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URL: Floating Blue - Substituting Gerstley Borate
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https://insight-live.com/insight/share.php?z=oLZXQTy9TR
The original floating blue recipe shown side-by-side with variations made using frits instead of Gerstley Borate (and titanium and iron instead of rutile).
Related Information
Titanium instead of rutile for floating blue
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Rutile blue glazes are actually titanium blues (because rutile mineral is an impure source of TiO2 and Fe2O3). The iron and titanium in the rutile react to form the floating blue effect. The GA6-C recipe has always relied on a 4% rutile addition. Its GA6-A base recipe contains significant iron (because of the 80% Alberta Slip), so could titanium oxide deliver the same floating blue effect? Yes. These mugs are M390 clay. The top left one is the standard GA6-C (with rutile) fired using the C6DHSC firing schedule (the bottom left normal cool produces little color). But the ones on the right switch the 4% rutile for titanium dioxide (the L4655 recipe). The top right was fired using the C6DHSC slow cool schedule, the bottom right was the PLC6DS schedule. The takeaway: Titanium is a much more consistent and reliable material than rutile. An excellent blue color is produced even without a slow cool (lower right). A lower percentage of titanium is also an option.
Three rutile blue glazes at cone 6
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These are GA6-C Alberta Slip floating blue (left), AMACO Potter's Choice PC-20 Blue Rutile (center), GR6-M Ravenscrag floating blue (right). The clay is M390. The firing is cone 6, the schedule is C6DHSC (drop-and-hold, slow cool). All of these recipes are descendants and improvements of the 50-year-old original G2826R floating blue. The inside glaze on these mugs is GA6-B. The two on the left develop the blue color because of the slow cool, the one on the right works on fast-cool because it contains cobalt (although it will fire somewhat more mottled). Remember, these work best on dark-burning bodies.
Links
| Typecodes |
Gerstley Borate Glaze Calculation examples
Examples of how we use glaze calculations (in an Insight-Live.com account) to replace Gerstley Borate with other materials, especially frits, in various glaze recipes. In doing so we take the opportunity to improve the recipe in other ways (e.g. reduce thermal expansion, improve slurry properties, reduce bubbling and crawling). |
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| Glossary |
Rutile Glaze
A type of ceramic glaze in which the surface variegates and crystallizes on cooling in the presence of titanium and iron (usually sourced by rutile) |
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