Fire requires oxygen to burn. When there is a lack of oxygen, the fuel does not burn completely and the kiln atmosphere becomes filled with free carbon. The free carbon atoms will aggressively grab up any oxygen atoms they can find. In fact, carbon atoms are so oxygen-hungry that they are able to break molecular bonds. The carbon literally robs the clay and glaze materials of their oxygen. When the carbon reduces the amount of oxygen in the clay and glaze molecules, the colors and textures of the clays and glazes can change. These changes can sometimes be quite dramatic.
There are many factors to consider when it comes to firing your pottery in a kiln. The term reductionrefers to how much oxygen is in the kiln’s atmosphere while the kiln is firing. An oxidation atmosphere has plenty of oxygen for the fuel to burn. A reduction atmosphere occurs when the amount of available oxygen is reduced.
Missouri Artist On Main exhibits several different techniques of modern American pottery. One way of differentiating between these is to define the work by the type of kiln in which the pottery is fired.
American-style raku differs in a number of ways from traditional Japanese Raku, notably the rich black surface produced by smoking the ware outside the kiln at the end of firing, and the fact that American raku remains porous. Other innovations include the quenching of the red-hot vessel in cold water, the production of brilliant and many-colored copper lustres, the forced crackling of the glaze with smoke penetration, the white line halo or ghost image surrounding a black metallic decoration, and the discovery of a copper slip that sometimes results in an unusual yellow matte surface.
Clay: Let’s Talk Pottery
by resident artist, Clinton Berry
Missouri Artists On Main Gallery 636-724-1260
Pottery usually falls into three main classes—porous-bodied pottery, stoneware, and porcelain. Raw clay is transformed into a porous pottery when it is heated to a temperature of about 500 degrees Celsius. This pottery, unlike sun-dried clay, retains a permanent shape and does not disintegrate in water. Porous bodied pottery is not waterproof, meaning that liquids will leak through the body of the pot. Stoneware is produced by raising the temperature, and porcelain is baked at still greater heat. In these two processes the clay becomes vitrified (able to hold liquid), or glassy, and the strength of the pottery is increased.
Pottery is one of the most enduring materials known to humankind. In most places it is the oldest and most widespread art; primitive peoples the world over have fashioned pots and bowls of baked clay for their daily use. Prehistoric (sometimes Neolithic) remains of pottery, e.g., in Scandinavia, England, France, Italy, Greece, and North and South America, have proved of great importance in archaeology and have often supplied a means of dating and establishing an early chronology. Some of the oldest pottery has been found in Japan and China, dated to at least 16,000 and 20,000 years old respectively. Pottery has also been of value as historical and literary records; ancient Assyrian and Babylonian writings have been inscribed upon clay tablets. Simple geometric patterns in monochrome, polychrome, or incised work are common to pottery of prehistoric and primitive cultures.
Firing of clay objects chemically and physically transforms the clay minerals to produce a hard object from what was plastic material. Up until the object was fired, objects made from clay will rehydrate when subjected to moisture and lose their form. Some low-fired objects, or what has been referred to as ‘soft ware’, may be highly susceptible to weathering and therefore not well preserved in the archaeological record. Earthenware is fired at between 600 and 1000 °C. Some low refractory clay cannot be fired at higher temperatures than this. Open firing was used throughout the world and can be highly efficient for firing ceramics in this range. Formal kilns became prominent parts of ceramic technology in many parts of the world. Kilns are necessary for high-fired ceramics, such as porcelains, which were fired at temperatures of between 1200 and 1400 °C.
American art pottery flourished in the first half of the 20th cent., with works created by a variety of artisans, many of whom were employed by companies such as the Rookwood Pottery and Cincinnati Art Pottery. Much collected in the decades that followed, this art pottery was created in such styles as art nouveau, arts and crafts, and art deco. In addition, many of the major artists of the 20th cent. created exquisite ceramic works. Especially notable are those by Picasso, Matisse, and Miro. In spite of the continuing development of mass-production techniques and synthetic materials, the demand for hand-crafted ware of fine quality has not diminished. A variety of artisans make utilitarian objects as well as works of art using many methods of pottery production.
In the spirit of raku, one must embrace the element of surprise. There can be no fear of losing what was once planned and there must be an urge to grow along with the discovery of the unknown. In the spirit of raku, make no demands, expect nothing, follow no absolute plan, be secure in change. Learn to accept another solution, and prefer to gamble on intuition. American raku is still porous meaning that the object is not vitrified thus not able to hold liquid. American raku is prized for its decorative element rather than function.