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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.

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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 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).
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.

Colemanite: How decrepitation can disrupt a glaze

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Colemanite can fracture and disintegrate as it releases chemically bound water during heating—a phenomenon called decrepitation. In a glaze coating, this can cause cracking, flaking and even particles being thrown off the ware before the glaze melts. The damaged layer can then crawl as melting proceeds.

These glazes contain increasing percentages of colemanite from left to right. Bare areas become progressively more extensive, culminating in severe disruption on the far-right tile. Gerstley Borate substitutes containing raw colemanite carry the same risk (the higher the percentage the greater the problem). Gerstley Borate itself is a mineral mixture containing colemanite and ulexite; ulexite is much less prone to this fragmentation. A more dependable way to supply B₂O₃ is to reformulate using boron frits. Insight-live.com not only helps do this but also document the testing.

Photos courtesy of Nigel Hicken.

Intumescence: Borax does this during firing

And it is not pretty what can happen in a glaze

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This recipe was an attempt to reproduce the exceptionally glossy surface achieved using Fusion Frit FZ-16. But supplying similar oxides from raw materials produced dramatically different firing behavior - the glaze has spattered onto the kiln shelf above! The raw version contains 35% borax pentahydrate. During heating, this releases chemically bound water and can swell—a process called intumescence, with expanded particles subsequently bursting into dust and flakes. Later, calcium carbonate releases CO2, potentially feeding bubbles into an already developing melt. Early particle ejection and later bubble bursting are both possible contributors to the spattering.

Notice the calculated LOI: 13.9% for the raw recipe versus 1.8% for the fritted one. Frit manufacture has already driven off the water and decomposition gases from the materials incorporated into the frit, combining their oxides into a glass.

These two formulas are not exact matches, but it illustrates a limitation of recipe calculation: matching an oxide formula does not reproduce the way a glaze behaves on its way to becoming glass.

Original glaze with Gerstley Borate

Improved version with frit

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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 clouds of micro-bubbles appear and opacify it (this example is fired to cone 03). And strangely, it is crazing badly 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 and is very glassy and clear (thick or thin).

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