Boraq Gerstley Borate Substitute Development History

Project Name

Boraq Development Information

Project Codenumber

UnAssigned

Notes

Boraq was developed by Plainsman Clays as a substitute for Gerstley Borate during the early 2000s, the initial period when the demise of Gerstley Borate appeared imminent. Other companies, including Laguna Clays introduced similar products at the time. Later, Laguna Clays began processing a last stockpile of the material they found at the mine and interest in substitutes waned. In 2023 the cycle appears set to repeat. While some of these materials are no longer available, the techniques and test results are enlightening.

While common frits contain boron there is no combination of them that can produce a material that has anywhere close to as much boron as Gerstley Borate (let alone matching the other oddities of its chemistry). For example, compare the chemical formulas of Ferro Frit 3134 and GB. Both have almost no Al2O3 but that is where the similarity ends. GB has 50% more CaO. The frit has 50% more KNaO and more than double the SiO2. Most important, the GB has 50% more B2O3, the key oxide.

Calcium borate frits do exist that are very similar to Getstley Borate (GB), but they are not available. And they have other issues.

The best method to deal with substituting GB is working frits in on a recipe-by-recipe basis (while also assessing other issues like high thermal expansion, lack or excess of clay, running, crawling, etc). The lower the percentage of GB the more practical this approach is. That being said, most people are not going to do that, even if it is the best way. They want a substitute.

These Boraq recipes are examples of some of the tests we made to develop Boraq as a GB substitute. Boraq 1 was sold as a commercial product in the early 2000s. But when Laguna reintroduced GB interest in substitutes waned. As of 2023 all of them appear to be gone!

We wanted Boraq to be plastic like GB, not just high in boron. A number of the other commercial substitutes ignore the plasticity, this is a problem since so many glazes depend on GB for suspending the slurry. The source of the plasticity is hectorite mineral, that is where the MgO in the chemistry comes from. MgO is very important in the way GB fires also, yet some substitutes ignore this.

Boraq 1

Total:100.00

Auto Unity Formula + Analysis

Notes

*This recipe was developed by Plainsman Clays as a substitute for the chemical and physical properties of Gerstley Borate. Boraq 1 was later adjusted to become Boraq 2 and then Boraq 3.

The materials in this recipe are difficult to get in most places. Actually, Cadycal and F-4 Feldspar are no longer manufactured.

We cannot achieve the same boron content using only ulexite (necessitating the use of Cadycal). Boraq 1 was deliberately formulated to have higher boron than Gerstley because, for mineralogical reasons, melting did not kick in well until middle temperatures.

It is possible using only Ulexite to create the chemistry of Boraq 2. Thus we could promote the new product as improved and closer to the chemistry of GB. For people who have used the unmodified Boraq 1 we could recommend that they use pure Ulexite plus a small bentonite addition.

Glaze: Mix the material into G2826Y glaze and apply to small deep bowl made from a light colored body and fire 06. The transparent glaze will pool at the bottom. Unmelted impurities will be evident as specks in the pool or as sharp protrusions from the surface on the vertical sides of the bowl where the glaze is thin.

Bulk density: 23.12 kg. or 50.97 lbs.
It creates a very pleasant slurry consistency but dries slowly.

Pictures

Calculated Loss On Ignition:30.00

LOI

30

XML (to paste into Insight)

<?xml version="1.0"?> <recipes version="1.0" encoding="UTF-8"> <recipe name="Boraq 1" id="67331" key="iyKw8Nf2" date="2023-04-11" codenum="L3127E" loi="" picturebasename=""> <recipelines> <recipeline material="Kona F-4 Feldspar" amount="10.000" tolerance=""/> <recipeline material="Turkish Ulexite" amount="45.000" tolerance=""/> <recipeline material="Cadycal" amount="37.000" tolerance=""/> <recipeline material="Hectalite" amount="8.000" tolerance=""/> </recipelines> </recipe> </recipes>

Born: 2000-06-20, Modified: 2023-04-11 12:28:41

Boraq 2

Total:116.00

Auto Unity Formula + Analysis

Notes

*This recipe was derived from Boraq 1 by simply adding 8 whiting and 8 dolomite. This was done in response to issues with matching the fired properties of Gerstley Borate better in higher temperature glaze recipes.

