to potters.

The most effective inorganic plasticizer for porcelain is hectorite, a magnesium silicate whereas true bentonite is aluminum silicate. Hectorite is more plastic and holds at least twice as much water in suspension than the best sodium bentonite, and often has the advantage of low iron content, as low as .35% to 1.2% by weight, and does not foam when fired. Hectorite is rare and much in demand for many consumer products, and is therefore very expensive. It also introduces magnesium and small amounts of lithium, and has varied amounts of calcium carbonate (between 10% and 20%) as an impurity. There is a synthetic hectorite on the market, Laponite, which is extremely pure and slightly more effective than the naturally mined products, but is far more expensive than the purest natural hectorite. Hectalite 200, Macaloid and VEEGUM-T are all hectorites.

Making “Bad” Bentonite Into “Good” Bentonite
All true bentonites (aluminum silicates) have varying potentials for what is known as “cation substitution”, where alkali molecules like calcium and sodium exchange places on the surface of the clay crystals, altering the properties of the bentonite in question. Sodium bentonite and calcium bentonite are not really different minerals, but the proportion and location of alkali molecules, particularly sodium and calcium, on the tiny individual bentonite crystals determine its salient properties. I like to think of calcium and sodium ions as analogous to genes in biology, so here sodium is the “gene” that imparts plasticity to the final clay body. Calcium just doesn’t cut it. Cation exchange can dramatically improve physical characteristics that are very important to the potter, namely plasticity and water holding capacity.

Calcium bentonite can be easily “transformed” by the studio potter to sodium bentonite by the process described below. The specific quantities shown are for illustration, and may vary according to the particular bentonite you are using. The process can be scaled up or down to produce any amount of activated bentonite. This process has been used for decades in industry (for things like drilling lubricant and lining ponds), but I could find no publications for its use in ceramics, although it certainly works for me. I present it like a recipe, it’s a little like making soup, but much easier.

A Recipe to Transform Bad Bentonite to Good Bentonite

Ingredients:
500ml water (more or less)
100 grams calcium bentonite, Bentolite 10-L (exactly)
3.5 grams soda ash, Na2Co3 (exactly) (do NOT use bicarbonate of Soda, NaHCO3 )

(1) Place 500ml water in a container and add 3.5gm soda ash (Na2Co3) and mix until it is completely dissolved. You can vary the soda ash in subsequent trials to see which works best, keep the samples for comparison, but 3.5% has worked best for me.
(2) Add 100 grams of calcium bentonite to the 500ml water/sodium solution and mix well with a small power mixer. The reaction should begin immediately, and may take a couple of hours to complete, but will usually take just a few minutes. The result should eventually be a yoghurt-like gel almost identical to natural sodium bentonite with the same proportion of water. As a control, mix a separate container of 100 grams of the same calcium bentonite with 500ml water without any additions; the difference between the control and activated versions should be obvious and dramatic.
Using the same process one can add 2% lithium carbonate (Li2C03) instead of 3.5% soda ash, which makes an even more effective plasticizer. Lithium carbonate is sparingly soluble in water, and no more than 1.3 grams should be added for each 100 ml water used, because the lithium must be dissolved in water to change positions with the calcium molecules in the calcium bentonite crystals. Both additions leave a small amount of calcium carbonate in the new bentonite, but I don’t worry about it, and neither should you, although keep in mind it will make your clay body slightly more vitreous.
In order to obtain a powdered form of the newly activated bentonite it would be necessary to dry and grind it, which probably discourages commercial production and is unnecessary from the potter’s point of view. Most manufacturers recommend you first thoroughly age and power-blend powdered bentonite/hectorite with water before adding it to clay or glaze and potters would do well to follow this advice. By using the bentonite activating method described here you’ve already done that mixing and aging and all that is left is to add your powdered white clay body ingredients to it and mix well. See Dave Finkleinburg’s article in the December 2010 CM for some ideas on how to mix your own clay.

