Floating Blue Cone 5-6 Original Glaze Recipe

Code: G2587
Modification Date: 2018-03-22 21:55:20

Floating Blue is a classic cone 6 pottery glaze recipe from David Shaner. Because of the high Gerstley Borate content it is troublesome, difficult. But there are alternatives.

Nepheline Syenite47.944.5%
Gerstley Borate27.025.1%
Iron Oxide Red2.01.9%
Cobalt Oxide1.00.9%

Firing Schedule

Rate (F)Temp (F)Hold (Min)Step


This has been used by thousands of potters over the years, it was originally popularized by James Chappell in the book The Potter's Complete Book of Clay and Glazes. It is the common Gerstley Borate/Nepheline/Silica 50:30:20 highly-melt-fluid transparent with added colorants plus the magic ingredient: Rutile. That makes the colors dance as the glass solidifies during cooling. Colored areas appear to "float" in the transparent. Cappell says this effect is "reminiscent of a deep pool of water".

This recipe actually produces a numbered of different mechanisms of variegation:

People also commonly employ methods to increase the variation of surface color (i.e. stippling a second layer, brushing on a wash of another coloring oxide, double dipping, applying a wash of rutile, etc.).

Anyone who has used this glaze will testify to the fact that it is "fickle" (as Chappell notes). The fickle nature is due principally to the fact the Gerstley Borate is partially soluble and it makes the slurry gel. Among the recommendations he makes is: "Don't substitute any other chemicals for those given". Unfortunately, that is exactly what needs to be done to make this recipe more user-friendly. The boron needs to be sourced from another material (e.g. a frit, Ulexite).

Floating blue is a testament to how unique Gerstley Borate is. This recipe depends on the GB to suspend it (since there is only 5% kaolin) and flux it. Common frits contain less boron. People who have tried to substitute frits have found their results lack one or more of the variegation mechanisms. That being said, there are successful versions of the mechanism (which depends on cobalt, iron and rutile) in other base glazes (e.g. Ravenscrag and Alberta Slip versions).

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By Tony Hansen

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