Three materials in this recipe are no longer available. However, we make this recipe public as an example of how material substitutes can be formulated to emulate the physics and chemistry of others.

The additions drive the B2O3 downward and it would now be possible to supply it using only Ulexite.

Pictures

G2826R Floating Blue melt flow test

Compares Gerstley Borate and Boraq 2
This is a good recipe for comparing Gerstley Borates substitutes.

Boraq 3

Total:116.00

Auto Unity Formula

Notes

*This adjusts the L3127G Boraq 2 recipe by adding 16 whiting to Boraq 1 (rather than 8 whiting and 8 dolomite). The higher MgO in Boraq 2 was affecting some glazes (however it is still the preferred recipe).

Pictures

XML (to paste into Insight)

<?xml version="1.0"?> <recipes version="1.0" encoding="UTF-8"> <recipe name="Boraq 3" id="67446" key="rPMCHkBu" date="2023-04-11" codenum="L3127I" picturebasename=""> <recipelines> <recipeline material="Kona F-4 Feldspar" amount="10.000" tolerance=""/> <recipeline material="Turkish Ulexite" amount="45.000" tolerance=""/> <recipeline material="Cadycal" amount="37.000" tolerance=""/> <recipeline material="Hectalite 200" amount="8.000" tolerance=""/> <recipeline material="Whiting" amount="16.000" tolerance=""/> </recipelines> </recipe> </recipes>

Born: 2000-10-19, Modified: 2023-04-11 09:38:46

Boraq 5 #4 (available materials)

Total:100.00

Auto Unity Formula + Analysis

Notes

*This recipe uses materials that are available in 2023. It is an effort to also do everything we can to be as close a possible to the chemistry of GB. The use of Ulexite as the only boron source, while at first did not seem logical (since natural Gerstley Borate is a Ulexite:Colemanite blend) has proven to work well.

With Boraq 1 we could not achieve the same fluidity with a chemistry that matched GB (so it had to be compromised). However with this recipe a lesser compromise was possible.

There was a question as to whether this will bubble more with the raw dolomite and whiting. However the fired results in glaze recipes look good.

The LOI is about the same as original GB.

Pictures

L3127N Boraq 5 vs Gerstley at cone 04

This match is very very good.

Sample weights 7 g (normally we use 9 g). Both materials still ran off flow tester (fired to cone 04 oxidation). Both appear to have the same amount of glass formation on bottom of flow tester. Both have bubbling (pinholes that actually expose the bare clay surface in some instances) evident on face of flow, with L3127N sample having perhaps slightly more. Both samples had crazing on face of flow tester evident within 24 hours.

L3127N Boraq 5 vs Boraq 2 at cone 04

7 g balls. Both still ran off flow tester. Boraq 2 sample smoothed out more and flowed more on bottom of flow tester. L3127N sample has bubbling (pinholing in some cases that exposes bare clay surface). Both have about the same amount of gloss. L3127N material has filled the socket walls with material, Boraq 2 socket drained before doing so (indicating more early melting activity). Both have crazing evident within 24 hours.

L3127N Boraq 5 vs Boraq1 at cone 04

Flow test sample balls: 3.5 g. Cone 04. Both still melted right off flow tester. Boraq 1 is a little more fluid. Both are crazed, L3127N sample has more bubbling. L3127N has filled walls of socket, indicating earlier melting and bubbling activity activity.

Reference Material

Gerstley Borate

Plastic Calcium Borate

Alternate Names

Colemanite, Calcium Borate, Borocalcite

CAS Number

854267-07-5, 1319-33-1

Volatiles

LOI

29.5%

Formula Weight

140.60

Calculated Thermal Expansion (?)

8.7

Ratios (?)

Si:Al Ratio:25.1:1

SiB:Al Ratio:64.4:1

Alkali Ratio:0.1:0.9

Cost and Cost Units

Can only be set in your own custom materials

Notes

March 2023: Gerstley Borate has just tripled in price. It’s demise is imminent. A search at lagunaclay.com does not return any hits for the term.

