A Hot Glazy Odyssey

Artist Statement

Before this class, I’d never made pottery, so there were many trials and tribulations along the way. However, I learned to be intentional and precise with each step of the process to achieve my desired result and found my niche for making little bowls.

Through my raku and crystalline fired pieces, I explored how different glaze compositions and firing conditions affect the finished ceramic piece, and how these processes can be seen in a natural geologic setting. A combination of cooling rate and redox conditions can completely alter the finish and aesthetic of a ceramic form in replication of processes that occur in the natural world.

Raku is a process that uses the absence of oxygen in the environment to achieve effects like the metallic sheen of the famous “Raku Red” glaze. Raku pieces are fired in a reducing environment, and the dramatic metallic effects on the surface result from copper carbonate, an ingredient found in all raku red glazes, being reduced when it loses oxygen to the gases created in the raku “nest”. This nest is constructed from shredded newspaper that is ignited by the red-hot pottery fresh out of the kiln, and pieces such as the bowl that I created here are immediately suffocated as the nest is covered by dirt and a metal lid, trapping CO, CO2 and H2 that result from combustion of the paper nest. The reduction of copper carbonate turns glazed portions of the bowl a glossy reddish copper to tarnished silver tone, on a gradient dependent on how thick the glaze was. Redox conditions like these are also important in geologic settings, such as in the formation of economically significant sulfide minerals like pyrite and chalcopyrite. Sulfides are created in reducing environments similar to raku conditions with low oxygen fugacity (fO2), which is essentially a measure of oxygen availability in a system. These conditions are what enable precipitation of metals, such as copper, gold, and silver, which are characterized by the same metallic luster seen on the raku piece.

My crystalline-glazed piece represents the importance of temperature change in geologic processes, like mineralization, through the formation of vibrant blue and green crystals. This piece was glazed with a mix of light blue cobalt(II) carbonate glaze and green copper(II) carbonate glaze. Both glazes contain kaolinite, silica and frit 3110 to achieve a distinctive glassy texture upon experiencing a high degree of heat work, and zinc oxide to grow the large, visible crystals. The glaze ingredients allow for heterogeneous nucleation on the existing surface of the pottery while the crystal growth is shown by the rings of cooling periods extending outwards from each crystal. This stepwise cooling rate is the most important factor in the process of crystal growth. Just as crystallization in glazes requires a slow cooling rate, formation of crystals in magmatic systems requires prolonged periods of cooling.