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Published Feb 16, 2009

As ceramic artists, we are all familiar with unhappy accidents. But sometimes we are lucky enough to experience unhappy accident's cousin, the happy accident. When Mary Cay was a student, she became fascinated by the little jewels of glaze that sometimes ended up on the kiln shelves from a pot that was glazed too heavily. She began to wonder if she could intentionally create these little gems. So she started experimenting. This experimentation changed the direction of her work.

In today's post, an excerpt from the Ceramics Monthly archive, Mary shares her process for cultivating kiln jewels to bedazzle her pots. - Jennifer Poellot Harnetty, editor.

Kiln Shelf Preparation

The first step in the process is to apply a wax-resist/alumina hydrate mix to bare mullite kiln shelves. Mix equal parts wax resist and alumina hydrate by volume. Stir well and often. For Limestone Base Glaze, use four parts wax resist to one part alumina hydrate by volume. For Judy Cornell’s Moon Celadon glaze, use two parts wax resist to one part alumina hydrate by volume.


“Three Vessels,” 8 in. (20 cm) in height, porcelain, with Bone Ash and Sky Blue glazes, and Copper Sulfate and Sky Blue Glaze Kiln Jewels, 2005, by Mary Cay, Conifer, Colorado.

After washing the kiln shelf with hot water, quickly apply the wax-resist/alumina-hydrate mix to the shelf with a sponge brush (purchased from any hardware store). Allow drying just to the point at which the wax is no longer tacky and then apply a second coat. For jewels larger than ½ inch in diameter or for the Celadon kiln jewels, apply a third coat. Note: If the wax dries too much, it will repel the next layer of kiln wash. To remedy this, apply hairspray that contains alcohol in even, sweeping coats to soften the wax.


Applying Kiln Wash

Mix the wash to the consistency of heavy whipping cream and apply at least two coats to kiln shelf that has been prepared with the wax-resist/alumina-hydrate mix above. For larger (more than ½ inch diameter) kiln jewels, apply additional coats. To make a smooth surface, spray the kiln wash with water from a spray bottle and allow to dry between coats.

Glaze Preparation

After mixing batches of the glazes, fill several plastic containers and allow them to sit uncovered overnight. The next day, decant all the water that is sitting on top and remix the glazes with a fork. Allow them to sit for another two or three days and decant again. The glazes should then be a very thick paste. Humidity clearly effects the decantation process. In Colorado, a semi-arid state, this process can be completed in three days.

For Judy Cornell’s Moon Celadon, add 1 teaspoon of sodium silicate at a time, and remix to deflocculate the glaze just enough to hold a hemispherical shape as it is extruded from a syringe. For every 24 ounces of decanted glaze, 2 tablespoons of sodium silicate are usually added. For the Limestone Glaze, no sodium silicate is necessary.

“Planter and Tray with Pouring Vessel,” 12 in. (30 cm) in height, porcelain, with Bone Ash Glaze and Sky Blue Glaze Kiln Jewels, 2005.

Glaze Application

Apply the glazes to the prepared kiln shelves through a syringe and fire to Cone 10 in reduction. After firing, the kiln jewels will release from the shelves and can be washed off. If necessary, the bottom can be sanded with a drywall screen.

Post Firing

Kiln jewels can be refired onto ceramics using Cone 017, 05, or 04 glazes as an adhesive, or attached with epoxy in a cold surface treatment.

**First published in 2006.

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Topics: Functional Pottery

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