What are Stoneware glazes?

The term stoneware refers to pottery fired to high temperatures, about 2200 degrees Fahrenheit or higher. I fire to cone 6 (2232 degrees F) or higher in electric, gas, and wood kilns.

What are Oxidation Glazes?

Oxidation glazed ware is fired to stoneware temperatures in an atmosphere of abundant oxygen, as opposed to reduction glazes in which the oxygen supply is reduced in the kiln during the firing. Oxidation glazes are generally fired in an electric kiln, which is relatively new technology -  so many potters think oxidation glazes have less character than reduction glazes simply because reduction glazes have had a head start of thousands of years. In fact oxidation glazes are typically brighter and more uniform in color than reduction glazes, because there is no flame swirling around the pots in the kiln.

However, I have been working primarily with oxidation glazes for fifteen years, and I have developed a palette of dozens of colors. My approach to working with them involves pouring and layering several glazes, often using wax resist to mask out portions of the first glaze I applied. This causes the various glazes to mingle to form rich, varied and often unexpected colors and patterns as the glazes flow together.

What are Reduction Glazes?

Reduction glazed ware is fired to stoneware temperature in a gas kiln. Fuel-burning kilns have been used for thousands of years and all of the beautiful classic glazes were developed in kilns fired with wood, coal or gas. In a fuel-burning kiln the fire steals oxygen from the glaze, influencing the fired color. A glaze containing copper carbonate will be green in oxidation and red in reduction; a glaze containing iron oxide may be beige or brown in oxidation but green or black in reduction. Famous classic reduction glazes include Copper Red (Oxblood); Tenmoku, Shino, and Celadon. Often you can see a pattern of varying color on the pot, revealing the path of the flames through the kiln. In this way the potter collaborates with the kiln to produce a unique work of  art. While I may combine glazes in reduction firing, I also try to take advantage of the natural variation of color that a gas kiln can produce in a single glaze.

What is wood-firing?

Wood-firing is exciting and entirely impractical as a production technique for a modern potter. Firing with wood means tending the kiln for many hours, stoking until the temperature inside the kiln reaches the desired endpoint, usually between 2200 and 2400 degrees Fahrenheit.  It means laying in an adequate stock of wood for a firing, for some kilns a cord or more of wood, and splitting all of that wood to a usable size. Usually a wood-fired kiln requires a crew of several people to prepare wood, load and fire the kiln.

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    So why do potters want to fire with wood? Unlike other fuels, wood creates ashes which blow through the kiln and land on the pots, creating a natural glaze. Even where no ashes collect, bare clay can pick up “flashing” where the flame passes. Often wood-fired pots are only partially glazed before firing, so these natural effects of ash-glazing and flashing can enhance the bare clay.

    At the Washington Heights Art Center we have a small wood kiln, which I built with my students in order to test glazes for the gas kiln which is now installed and being used. This wood kiln is so small it can only fit about 20 to 30 pots, and it only takes three or four hours to fire. It still takes three or four people to fire it, one to split wood into very small sticks, one to stoke the kiln, and one to open the firebox door for the stoker. As a kiln it is almost like a toy, but even so some beautiful pots come out of it!

What are Crystalline Glazes?

Crystalline glazes are exacting, frustrating, and exciting to work with. These glazes must “soak” for hours once they reach their melting temperature in the kiln, so particles of silica can migrate through the molten glaze and form crystals, much the way sugar forms crystals around a string suspended in sugar water. However, while the glaze is molten and forming crystals it is also busy running down the side of the pot, threatening to stick the pot permanently to the kiln shelf. The usual approach to working with crystalline glazes is to glue the pot to a pedestal inside a bowl, in order to catch the running glaze, then chisel the pot off the pedestal after the firing. Though I sometimes use crystalline glazes in this way, in other pieces, I pair the crystalline glazes with semi-matte non-crystalline glazes, and hope that the glaze stops running in time. Success relies on getting the glaze formula, application, firing time and soaking temperatures all correct.