Use Insight-live to substitute materials in a recipe

We will substitute wollastonite for whiting and a frit for Gerstley borate in the G2571A cone 10 matte while maintaining the chemistry of the original recipe.

A. Insight-live

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A two-minute silent video with annotations.

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Recipes	G2571A - Cone 10 Silky Dolomite Matte glaze A cone 10R dolomite matte having a pleasant silky surface, it does not cutlery mark, stain or craze on common bodies
Glossary	Glaze Gelling Glaze slurries can gel if they contain soluble materials that flocculate the suspension. Gelling is a real problem since it requires water additions that increase shrinkage.
Typecodes	Gerstley Borate Substitutes Many development efforts to create Gerstley Borate substitutes took place during the early 2000s (the initial period when the demise of Gerstley Borate appeared imminent). A number of companies, including Laguna Clays itself, produced and sold these for many years. When Laguna secured another stockpile at the mine and began producing the original material again, interest in substitutes gradually waned. However, the sudden dramatic price increase in 2023 appears to have initiated the process again. Gillespie Borate appears to be the only viable and visible substitute now. Thus, the substitutes listed here are mostly no longer made. Other high-boron materials shown are also no longer available. We continue to recommend sourcing B2O3 from frits instead. Please contact us if you have a specific recipe and we can work with you in your Insight-live account to develop a new recipe that both eliminates the GB and improves overall working and firing properties.
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).

Colemanite and what its decrepitation does in glazes

Decrepitation refers to a decomposition accompanied by scaling, delayering, even disintegration of the glaze layer. Moving rightward these glazes have increasing percentages of colemanite. At its worst (far right) the glaze is spattering off the sample and onto the kiln shelf. The others are crawling, first pulling away from the corners (far left) moving toward pulling away on the flat surfaces (center). Gerstley Borate and Ulexite, similar minerals, are far less likely to do this (but they have other serious issues also). A much better solution is to use frits to source the oxide B₂O₃ (easy to do in your account at Insight-live.com). Photos courtesy of Nigel Hicken.

A unfritted tile glaze is boiling and spattering the kiln shelf above

A boiling tile glaze spatters the shelf above

What you are seeing here is strange indeed. On the bottom is a porcelain tile that was glazed using the recipe indicated. Multiple ones of these were stacked into a kiln, each on its own round kiln shelf. During the firing the boiling of the glaze melt was so violent that it splashed upward, coating the undersides of the shelves above them. Yet no glaze was splattered around the tiles themselves! This phenomenon was created and reported by a researcher working on leadless ultra-gloss metallic tile glazes. This recipe is part of a project to create a similar chemistry to previous work done with Fusion Frit FZ-16. Glazes made using that frit do not have this boiling problem and produce surfaces comparable to leaded frits. We speculate that the vigorous melt is a product of the interaction between the high zinc oxide and borax in the recipe.

Original glaze with Gerstley Borate vs. improved version with frit

These pieces are fired at the same temperature. The glaze on the left is a popular recipe found online, Worthington Clear (our code number G2931). The Gerstley Borate in it is "farting" as the glaze is melting (the calculated LOI of the glaze as a whole is 15% mainly from that one material). Unless applied very thinly tons of micro-bubbles appear (this example is fired to cone 03). And strange, it is crazing badly also despite the low calculated thermal expansion. Using my account at insight-live.com I was able to source the B₂O₃ and MgO from a frit (actually two frits) to create the G2931K recipe. Although the thermal expansion calculates higher it is strangely fitting better (albeit not firing as white). As you can see, the new fritted glaze is very glassy and clear (thick or thin).

By Tony Hansen
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