Glaze Stability
Scroll down or click here to find tested glaze recipes
More and more potters (myself included) are wanting to be sure the glazes they put on their functional work are stable so that leaching of any metal oxides they may use will be minimal. This is a controversial area with some saying that there is no need to be concerned except when using the most toxic of glaze ingredients like lead and cadmium. Others want their glazes to be as stable as possible regardless of whether or not there may be any problems caused by glazes that leach. If you are interested in this subject, please read my more detailed perspective.
One of the questions I addressed in doing this work is whether or not traditional limit formulas would predict glaze stability. In a word, there is no evidence in the literature that they will. Limit formulas were derived to define areas of "good glass" without regard to chemical or physical glaze stability. For more information read the paper I wrote documenting my literature search on this subject. Also feel free to download the article Ron Roy and I wrote for the September 2000 issue of Ceramics Monthly titled Making Stable Glazes for Functional Stoneware and Porcelain. And, of course, there is lots more information on this subject in our book, Mastering Cone 6 Glazes.
Brandywine Science Center offers glaze leach testing for potters at a very reasonable cost. The test done is the one described by EPA Test Method 0200.7 and involves a 24 hour leach with room temperature 4% glacial acetic acid (about 80% of the acidity of vinegar). If you want to have your glazes tested, instructions for doing this are readily available. I have had a number of my own glazes tested and am collecting glaze recipes and test results from others who have agreed for me to publish them. From these data plus research I have done myself, we have learned a lot about how to make stable and attractive functional glazes. Still, this must be considered to be a "work in progress" and I invite you to check back frequently to see the latest results.
Please note: The displays of the individual glaze recipes and unity formulas are screen shots from GlazeMaster™ (glaze calculation and database software). For more information on GlazeMaster and free trial downloads, click here.
Most of these recipes can be downloaded in a format that can be readily imported into GlazeMaster. Click on the link on the appropriate page, locate the downloaded file on your hard drive, unzip if necessary, and import into GlazeMaster following the instructions in the User's Guide.
Lastly, note that I have not used most of these glazes myself. I am simply accumulating, in one place, a lot of test work that has been done by many potters around the world.
Potter's Pallette Alkaline Green Black Mat Cobalt Blue Cone 10 Glazes
Shaner's Oribe Waxy Black Old Celadon Rob's Green Esther's White Accented with Shaner's Oribe AW Deep Blue Worner Black
Copyright 1999-2008, John Hesselberth. All rights reserved.