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Getting frustrated Gerstley Borate turning glazes to jelly

I show you why people love/hate this material and how I substituted it for Ulexite in this crazy recipe to make an easier-to-use slurry that fires identically.

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Transcript/Notes

Let me show you what the slurry of Worthington Clear, a 55% Gerstley Borate recipe, is like: A dreadful bucket of jelly!

You'll hear the frustration in my voice about how anyone could use this and about two poor options to endure it:
-Adding water - No good because it will dry even slower.
-Add Darvan - No, it just gels again later.

more..

Using an iPhone and my account at insight-live.com I show you how explore a couple of other options:
-Switching the EPK to calcined kaolin hoping that reducing the total clay content (Gerstley Borate is a clay), will make it gel less. That does not work!
-Switching Gerstley Borate for Ulexite (calculation done off-camera).

For that last option I demonstrate:

How I check the specific gravity.
How I add water to tune the slurry to 1.42 specific gravity.
How I flocculate it with a little vinegar (to be thixotropic), and then enjoy seeing how well it applies to test tiles.
How I use code numbers to organize testing.
How I flip back and forth between my PC and phone when doing the work.

The next day, using my tablet to get into my Insight-live account, we look at the fired GLFL balls, glazed terra cotta tiles and glazed L210 mugs.

Ulexite is difficult to obtain, I used it here just to demonstrate one way option. And even better option is using a frit.

Links

URLs	https://insight-live.com/insight/share.php?z=HzyNzj9ELs Replacing the Gerstley Borate in recipes containing 50% or more of it Many recipes were built on bases employing exceptionally high percentages of Gerstley Borate. At medium temperatures these melt fluid transparents hosted additions of colorants, variegators and opacifiers. At low fire they were used as transparents over underglaze decoration.
Materials	Gerstley Borate Gerstley Borate was a natural source of boron for ceramic glazes. It was plastic and melted clear at 1750F. Now we need to replace it. How?
Materials	Ulexite A natural source of boron, it melts at a very low temperature to a clear glass.
Materials	Gillespie Borate A Gerstley Borate substitute that became available during the early 2000s and is still available in 2023.
Articles	Trafficking in Glaze Recipes The trade is glaze recipes has spawned generations of potters going up blind alleys trying recipes that don't work and living with ones that are much more trouble than they are worth. It is time to leave this behind and take control.
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).

A cure for long-time Gerstley Borate sufferers

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These are various different terra cotta clays fired to cone 04 with a recipe I developed that sources the same chemistry as the popular G2931 Worthington clear (50:30:20 GB:Kaolin:Silica) but from a different set of materials. The key change was that instead of getting the B₂O₃ from Gerstley Borate I sourced it first from Ulexite (G2931B) and then from a mix of frits (G2931K). All pieces were fired with a drop-and-hold firing schedule C03DRH. Fit was good on many terra cottas I tried (pieces even surviving boiling:icewater stressing). Where it did not fit I had thermal expansion adjustability because more than one frit was sourcing the boron. Frits are so much better for sourcing B₂O₃ than Gerstley Borate (the latter is notorious for turning glaze slurries into jelly!). Of course, a little glaze chemistry is needed to figure out how to convert a recipe from Gerstley Borate bondage to frit freedom, but there is lots of information here on how to do that.

Why would a glaze turn into a jelly like this?

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This is one of the things Gerstley Borate commonly does (when its percentage is high enough). It is also highly thixotropic - this can be stirred vigorously to thin it, yet within seconds it turns back to jelly again. This is part of the reason it is often referred to as “ghastly borate”. Side effects of this include high water content, slow drying, excessive shrinkage on drying, cracking and crawling. To attempt a fix, I deflocculated it with Darvan. It was stable enough to dip bisque ware, with difficulty (but pieces dried very slowly). But overnight it has turned back into a gel. What can be done with a mess like this? Start over, with three options:
1. Identify the mechanism to isolate the base recipe and substitute another.
2. Replace the Gerstley Borate with an equivalent that does not do this (Gillespie Borate).
3. Do a little chemistry to source the B₂O₃ from a frit instead (e.g. in an account at insight-live.com).

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.

Click here for case-studies of Insight-Live fixing problems

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You will see examples of replacing unavailable materials (especially frits), fixing various issues (e.g. running, crazing, settling), making them melt more, adjusting matteness, etc. Insight-Live has an extensive help system (the round blue icon on the left) that also deals with fixing real-world problems and understanding glazes and clay bodies.

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).

Gerstley Borate passed on:

It will be missed by many, not by others.

This picture has its own page with more detail, click here to see it.

Near the end, Gerstley Borate first became Costly Borate. The supplier, LagunaClay.com, raised the price to wake us all up to take action in substituting it before supplies ran out. It was a plastic ceramic glaze flux, sourcing boron to melt better than any other common raw material. It had been a foundation material in low and middle temperature pottery glaze recipes for many decades. Potters had a love/hate relationship with it: Enjoying its low melting point but enduring its problems (inconsistency, gelling of the slurry, crawling, micro-bubbles, boron-blue discoloration). Strangely most people used it without knowing what it really was. And few realized how easy it is to replace. Gillespie Borate ended up being the substitute of choice. But it has issues too. The best is to adjust each glaze recipe to source boron from a frit (fixing other issues also).

Please read that last statement carefully. It did not say that there is any frit that can substitute. It said that frits can source boron.

Ferro Frit 3134 is NOT A SUBSTITUTE for Gerstley Borate

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This frit, or any of similar chemistry (e.g. Fusion F-12) IS NOT A 1:1 SUBSTITUTE for Gerstley Borate, their chemistries are too different. That being said, the frit sources lots of B₂O₃, which makes it a candidate to weave into recipes as the source of boron. To show the difference, I have put 100 parts of each in side-by-side recipes in my Insight-live.com account, set the calculation type to non-unity formula and increased the frit until the B₂O₃ in the two match. Notice it takes 118g of the frit to source the same amount of B₂O₃ as 100 GB. Notice also that the frit sources almost triple the amount of Na₂O per weight unit (that is a big deal because it means the recipe containing the Gerstley Borate to be substituted needs an Na₂O-sourcing material that can be reduced to compensate). And the frit sources 3.5 times the SiO₂ (other SiO₂-sourcing materials in the recipe will need to be cut to compensate). And the Gerstley Borate has significant MgO while the frit has none (so an MgO-sourcing material like talc will be needed). Minor tweaks will also be needed to reduce other sources of CaO (since the frit has quite a bit more). The recipe will also need enough flexibility to do the final matching of Al₂O₃ and SiO₂. The GBMF test confirms the difference at 1700F; these 10-gram balls melted down onto the tiles very differently.

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