OVERVIEW:

The pieces you see here are all high-fired stoneware. They are impervious to water and can be left outside year-round without being affected by the weather. The clay I use is mainly stoneware thrown on a potter’s wheel. The vases are made in one piece. The lanterns are made of separate pieces and are attached when partly dry (leather hard). Decorations and alterations are also done at this stage (very evident in the sconces). The pieces are then slowly dried over a week and fired in a gas kiln or electric kiln for about 8 hours to Cone 06 (a ceramics term for 1841oF) - the first, or bisque firing. The kiln is then cooled for about 8 hours. Until the bisque firing pieces are extremely fragile and the slightest bump or shock will chip or shatter them. After the bisque firing they become durable enough to be handled. The bisque firing also causes a chemical change in the clay and it will no longer revert to its soft, workable state when wet. Next, an aqueous suspension of a number of powdered products, the glaze is applied to the pieces. Then the pieces are gas fired again, this time to Cone 10 - 2300oF. Each glaze firing also takes about 8 hours. Cooling time is also about 8 hours.

FORMING: Kneading Centering Pulling Use various tools Forming use various tools Trimming use various tools Drying Trimming Decoration Final Drying

CLAYS: There are many types of clay. The most simple of these, and those used by primitive societies, are mined from the earth and used with no processing. Beautiful results can be obtained from these clays. Because of impurities and the inability to rely on a consistent formulation (and therefore consistent properties) however, they are rarely used in production studios.

Consequently, most clays are combinations of compounds. These include purified clays mined from the earth plus compounds to make the clay more plastic, change the point at which it vitrifies, alter it’s color or texture or alter it’s handling properties. The mining process can be accomplished by deep mines, open pit-type mines. Many clays can be collected in small quantities from the surface of the earth with little disturbance to the collection area.

Various clays ‘mature’ or become vitreous (glass-like and impervious to water) at different temperatures. This ranges from very low temperatures Cone 06 with clays such as earthenware and Terra Cotta to clays that mature at comparatively high temperatures such as stoneware and porcelain. Different clays are used because of their properties. Some are easier to shape with the methods being used or hold certain forms better. Some give a finished surface more suitable to the purpose of the finished piece. I chose this particular stoneware for the garden lanterns for its color and durability after the final firing. This stoneware also has qualities that help hold the form of large, thin pieces like the vases.

Some general categories of clay are Terra cotta, earthenware, stoneware, porcelain. People are familiar with these because many red-colored flooring tiles are made of Terra Cotta; clay pots for plants are made of earthenware; much dinner ware is made of stoneware and fine china, toilets and sinks are made of porcelain. Many variations to each type of clay can be made by the artist so that the clay they actually use may not fall into any definite category but may combine qualities of many categories. Contrary to some beliefs, stoneware has nothing to do with stone.

DRYING: All clay objects must be thoroughly dried before they can be fired. The two major stages of drying are 'leather hard' and 'bone dry.' When just created, a thrown piece is usually too wet to stand much handling. Ceramists usually wait until the clay has dried to the point that it has the quality of leather before they add handles, other attachments or do any final trimming. After any final work, the piece is let to dry slowly and completely so it can be bisque fired. Ceramists say the pieces must be ‘bone dry.’ A piece that is not adequately dried will explode if it is fired. The water remaining in the clay will be turned into steam by the heat in the kiln. The steam cannot escape through the clay fast enough and forms steam bubbles inside the clay wall. Since the clay is weak and fragile in this state, the pressure of the steam bubbles blows the clay apart allowing the steam to escape. The force of an exploding piece can shatter nearby pieces and produce a disaster in the kiln.

GLAZES: The glaze on a ceramic piece is really a thin layer of glass. It has two purposes. The first is to make the piece even more impervious to water by coating the piece with a thin layer of glass. The second is the obvious decorative quality. As with clays, glazes ‘mature’ at different temperatures. A glaze must be selected for each piece that will mature at the correct temperature and provide the desired decoration. The glazing process, applying glass forming substances to the surface of the clay object, is almost always done after the bisque firing. Glazes are almost always wet - the consistency of pancake batter - when applied. There are many ways of applying the glaze from brushing it on to dipping, pouring and spraying. Any number of other tools may be used to apply the glaze. The object is to get a coating of glaze on the object that will produce the desired effect. Some glazes require a thicker layer than others. Some will produce different final effects depending on the thickness of glaze applied. Trial and error is the best way to determine the proper thickness and the best method of applying a glaze to reach a desired final appearance. Glazes contain all the materials to make glass plus colorants, materials to give it a desired surface finish (matte, glossy etc.) and, if needed, materials to affect other qualities of the finished product. Although the vast majority of glazes are perfectly safe, some glazes can contain materials toxic to humans if ingested - lead and barium being among the most common. Generally, the toxic materials CAN be rendered safe by proper formulation of the glaze and proper firing. To eliminate the danger presented by improper firings or improper formulation of glazes, I have decided that no materials that could possibly be toxic in a finished piece will ever be used in any piece I create that could come in contact with food.

Sample glaze formula: Celadon - a clear glaze with a blue to green color made popular by Chinese potters of the Sung and Ming dynasties.

