Gerstley Borate

Gerstley Borate Update

Gerstley Borate is in stock and not going anywhere!

July 4th 2014           Click here to see prices.

GERSTLEY BORATE (real) A sodium-calcium-borate compound used as a low and mid-range glaze flux. This is a conglomerate mineral made up primarily of Colemanite, Ulexite and Hectorite. Gerstley is a natural borate similar to but not interchangeable with Colemanite on a 1 to 1 basis. 

In early 2000 U.S. Borax shocked the ceramic community by announcing that, for safety and economic reasons, they were ceasing operations at their California Gerstley mine; the source for a unique sodium borate mineral utilized as a basic ingredient in many ceramic glazes for decades. Upon learning this news, Laguna along with other ceramic suppliers and individual ceramists began, in earnest, to research a suitable substitute for gerstley borate. 

This past April, Laguna Clay Co. learned that there remained a limited amount of mined but unprocessed gerstley borate at the now defunct Gerstley mine. Laguna entered into an agreement to purchase all the remaining Gerstley and is milling it to the same specifications as the Gerstley sold over the past 30 years. 

While this supply is limited, based on historic usage Laguna anticipates having an adequate supply for many years. 3000 tons or 6,000,000 pounds as of 6/18/2011! Lots of people were offering synthetic Gerstleys but nobody switched to Laguna borate or suitable substitutes, as they were not as cheap as real Gerstley. 

B2O3    26.80%

CaO    19.40%

SiO2    14.80%

NaO2    3.95%

MgO    3.54%

Al2O3    0.98%

Fe2O3-T    0.425%

K2O    0.399%

P2O5    0.053%

TiO2    0.05%

MnO    0.024%

Trace minerals    0.079%

LOI    29.50%

 Gerstley from Laguna clay

 An older post.... no longer true

As you know Gerstley Borate is no longer available, we have 3 substitutes we have tested and with feedback from our customers we are getting to have a feel for the problem.

Cadycal is a calcium borate , it seems to work best when you were using GB to do something in a glaze. Use 70% of the original amount of GB in your glaze. It does things like break and create a visually uneven color.

Laguna Borate is most useful as an auxiliary melter in a high fire glaze. So when a cone 6 glaze calls for 20% GB substitute Laguna Borate one to one (or less). Major complaint Laguna Boring! It just lays there and makes a boring glaze, great if that is what you want.

Dal Tile's GB substitute from Mexico, we are still waiting for a sample.


Even Older notes on GB......

(from Digitalfire)

Laguna Borate looks like the answer to vanishing Gerstley Borate 

April 14, 2000 

After 3+ months and scores of glaze tests, we've come up with a blended material that looks like the best possible sub for Gerstley Borate. 

You may have heard about Cadycal and other raw materials being tested to take the place of Gerstley, but we found that where those materials work some of the time, Laguna Borate works in virtually every glaze we tested Raku, low and high fire. And guess what, the blended Laguna Borate is actually cheaper than Cadycal! CADYCAL has been discontinued.

The next step is for you to test Laguna Borate in your glazes and your firing conditions. To make this as painless as possible, we re offering the following special as advertised in the May issue of Ceramics Monthly. If you have any questions, drop me a line at 

February 18, 2000

The last two weeks have seen some extraordinary activity in terms of Gerstley sales. The general reaction to the end of Gerstley mining can best be described as panic, in response to which Laguna has been forced to adopt a revised sales approach. 

The "first-come-first-served" plan that Laguna announced five weeks ago is clearly not working. Our hope was that customers would buy enough Gerstley to sustain their production through the time needed to develop and test substitutes for the material. However, it appears that a small number of customers are trying to stockpile as much gerstley as possible for their own economic gain, while others are purchasing a lifetime supply, leaving the majority at risk of not getting material essential for near-term production. 

Given both this "run on the Gerstley bank" and Laguna s declining supply, our singular goal at this point is to be as fair as possible to ALL Laguna customers. Our intention at this point is to provide Laguna customers a quantity of gerstley equal to a six months supply, or one-half the quantity you purchased from us in 1999. It is our hope that Laguna distributors will manage their supplies in a similar manner. Based on the state of our current research, a suitable Gerstley substitute should be available well before the depletion of a six months supply. 

As time goes on, the body of knowledge concerning a Gerstley replacement grows. Laguna has developed a fairly complex formula that is quite close to a chemical match for Gerstley. It has proven a successful substitute in 94% of Laguna s glazes to date; we hope to reach the 98-100% level soon. In addition to Laguna s research, Tony Hansen, with help from Tom Buck, has posted an intelligent treatment of the Gerstley subject on his web site:, and Mary Simmons contributed a helpful post January 15 to the Clayart discussion group. 

We are all unhappy that Gerstley is no longer being mined, but this is a challenge that faces the entire industry. We are confident that the challenge will be met, and soon; but in the meantime let s treat our colleagues with the utmost of respect and fair play. 

We ll continue to keep you posted on this site regarding pertinent information on the Gerstley Borate situation. 

unsigned by someone at Laguna

Gerstley Borate

Mica Red Low fire (018 to 04)

$0.57 Per Pound