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:

• Its chemistry is quite different from GB (see chart below): Although they have created a material with similar melting properties it cannot be ignored that glaze color and surface character are a product of chemistry also. This will mean that some glazes will not work. For example, middle fire fluid iron reds and other reactive glazes that crystallize and flow are the most likely to be troublesome because they depend on a critical chemical balance (some have reported getting browns rather than reds in some recipes). Floating blue is a very popular cone 6 recipe and many report that color is different with LB (although still interesting). A popular metallic special effect glaze of half copper carbonate and half Gerstley Borate runs excessively and fails to develop color using LB. However knowledgeable users may be able to compensate other materials in the recipe to contribute less alumina and silica for example. 
• It does not have the same mineralogy. This results in several problems. Many glazes in which GB was used contained no clay and thus relied totally on significant amounts of GB (50% or more sometimes) for suspension and hardness. GB worked very well for this, often gelling the slurry in a way that made it pleasant to use. Laguna Borate will not work in these glazes unless you add about 6-8 parts by weight of bentonite or hectorite for each 100 parts of LB. However this will significantly alter the chemistry and affect the fired results (since Laguna chose to source the alumina, silica, and magnesia from sources other than clay). You will have to test to find out. Another example of a possible problem is chrome-tin pinks and reds. These are enhanced by easily-available calcium oxide (Gerstley Borate contained limestone). However one LB tester reported getting a dusty rose rather than deep purply-red in a popular and reliable cone 6 glaze known as Cranberry. Laguna chose to undersupply CaO and do it from different mineral sources, this is likely the cause. Also, the opalescence and variegated surfaces were due in part to the mineralogy of GB, some users have commented that these effects are not duplicated with LB.

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:

• They did not use Ulexite or Colemanite to source boron because the price of Laguna Borate could not be as low as it is if they did. That means they almost certainly used Cadycal (see the general substitutes page for more information on Cadycal, Ulexite, Colemanite). Laguna is near the Cadycal manufacturer and likely buys it at quantity prices.
• Cadycal has no sodium so they must have added an inexpensive source, almost certainly a soda feldspar. The high Al2O3 content suggests Nepheline Syenite (it is the highest alumina bearing feldspar). 
• Cadycal has little MgO so they must have added dolomite (they did not use talc because it contains silica and the silica content of Laguna Borate is already too high from the feldspar).
• Even after the addition of dolomite the CaO is still too low so they must have added whiting to supply the remainder (they would not have used wollastonite because it is too expensive and also contains silica).
• There is some question as to whether they used a lower alumina feldspar and supplied some of the alumina and silica using kaolin. This is possible because the material is a little brownish in color in the wet state and exhibits a slight plasticity. However the amount of added clay is likely very low.

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 Version

*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.

Overview

Oxide	Rationalized Gerstley Borate	Laguna Borate	L3127B 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.