Feldspar 217g .........a common part of many rocks. Granite is 60% feldspar.
Whiting 62g ............Calcium carbonate. The major constituent of TUMS.
Kaolin 28g ..............a kind of clay. Very white. Very high melting point. Kaopectate is mostly kaolin.
Flint 79g ..................a source of high purity silica (glass) found naturally as pebbles
Bentonite 2g ...........a kind of clay. Small amounts increase the workability of the glaze. Clumping kitty litter is largely bentonite
Iron Oxide 2g ..........The same stuff as ordinary rust. Here used as a colorant. Iron Oxide (FeO2) can be used to produce many shades of brown, the beautiful and famous celadon greens and blues, and some reds.
Tin Oxide 2g ...........a colorant

Some surface treatments do not involve the use of glazes - substances that vitrify at the proper temperature. On many of my pieces, notably the lanterns, much of the clay surface has nothing on it whatsoever. The pieces are waterproof because the clay has vitrified. Different colors are achieved by brushing various metal oxides onto the surface of the clay. The oxides then combine with various chemicals in the clay upon firing forming glass-like substances called silicates. Compounds of silicon and other materials. The result is a colored surface that has no effect on the porosity of the clay.

FIRING: This term refers to the process of heating a ceramic object in a kiln to a specified temperature for a specified length of time. The temperature and length of time are determined partly by the materials used, partly by the effect desired and partly by the stage in the process.

In most cases there are two stages. The bisque firing and the glaze firing.

BISQUE FIRING: The purpose of this firing is to remove the water chemically bonded to the clay molecules. This changes the chemical structure of the ceramic objects so that they can no longer revert to a soft moldable form if they come in contact with water. The bisque firing also makes the clay body fairly porous so that it will allow the wet glazes to be adsorbed onto the surface of the object. A bisque firing typically reaches a temperature of between Cone 010 (1634 o F) to Cone 04 (1922 o F) in 8 to 12 hours. Cooling the kiln takes another 8 to 12 hours. Heating and cooling take place slowly to prevent cracking. A ceramic piece will shrink from 8% to 15% during the production process. The greatest amount of shirnkage occurs while the object is drying just after being made. A certain amount of shrinkage occurs in the bisque firing and in the final glaze firing. Total shrinkage depends on the type of clay used. Porcelains and other very fine clays shrink the greatest amount while earthenware and similar bodies shrink less.

GLAZE FIRING: The purpose of this firing is to turn the glaze materials which have been put on the surface of the object into a glass-like substance AND to vitrify the underlying clay body. Various clays ‘mature’ or become vitreous (glass-like and impervious to water) at different temperatures. This ranges from very low temperatures (Cone 06 1841 o F) with clays such as earthenware and Terra Cotta to clays that mature at comparatively high temperatures (Cone 10 (2300 o F) for stoneware and porcelain. Different glazes turn glass-like at different temperatures. So, the glaze chosen for the object must mature at a temperature compatible with the clay with which the object was made. Other qualities of the glaze and clay object must also be considered in choosing a glaze including, obviously, the color and texture of the finished piece and, not so obviously, the rate at which the clay object and glaze shrink and expand. Many qualities of the glaze can be altered by changing the formula of the glaze. Trial and error is the best method of arriving at a glaze that is both aesthetically pleasing to the artist and functionally appropriate to the piece.

Because of the extremely high temperatures reached in either the bisque or glaze firings, ceramic pieces are usually oven proof, microwave safe and dishwasher safe. Typically, ovens don't go over 500 oF. The same for dishwashers and microwaves. Care must be taken, however, not to place a ceramic object in an extremely hot oven without first pre-heating it. Also, certain glazes contain large amounts of metals like iron. These can cause arcing problems in some microwave ovens.

KILNS: There are two types of kilns - electric and kilns that burn something to achieve elevated temperatures. Each type of kiln produces different results. Much of the result is based on the type of atmosphere present in the kiln during the firing. An atmosphere in which the percentage of oxygen is about the same as normal air (23%) is called an oxidation atmosphere. An atmosphere where there is no oxygen is called a reduction atmosphere. In an oxidation atmosphere chemical reactions between glaze components and the clay body take place in the presence of oxygen. Certain chemical compounds result and produce specific surface effects and colors. In a reduction atmosphere, reactions occur in the absence of oxygen producing very different surface effects and colors - many times with the same glazes used in oxidation.

CONE: This is a ceramics term for a temperature measuring device and has come to represent a specific temperature when associated wit a number.. It comes from the cone-shaped pieces of clay that melt at different and very precise temperatures that ceramists use to determine the exact temperature of the kiln when an electronic sensing device (pyrometer) is not available. The difference between the melting point of the cones is not consistent. The range between the lower melting cones tends to be greater than the range between the higher melting cones. For instance Cone 015 is 1418 o F and the next cone in the series, Cone 016, is 1463 o F, a difference of 45 degrees. Cone 9 is 2282 o F and the next cone in the series, Cone 10, is 2300 o F, a difference of only 18 degrees.

STUDIO

My studio is at 4636 N. Ravenswood in the Bull Dog Lock Company Building, (1600 west) between Wilson and Leland on Chicago’s North side.

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