View Larger Image “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.

April 4, 2007

Glaze Kiln Jewels: A Glittering Obsession

by Sumi von Dassow, Ceramic Arts Daily | Read Comments (0)

Many artists’ greatest works have been the result of happy accidents leading to entirely new and unforeseen developments. Indeed, the ability to see the opportunity presented by an unexpected result and allow one’s train of thought to be sidetracked onto an interesting and unplanned journey practically defines creativity.

Pottery, perhaps more than any other art form, is particularly subject to accidents, happy or otherwise. The alchemy of the fire and glaze leads to surprises, angst, joy and tears when kilns are opened. One small surprise is the jewel of glaze that occasionally appears on a kiln shelf under a too-heavily-glazed pot—most likely found in studios in which the inexperienced student layers many glazes. The pot that produced the jewel is usually a dud, but few could fail to feel a moment of delight at seeing a perfectly round jewel of glaze. Undoubtedly, many ceramics artists stash these little gifts of the kiln gods away to use some day, some way.

While a student at Metropolitan State College of Denver (MSCD), Mary Cay became enamored with these little jewels and began collecting them during the kiln openings. After the death of Rodger Lang, her mentor at MSCD, she made a piece with all the jewels she had collected and dedicated it to him. Another of her early pieces using these jewels was included in the Emerging Artists feature article in the May 2002 issue of Ceramics Monthly.

Seeing myriad possibilities of working with glaze kiln jewels, she was determined to grow them—or as she quipped “cultivate them rather than mine them.” The trials and errors of this project consumed two years of study, initiated conversations and recommendations from other artists, and eventually resulted in the manufacture of thousands of glaze kiln jewels per kiln firing. The goal was reached, but equally importantly the process led to self-discovery. “Working with porcelain and glazes has taught me to be patient, reflective, and most importantly that timing is everything. Taking on this project led me to use an element of scientific methodology by changing one variable at a time to achieve my goal.”

Spending two years to perfect the manufacture of glaze kiln jewels may seem a risky enterprise with an uncertain payoff, particularly in a soundbite culture craving instant gratification. But consider that artists have consumed entire lifetimes seeking such elusive goals as the refinement of porcelain production in seventeenth- and eighteenth-century Europe; an investment of energy the legacy of which continues to this day. One can do worse than to follow the model of past masters, painstakingly documenting every success and failure, building on knowledge gained from successive firings, and developing an intimate and committed relationship with the work.

In the end, Cay found that the secret to making successful glaze kiln jewels lies first in taking copius notes and then in the proper preparation of the kiln shelf as well as of the glaze mixtures themselves. Different kiln washes are required for different glazes, and while some glazes work better if they are mixed with sodium silicate, other glazes work best when mixed normally, allowing them to settle and then decanting to remove the excess water from the surface. The basic method is to wipe a mullite kiln shelf with warm water to reduce its absorbency, apply a layer of a wax-resist and aluminum-hydrate mixture, and then apply two or more layers of kiln wash. The thickened glaze is then applied onto the damp kiln shelf in several rows of large drops using a syringe. After firing, the jewels are scraped off the shelf, washed and scrubbed on a piece of drywall screen to remove any kiln wash still adhering to the bottom of each jewel. The correct preparation of the kiln shelf reduces the crusting and makes this last step as easy as possible.

Cay’s technological achievement, far from being an end in itself, leads to numerous possibilities. On functional ware, a clear glaze is applied to the bottom of the jewel and after another firing becomes melded to the ware, making it food and dishwasher safe. When the jewels are placed on the bottom of a piece, they elevate the piece off the surface at the same time protecting the surface. On nonfunctional work (both ceramic pieces and mixed-media work) the jewels can be glued with epoxy or embedded in caulk.

For bonsai-inspired planters the jewels rest on top of the soil allowing the water to evaporate less. In installations, jewels have been arranged on gallery walls by first gluing them to carpet brads, drilling 3/16 inch holes in the walls and inserting the brads. Embedding the jewels in greenware and firing results in a finished piece oozing the sparkle peculiar to these gems. Cay’s studio mate, Gail Fraiser, makes large sculptural vessels and has started purchasing jewels as embellishments to her Shino-glazed pots. Undoubtedly many new uses for the glaze kiln jewels remain to be discovered, a prospect which never would have materialized had the diligent investment in the process never been made.

Mary Cay is represented by the Evergreen Gallery (www.theevergreengallery.com) and by McGrath and Braun Art Consultants (www.mcgrathandbraun.com).

Monthly Methods: Farming Kiln Jewels

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.

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.

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.

 

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Recipes

 

Kiln Wash for Limestone Glaze

Calcined Kaolin................................................ 50%

Silica (Flint)..................................................... 50%

..................................................................... 100%

 

Kiln Wash for Judy Cornell’s Moon Celadon

Alumina Hydrate............................................... 60%

Calcined Kaolin................................................ 20%

Kentucky Ball Clay........................................... 20%

..................................................................... 100%

The following recipes were given out during the summer session at New York State College of Ceramics at Alfred in 1998.

 

Judy Cornell’s Moon Celadon

(Cone 10)

 

Whiting ........................................................ 16.2%

Kona F-4 Feldspar ........................................ 50.5%

Silica (Flint) .................................................. 33.3%

.................................................................. 100.0%

Add:

Bentonite ....................................................... 1.0%

Barnard Clay................................................... 5.5%

 

This is a glaze that settles easily, so add 3 tablespoons of Magnesium Sulfate (Epsom’s Salts) to a 10,000-gram batch of glaze.

 

Limestone Glaze

(Cone 10)

 

Whiting ........................................................... 15%

Custer Feldspar................................................ 49%

Kaolin ............................................................. 13%

Silica (Flint)..................................................... 23%

..................................................................... 100%

Add: Bentonite................................................... 2%

 

Stains can be added to this glaze according to the manufacturer’s recommendations. For Yellow Glaze Kiln Jewels, 3% Cerdec yellow stain was added.

 

Carbonates and oxides also have been added to this recipe with success by using various proportions. A strong cobalt glaze was mixed with this glaze to produce the Sky Blue Glaze Kiln Jewel, but cobalt carbonate or oxide also could be used.

 

A wash of copper sulfate can be sprayed or brushed on to create the Copper Sulfate Glaze Kiln Jewels.

 

Bone Ash Glaze

(Cone 10)

 

Bone Ash ......................................................... 5%

Dolomite.......................................................... 30%

Kona F4 Feldspar............................................. 40%

EPK Kaolin ..................................................... 25%

..................................................................... 100%

Add:

Bentonite........................................................... 2%