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Laguna Borate

Laguna Clay claims this is almost identical in every glaze they have tried and is less expensive than Gerstley Borate was. At first they offered to help users adapt and you can reach them via an email link at their web site at http://www.lagunaclay.com. Early testers have posted messages on the Internet confirming that Laguna has been helpful when they had trouble getting LB to work. Others have confirmed that its contribution to fired appearance is very similar for some glazes. In our melt flow tests it looks the same (melting to a clear amber free-flowing glass at cone 06). However many users have reported problems with some glazes. You should be aware that there are differences that could be a concern:

The Primary Laguna Borate Advantage

There is no question about it, Laguna Borate is the least expensive option (it is even less expensive then Gerstley Borate was). Thus it appears their philosophy is to make a material readily available at a good price to capture a market share.

The Laguna Borate Recipe

Laguna Borate has the distinction of being the least expensive substitute available. This begs the question: How did they do it? We have come up with a very interesting answer, an answer that really demonstrates the power of ceramic calculations. To guide the calculation of their recipe here is what we know:

Here you can see what the INSIGHT 5.2 recipe window looks like after the calculation was done. The formula is on the lower right. We simply added the materials one-by-one and matched the principal oxide they contributed.
  • The Cadycal supplied the boron
  • The Nepheline supplied the K2O and Na2O (or KNaO combination)
  • The Dolomite supplied the MgO and most of the CaO.
  • The Whiting topped up the CaO shortfall from the Dolomite.

You might think that this all sounds too easy! Well, even if this is not the recipe for Laguna Borate, it has very similar chemistry and physical properties. It would then be a 'substitute for a substitute'. Of all the glazes we have tried, we find the iron reds are the most sensitive. Laguna Borate fires better than Gerstley Borate in the ones we have tried (although it is not nearly as good to apply). Our substitute is virtually identical (having the same shortcoming). Although the formula value for silica does not match it is close. The formula that they use internally for the feldspar, dolomite, and whiting is likely slightly different than ours.

This iron red contains more than 55% Gerstley Borate and has very low silica, no alumina and very high MgO. This is a prime example of a recipe that is almost impossible to mix from any other group of materials. This is because all feldspars contribute alumina, frits have too much silica and not nearly enough boron.

The formula of this glaze is: CaO 0.51, MgO 0.40, Na2O 0.09, Al2O3 0.01, B2O3 0.54, SiO2 1.79, Fe2O3 0.32. Using INSIGHT you can derive a recipe using Gerstley Borate, Laguna Borate or Boraq to supply the above oxides in these proportions.

*The apparent darker color of the sample on the right is due to our scanning, the fired specimens are absolutely identical.

The Laguna Borate

*2826D3 Laguna
Borate Match

The Formula

When first introducing the material Laguna Clay declined to provide chemistry information saying that users could use the chemistry of Gerstley Borate in calculations. However under pressure they did release chemistry information and it turns out that there are significant differences. Also Laguna Borate has a higher formula weight than Gerstley Borate. This normally indicates an adjustment in the amount substituted.  However for now we recommend a gram-for-gram substitution and then an adjustment if melting is inadequate or excessive.


Oxide Rationalized
Laguna Sub

Boraq 1
**Boraq 2
B2O3 29% 27.5% 27.1 34.5% 30.9%
Na2O 4.5 4.0 3.7 3.5 3.1%
CaO 22.0 18.9 17.3 17.8 22.1
MgO 3.5 2.3 2.4 2.2 3.5
K2O 0.25 1.4 1.7 0.6 0.5
Fe2O3 0.2 0.1   0.2 0.2
SrO       0.3 0.2
TiO2   0.1      
Al2O3 1.0 8.1 8.1 2.5 2.3
SiO2 10.0 18.7 21.2 12.5 11.2
LOI 29.0 19.0 18.7 25.0 26.1
Formula Weight 127 171 183 229 185
*Conversion   75% 70% 55% 70%
*Less of this material is needed to substitute for GB. For Laguna Borate, for example, use 75% as much.
**Boraq 2 is Boraq 1 with 8% dolomite and whiting added. It fires almost identical to Laguna or Gerstley Borate in iron red glazes.

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