Earthenware is a term used in pottery and ceramics to describe the porous, coarse varieties of low-fired clay used to produce the ware. When thinking about clay and all the technicalities associated with glazing and the firing process, remember the simple: dirt, water and fire. Clay is easy. The variables and attributes associated with clay as a medium are endless. Thousands of different techniques using clay additives and glazes have been developed. Earthenware is just a generic term.

Many different mixtures of clay are used for hand building, throwing and molding. Often additives are blended in clay to release color, to make it more malleable, or to make it absorb more or less glaze. Typical red earthenware clays have a high content of iron oxide, which lowers the hardening temperature of the clay and turns the color a dark red. If fired to temperatures above cone 1, it will blister and deform.

When people talk about the “cone” number in ceramics, they are referring to the temperature the kiln is brought to when firing. The term cone comes from a small cone shaped device used to control the temperature in kilns. When the cone burns away at the desired temperature, it turns off the kiln, ceasing the firing process. In electric kilns today, the cone is generally a strip of metal generated to melt when the kiln reaches the set temperature. Cone numbers range from 020 (1175 F) up to 16 (2650 F). The lower the cone, the lower the temperature.

Dry, unfired clay is called green ware. It retains some moisture, is brittle and porous. When you fire clay, you are essentially eliminating the moisture from it. At higher temperatures, the clay becomes dense, strong and less porous, this is stoneware. The highest fired is called porcelain. To give you a rough outline, flowerpots are fired to about cone 014-06 (1500-1850 F), stoneware above cone 6 (2200 F), and porcelain cones 14-16 (2500-2650 F) sometimes higher. These are average temperatures.

Most of what we know as pottery is earthenware which entered the scene about 50,000 years ago, but history has created a number of different glazing and firing techniques that have adopted their own names: cream ware, majolica and lusterware are just a few. These all pertain to the process of firing and cooling, the oxidization or reduction of the piece when fired and the chemical compounds of the glazes and how they are used. The above w/u mentions (twice) crazing, which occurs when a glaze and a body expand or contract at different rates, creating a crackled effect. This is just one of many effects used to change the luster or finish of a glaze.

Earthenware absorbs glaze mixtures well. The body is still porous and the glazes dry quickly. Often clay is fired to earthenware temperature bisque (unglazed), then glazed and fired again to a higher temperature. The bisque creates a durable medium to work with. Green ware sometimes blows up in early firing. A blow up can be caused by a number of different variables; air bubbles, excess moisture in a thick part of the piece or the temperature rising quickly are the most common culprits. The bisque eliminates most of the moisture, contracting the piece, if an air bubble or excess moisture is present, the piece will break as the molecules expand and try to escape.

Breaking a piece in bisque is preferable than having it explode at a higher temperature when glazed, as the piece is ruined and the broken pieces will often adhere to the melting glazes of the other pieces in the kiln.

Earthenware pottery is an interesting medium to work with. Glazes adhere to it well and the firing process uses less energy and time than stoneware or porcelain. Tried techniques can still produce unstable results and the experiment of experience reveals art.