John Britt on Glazes

You might be tempted to read through the glaze recipes in John Britt’s new book, The Complete Guide to Mid-Range Glazes: Glazing & Firing at Cones 4 – 7, and skip the text. Don’t do it. You might think that because you fire at higher or lower temperatures, the book would be of no use to you. Big mistake. The Complete Guide to Mid-Range Glazes is packed with information and belongs on every potter’s bookshelf.

“Iron oxide, “ Britt tells us, “makes up about 7 percent of the top layer of the earth’s crust, and it’s the most common coloring oxide in ceramics. In fact, iron is everywhere on our planet. Technically speaking, all glazes contain some iron.”  Elsewhere in the text he points out, “There are four major forms of iron oxide. These are red iron oxide, magnetic iron, black iron oxide, and yellow iron oxide.” He then goes on to explain the differences between them and how they react in the fire.

Writing of feldspar he tells us that “most feldspars melt at cone 9, the lowest melting feldspar is nepheline syenite, which melts at cone 6.” Each paragrapah is packed with nuggets like these.

Britt also gives an overview of each type of glaze along with its history. In the section on Temmoku he tells us, “During the Song Dynasty (960-1279), the Japanese visited a monastery in a Chinese mountain called Tianmu Shan (Mount Eye of Heaven), where they collected some Jai (oil spot temmoku) tea bowls. The Japanese were inspired to imitate their look. They referred to their highly prized bowls as Tianmu or Temmoku (sometimes spelled Tenmoku.” Later he tells us “Tea dust is a low alumina temmoku glaze that contains magnesium oxide, which is responsible for the yellow-green pyroxene crystals that are of typical of this type.”

Added to this wealth of glaze and materials information, are charts, photos, advice on mixing and applying, and the recipes themselves. Stunning.

Britt devotes an entire chapter to making his argument for firing at cone 6, citing savings in time and money and the reduction of one’s carbon footprint. “For functional ware,” he writes, “cone 6 stoneware is an excellent choice because it’s very durable and vitrified…so it can withstand repeated trips into the dishwasher and microwave. Also, glazes can be made that are stable and don’t leach harmful chemicals.” He goes on to share his ideas on how best to move from cone 10 down to cone 6.

The Complete Guide to Mid-Range Glazes is a must for every potter’s reference library. Thank you John Britt for your extensive research and in depth understanding and your ability to explain what you have learned so clearly.

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