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substitutes/replacements for colemanite/gerstley borate

updated thu 7 aug 03


Dupre Mr Marcy M on wed 6 aug 03

"And the beat goes on... Drums keep pounding rhythm in my brain..."


In the beginning, there was Colemanite. And it was Good. Colemanite made
delightful glazes, because of various impurities and boron-rich Ulexite.
And the potters saw it. And they used it and it was good.

In the fullness of Time, Colemanite passed on to the great Shard Pit behind
the Barn, and was no more. And there was Gerstley Borate. With great fear
and trepidation, the potters approached this stranger to their midst.

And they touched it, and they tested it, and they tried it. And it was
good. Almost as good as Colemanite. And the potters made glaze after glaze
with Gerstley Borate. Yea, filled many glaze books they did.

They made red glazes, they made green glazes, they made blue glazes. Oh,
how they made blue glazes! And Gerstley made the glazes shine. And
Gerstley made the colors float. And Gerstley made the colors run and
variegate. And the potters saw that it was good.

Then came the dark days of the Closing of the Mines. Dark shadows filled
the skies, and caused a deep trembling in the potters and they were afraid.
Gerstley Borate began to disappear. Some potters gathered unto themselves
the Last of the Bags of Great Gerstley, and buried their hoards to protect
them for the future when there was NO GERSTLEY.

And they wailed, and they cried aloud, and they beat their breasts with
hakeme brushes, and they lamented, "Oh, woe! Oh, woe! However shall we
make our glazes without the Great Gerstley? Oh, Great Suppliers, deliver
(to) us!"

And Hammil and Gillespie heard their pleas. And Ferro heard their pleas.
And DigitalFire heard their pleas. Many were the pleas, and many were the
answers to those pleas.

And the potters saw the answers. And they approached these new strangers,
again with fear and trembling. Many had their triple-beams at the ready,
many had their calculators, many had their particulate filter masks. They
had software--Insight, Matrix, GlazeClac, GlazeChem... Armed with knowledge
were they, and they cried aloud, "How will this change my glaze?" Loath
were they to try the new. But in desperation, try they did.

And lo, it was good. And they rejoiced. And made pots again.


The preceding parable of Replacement and Substitution has been brought to
you by the International Committee for Glaze Material Substitution Sanity
(ICGMSS), a sub-committee of the World-Wide Professional Potters Association
(WWPPA). <>


Personally, I use Gillespie borate as a 1:1 substitute for Gerstley. In one
instance, I have added a small amount of borax to boost the boron content,
but that is an anomaly. In my raku glazes, Gillespie works just fine. Same
for all my cone 6 glazes. Sometimes, I come across a recipe calling for
Frit 3134. I'll try both 3134 in one test, and Gillespie in another test.
Both work very well for me. YMMV.

I have not tried Laguna borate, or Boraq, and cannot speak to those
materials. The only advice I can give is


Have fun,

in soggy Springfield, VA