No common natural ceramic material in North America comes anywhere close to melting like Gerstley Borate (GB). It begins to melt between 1550F and 1600F and is a clear amber glass by 1750F and ultraclear and glossy by cone 06 (Ulexite melts better but it is not commonly in use in ceramics). It has thus been a staple among potters for many years. 50% can be found in many cone 06-02 glazes and 30% is common in cone 6 glazes. Gerstley Borate is also very plastic and thus suspends and hardens glazes as they dry. In fact, few clays have the plasticity and the ability to retain water that GB has. A GB slurry can take many hours to dewater on a plaster batt, even in a very thick layer. Thus it is common to find Gerstley-Borate-based recipes having no other clay content. Unfortunately many also have clay (e.g. Kaolin, ball clay, bentonite) and lots of GB so they shrink and crack on drying.

GB natural source of boron that was mined in southern California for many years. Mineralogically it is a combination of colemanite, ulexite and high plasticity clay (likely hectorite). The melting behavior of ulexite and colemanite is quite different, the unusual early melting behavior GB exhibits this, it suddenly implodes to a brown opaque melt (because of the earlier fluxing of ulexite) which later turns transparent (when the colemanite joins in).

The mine was closed in 2000 and remaining stocks were to be depleted in 2-3 years. There was alarm across the ceramic community in North America leading up to and after the closure (because Gerstley Borate formed the basis of so many glazes). However in June 2011, the supplier, Lagunaclay.com, announced that there was again a large supply still available (from an unused stockpile). That lasted until 2022 when rumours arose that it would become permanently unavailable.

Prior to, and during the decade of uncertainty about the future of this material, the supplier did not provide updated chemistry information. It was during this time that many companies promoted substitutes. We rationalized it as 24% CaO, 4% MgO, 0.5% K2O, 4% Na2O, 2% Al2O3, 25% B2O3, 14% SiO2, 0.5% Fe2O3 and 26% LOI. In June 2011 we changed the chemistry provided here to the one provided by Laguna on their website (rounded to 1 decimal). This new chemistry has more B2O3 and less CaO (other oxide amounts are fairly similar).

Since GB glazes melt well and are so easy to make, most people have overlooked issues surrounding its use. Glazes with high GB content that host potentially toxic metallic colorants or other materials are often assumed to be non-leachable because they melt well (where as, in fact, they may have an unbalanced chemistry). Gerstley Borate has almost no Al2O3, this is a problem because glazes need it and Al2O3 is normally sourced from clays, especially kaolin. But since GB is so plastic, adding more plastic materials to a glaze causes excessive drying shrinkage (producing cracks and ultimately crawling). One solution is to use calcined kaolin. Another option is to source Al2O3 from feldspar, however to get enough to create a stable glass oversupplies KNaO and causes crazing.

High GB glazes often have alot of micro-bubbles in the fired glass and micro-dimples on the fired glaze surface (most visible in transparents). Slurries also tend to flocculate and gel causing problems with glaze application, drying and adhesion. Because this material melts so well, potters who use it have been willing to endure alot of these issues. One common low to middle fire transparent, for example, has 50% GB and adds 30% kaolin to that, producing a slurry the dries even more slowly, gels quite badly and shrinks considerably as it dries.

The best approach to finding an alternative is the use of glaze chemistry on a glaze-by-glaze basis (to substitute other materials) to use frits to supply the B2O3 or boron (eligible frits also supply CaO and SiO2). This can be done in an account at Insight-live.com. Frits are less volatile, more consistent and reliable and do not flocculate or gel the glaze as Gerstley Borate does. No available frit contains as much B2O3 as does GB, this is some cases it is not possible to source sufficient B2O3. However, in the majority of such cases, the glaze was unbalanced and contained too much boron anyway.

If you need to substitute it in your glazes and need help, just purchase a group account at Insight-live.com and we can work together to get it done. You will end up with a glaze having better slurry properties, fewer bubbles and better fit.

Inventory Movements

Can only be set in your own custom materials