Potters & Sculptors - Making Rock from Mud
Gerstley borate was mined by US Borax up until around 2000, when production ceased. It was an inexpensive source of B2O3 in a fairly insoluble form. The impurities in the mineral lent some rich variegation to glazes and it has been a very common glaze ingredient for many, many years. That said the mineral has been problematic in that the chemical assay varied considerably as it was mined from natural aggregates that were quite inconsistent. Add to that the very high Loss on Ignition, and the partial solubility in water, and gerstley borate is less than ideal for glazes. Nevertherless many potters continue to use Gerstley, and have variously documented their results. The two-penny consensus is to use a more reliable source of borate where the results prove satisfactory, and use gerstley borate where others fail expectations for a more variegated, trailed, glaze matrix.
See Laguna Clay about their stockpile of previously mined G.B.
Laguna says their stockpile is quite consistent in content http://www.lagunaclay.com/support/pdf/Chemical_Composition_of_Gerst...
More at http://www.nmclay.com/Customer_service/Gerstley.htm
A whole lot more at http://digitalfire.com/gerstleyborate/index.html
In a previous life I was a lab tech at US Borax in Boron, California. More soluble forms of borax were mined there, dissolved, and crystallized into 5 and 10 mole "borax". Other processes fused the crystals into anhydrous products. It was awesome to see the fluxing effect of molten borate on hard fire bricks 2 ft thick. The furnaces had to be rebuilt when they got too thin, because the molten borate actively dissolved the interior face of the bricks.
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I've been very impressed with white-burning Bentone EW from China, available from Trinity Ceramic Supply in Dallas TX for about $5 a pound, if you can't find it elsewhere.
http://digitalfire.com/4sight/material/bentone_ew_2932.html
Much less expensive than VeeGum which from my experience has only about 20% of the suspending power of Bentone EW. Digitalfire describes it as a macaloid, but again in my experience has far more suspending ability than macaloid.
Bentone EW is a really important ingredient for reformulating many Gerstley Borate glazes in the Insight-Live database, as Gerstley Borate is often the only suspending clay added. When Gerstely Borate is replaced with a frit, there is often not enough "room in the recipe for more than a few percent Kaolin or Clay. The only other alternative is using soluble Boric Acid or Borax Pentahydrate - far from a good solution.
Using just 0.5% Bentone EW, or less, I can create the suspending ability of 10% Kaolin, Clay or Gerstley Borate.
We have two "complete glaze" ^06 red and yellow cadmium-sulfide frits, CM-940 and CM-941, which fire black if 2% VeeGum is added. I've fortunately been able to suspend these frits using only 0.1% Bentone EW and calcium chloride without much noticeable change in the bright red or bright yellow glazes.
When ever I see a recipe which uses something like 7% bentonite, I know the author was using extremely low-quality bentonite which sells for $0.47 a pound as opposed to the $5 a pound for Bentone EW. So that recipe becomes 2% VeeGum or 0.5% Bentone EW.
There were roughly ten "Colemanite" glaze recipes without photos I deleted in the Insight-Live database. All were identical to other recipes in the database which used Gerstley Borate, with the mere exception that Gerstley Borate had been replace one for one with Colemanite - which hardly qualified as a unique recipe, especially without a photo.
At our studio we mix two parts Laguna Gerstley Borate with one part Mason Stain and six parts water to create our 20 "underglaze" color bottles. The resulting product has more flux than a typical underglaze and sticks better - creating essentially a non-flowing glaze when used alone at cone 6. More often people use these as tints for clear and white glaze - about one part tint to 4 or 8 parts glaze. For the next 20 to 30 years the remaining Gerstley Borate is being sold for less than what it previously sold for.
I had no idea you once worked at US Borax. As you know my only industrial experience was with a electric and gas utility and the oil company Chevron. But both used ceramics.
George:
Before I post a question, let me say I am impressed by the amount of informational and technical resources on this sight. It is apparent that a great deal of time has been spent locating and correlating all of it into one place. I have been experimenting with Calcium Borate for the last year. Have you had the chance to use this product? The general rule of thumb I use in glaze mixing: boron is water soluble, and mineral borate is not.
Tom
Low cost flat lapping disc can be used on you potters wheel if you, drill bat pin holes in it, and provide a trickle of water to cool it. At amazon.com, 120 grit for aggressive material removal. Click the image to purchase
Members have had great things to say about John Britt's new book, Mid-Range Glazes. Click the image to buy from Amazon.com
Purchase Glazes Cone 6 by Michael Bailey, The Potters Book of Glaze Recipes by Emmanuel Cooper, or Making Marks by Robin Hopper, all available at amazon.com. Mastering Cone 6 Glazes by John Hesselberth & Ron Roy is now out of print.
Harbor Freight is a great place to find unbeatable prices for better HVLP spray guns with stainless steel parts and serviceable economy models, as well as detail guns, all tested by our members for spraying glazes, as well as compressors to power the guns. As yet no one has tested and commented on the remarkably inexpensive air brushes at harbor freight.
The critter siphon gun is a spray alternative that is well liked by some of our members, and is available at amazon.
Amazon is also a competitive source for photo light tents for shooting professional quality pictures of your work. They also have the EZ Cube brand favored by several of our members. You might also want to purchase the book Photographing Arts, Crafts and Collectibles . . .
If you are up to creating videos of your work or techniques you might want to invest in a flip video camera
Following are a few scales useful for potters. Ohaus Triple Pro Mechanical Triple Beam Balance, 2610g x 0.1g, with Tare $169.00
And finally a low cost clone of the OHaus. The Adam Equipment TBB2610T Triple Beam Mechanical Balance With Tare Beam $99.62
ebay is a great alternative for many tools and the equipment used in the ceramics studio - kilns, wheels, extruders, slab rollers are often listed there both new and used.
If you just want to spout off, it is best accomplished as a blog posting. If you want to get more guidance and ideas from other members, ask a question as a new discussion topic. In the upper right corner of the lists for both types of posting, you will find an "+Add " button. Clicking it will open an editor where you create your posting. 4/16/2014
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