Iron Red Glaze

This cone 6 iron red glaze was created to replace a recipe that used Gerstley Borate. Since Gerstley is no longer available, I used a boron frit to source the boron. The original recipe had an impossible amount of boron from an extremely high Gerstley Borate content. This probably provided the melt fluidity, but there are better ways of making an iron red glaze.

The replacement was made by combining two sources:

1. Derek Au's testing of a cone 10 iron red glaze
2. Chazo Chazim Mehmeti's observations on iron red glazes

From these two information sources, I came up with these chemical guidelines:

• Less than 0.25 molar Al₂O₃ for melt fluidity and crystallization
• Silica-Alumina Ratio between 8.0 and 8.5
• 0.15 molar B₂O₃ to melt at cone 6
• Flux ratio of 0.2 KNaO, 0.6 CaO, 0.2 MgO
• 0.1 molar P₂O₅ for the iron red effect
• 10wt% red iron oxide to saturate the glaze melt

Porcelain	White Stoneware	High Iron Stoneware

This glaze worked first on the first try. That's the power of glaze chemistry, baby! I got lovely iron red colors on porcelain, low iron stoneware, and high iron stoneware. The only difference in color is that the glaze breaks black on high iron stoneware.

The synthetic iron oxide, bone ash, and kaolin all contribute to making the glaze rather thick. Since the glaze should go on thin, err on adding more water. In my case I added 90% additional water. The specific gravity came out to 1.45, but I think it could go lower to 1.40.

Created 2024-07-11. Updated 2024-07-18.

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