SPEAKING WITH GLAZES

When I do glaze tests I am in a sense “prospecting”, looking for whatever reflects some property of nature, including the eye and the psyche, something that can relate to in a positive way, a sunset, clouds, water running through a stream, reflecting light, mineral formations, rocks, skins, bark of diverse trees, leaves, metallic colored insects, wings, dragonflies, snakes, shadows and light, anything that man did not make, water sculpted rocks, moss, lichens, cracks in anything, decomposition of any kind, sparkle, movement, texture, glow, rusted metal, decayed wood and twigs, feathers, animal tracks, dirt, sand, sand on an ocean beach or mountain stream, waves, ripples in the sand from the moving water, the way tree roots grow, the branching of a tree, the branching of a watershed, a child’s wonder, the coat of a new fawn, the face of a hummingbird mistaking my bloodshot eyes for a flower, the skeleton of a leaf, a bear, a mouse, tendrils of life, shooting stars, stars themselves, star-filled dark skies, moon, sky at daylight, sky at noon, rainbows arching the sky, rainbows in a cloud, rainbows in a mist from a garden hose or stream spray, yes, you can have a rainbow without the rain, feelings of love, of mystery, in nothing more than melted glass on clay.

SOME GRAMMAR OF GLAZES

The glaze can be “crystalline”, that is the eye can see the physical structure of the atoms of the mineral formed in the cooling of the glaze, but this is usually only successful when the crystals are imbedded in a smooth amorphous melted non-crystalline glass (glaze) so the crystals will stand out and be visible, or are framed by a different appearing surface, although the glaze does this by itself, a chemical, heat and time dependent process. These crystals can be mere specks, tiny clouds, patches of iridescence, or large almost ostentatious landscapes. I do not use technical chemistry in my calculations or experiments with glazes, but rather use trial and error based on past failures and successes. I do take great care, however to precisely measure and record the various materials used in each glaze. I learned this approach from Richard Behrens, who use to write a monthly column for Ceramics Monthly many years ago. Mr. Behrens was a trained chemist and also a potter. I took a series of classes from him in the early 70’s in Berkeley, California, and he repeatedly advised not to use formal chemistry in developing art pottery glazes, but to use trial and error and keep notes, and that is what I’ve done ever since.

A word of advice to fellow glaze students. There are no magic glaze recipes. You can use many, many published formulas, but the results are going to depend on many variables, including the clay you use, the thickness of the raw glaze, the method of application, the batch of materials you actually use, the fineness of the materials, the exact temperature, the rate of temperature climb, the rate and timing of cooling and dumb luck. There are attractive, “nice”, forgiving, well behaved glazes out there, but most of these tend to be boring, in and of themselves, in my opinion. When you consider how many elements, compounds, material qualities, firing and application variables available to modern potters, there are probably as many possible glaze statements as there are particles in the observable universe. Think about how much we can say with just 26 letters of the Greek alphabet. Nature and technology has given us far more possibilities than the artifact of conventional language.
SOME PRACTICAL CONSIDERATIONS

Overlapping raw glazes will usually create even more fluidity when the right temperature is reached and some parts of this “run” will contain unique and often unpredictable effects, some amorphous, some crystalline, some clear or opaque, somewhat like miniature landscapes. Almost all of the glazes I use are “fluid”, that is when they are fired to maturity they will creep down the side of a pot, often partly pooling at the bottom, more so when more than one glaze is used, so I make a “firing pedestal” for each piece to collect the overflow, then remove that pedestal after unloading the kiln and grind the foot clean. I recommend the following recipes for making your own clay for pedestals:

Ball Clay (OH-5 is plastic, but any will do)………………40%
Fireclay (NOT Lincoln, not refractory enough)…………20%
silica (200 mesh)……………………………………………………40%
Sodium Bentonite (optional)……………………………………plus 1% to 2%

Mix well into a slurry and dry out on plaster bats. Mix the bentonite first, very well in water, if you use it, then add the clay, then the silica, mixing well between each addition. This formula, or something like it works well because it is soft, fragile, brittle, and has an extremely high coefficient of expansion, and usually will just break away from the foot of your pot and not crack the pot itself or chip the foot when the kiln cools off. It is a very poor choice for actually making pottery, so mark it clearly.