View Larger Image As a participant in the Glaze Forward project, you'll receive tiles of all the glazes (such as this Fake Ash test tile fired to Cone 6) for you to examine and then forward on to the next name on the list.

August 29, 2007

Analyzing Reduction-Fired Glazes at Cone 6

by Diana Pancioli | Read Comments (0)

In Monday’s edition of Ceramic Arts Daily, you read about the “Glaze Forward,” a project that was developed to promote reduction-fired glazes at Cone 6. The project works somewhat like library loan; for a small fee, you’ll receive test tiles along with a booklet of glaze recipes and analyses. You can keep and study the tiles for one week and then forward them on to the next name on the list. As you’ll see in part two of the “Glaze Forward” story, which follows, the glaze palette covers some traditional categories, as well as standard additions to any color palette.

Analyzing Reduction-Fired Glazes at Cone 6
By Diana Pancioli
It is intentional that the chemical bases of the glazes vary—some are high alumina matts, others are high calcium, and so on. Each offers its own advantages, particular surface and color response. Some of these recipes derive from Cone 10 favorites that have been altered to mature at Cone 6 and adjusted to fit a Cone 6 body. Some are not stable, because certain colors and surfaces cannot be achieved without ignoring the limits of stability. High alumina matts, for example, are often not good candidates for wet interiors or utensil use as they show scratch marks.

I have provided strontium substitutes for barium and have added comments about the results of the substitutions on the individual glaze analysis pages. Those glazes containing substances considered toxic have been leach tested by Alfred Analytical Labs. The results are given on the individual glaze analysis pages so that artists may know the precise levels of leaching and can make application decisions accordingly.

The Glaze Forward palette covers traditional categories such as celadon, temmoku, chun/jun and iron saturate, along with some standard additions to any color palette—satin white and transparent. The selections also include colored glazes in matt, satin and gloss, and surface effects such as ash (rivulet).

The clay body used to make the Glaze Forward tiles is similar to Laguna’s B-Mix; it is a white stoneware from Rovin Ceramic Supply called “You Betcha.” This body shrinks approximately 13% and the glazes are corrected to fit a body with that shrinkage rate. I applied a stoneware body slip to the back of each tile to try to give an impression of the glaze over an iron body. I have tested many of these glazes on porcelain as well as stoneware. Some are better on porcelain, some worse; for example I prefer fake ash and green gloss on porcelain—the colors are brighter, but satin celadon and cold yellow appear washed out on porcelain.

On some of the tiles I attempt to show the results of single and double applications of glaze to enhance any potential color shifts. Most of these glazes look best at thin and medium applications.

Where the raw body color shows on the tiles you will notice that the amount of reduction has differed, either from firing to firing, or from different locations in the kiln. The glazes are nevertheless reduced, despite the varying degrees of body reduction.

About the Author
Diana Pancioli is professor of ceramics at Eastern Michigan University in Ypsilanti, Michigan. She conducted this research using their facilities, with the help of her colleague Yiu Keung Lee.

For More Information
You can sign-up to participate in Glaze Forward by completing the form on Diana’s website located at www.glazeforward.com. You’ll be sent a booklet that includes 22 recipes for Cone 6 reduction glazes, their unity molecular formulas, leach test results, and comments. Tiles of all the glazes will be shipped to you later for your examination, on loan, for one week, after which you will forward the tiles to the next name on the list. According to the Diana, the money earned from this not-for-profit project will be used first to recoup the cost of leach testing and preliminary shipping, with the remainder being donated to K-12 ceramic programs.