The writing on the wall is that the University is not going to allow us to use Talc either in our glazes or our clays (how in the world you are supposed to find that out given the mix we have that has come and gone and the recycling done...).
Our best glazes use Talc. What in the world can you do to substitute it especially given that I have used it to keep glazes from crazing and it is the only thing that worked.
Donna
Talc adds magnesium to glazes and is used as a flux in some low fire clay bodies to lower the maturing temperature and extend the firing range. It is primarily used in white hobby and school type modeling clays. I'm not sure what would substitute for it in a clay body, perhaps a frit or other prepared fluxing agent. Or, perhaps dolomite and silica could serve this purpose in a body.
Talc is magnesium silicate and provides both magnesium oxide and silica to a glaze. Magnesium can be gotten fom dolomite which is a calcium, magnesium carbonate or from chemical magnesium carbonate.
If substituting dolomite for talc, up the amount of silica in a recipe and decrease the amout calcium carbonate, whiting, until the same equivalents are in the recipe as before.
If substituting magnesium carbonate up the silica, but don't do anything to the calcium.
If you know how to formulate glazes, this should be trivial. If you don't I would be more than happy to propose an adjuted recipe for you to try.
Just post here or e-mail a favorite talc, glaze recipe and I'll take a stab at modifying it for you to try. It should act in every way the same as the original recipe because all of the elements will be the same, only from different sources.
My e-mail address is montassocatyahoodotcom Please fix the at and dot.
I can formulate glazes. I was hesitant to use Magnesium because I cannot even image the volume I would need for the equivalent. Dolomite does not work in the glazes that iis used because the calcium to magnesium ratio doesn't work. One of the glazes is Randy's Red (ours is Toby's but very similar).
Toby's Red ^6
32 gerstly 30 flint 20 kona f4 14 talc 5 epk 15.15 RIOroughly goes to
32 gerstly 30 flint 20 kona f4 8 magnesium carb 15.15 RIOWhen this gets upped to 10000grams that is 800 grams of Magnesium Carb.... That strikes me as a huge volume but I may be remembering wrong.
If you think this is worth the try, I will mix up a batch. Thanks, Donna
So, what is the University's reason for this? Is the about the talc itself (magnesium silicate), or some impurity? Considering that baby powder is talc, and the way it is applied (through those shaker-top squeeze bottles) puts a lot of it into the air, compared to a potter stirring talc into a glaze, one has to wonder. Or is baby powder now an endangered species as well?
Best regards,
Bob Masta DAQARTA v3.50 Data AcQuisition And Real-Time Analysis
I don't think you can use magnesium carbonate... the glaze will crawl off the pot and out of the studio!
Best regards,
Bob Masta DAQARTA v3.50 Data AcQuisition And Real-Time Analysis
Apparently Ceramic Supplies (NJ) gets its talc from a mine in Connecticut where the talc has been contaminated with asbestos. The University Environmental 'police' confiscated our talc and were going to take our glazes made with talc. They were talked out taking the glazes. I learned this morning that we are going to try to get a replacement talc from Texas...
I keep on swearing I'm not going back into the studio yet I keep finding myself there.
....
Donnna
try baby powder on sale at walmart. read the label, as some baby powder is really corn starch.
It sounds like you have it in hand and can reformulate if necessary but with Texas talc or another source, that may not be necessary.
I was trying to look at the molecular formulas and can't find, in this short time, a proper formula for Gerstly Borate, Some references are giving the formula for Colemanite under Gerstly but they are not the same. Furthemore, I understand the Gerstly mine has closed which means you may have to re-formulate anyway regardless of the talc issue. Thoughts?
I will still play around with formulations as time permits and post them here.
BTW, the above formula just replaces talc with magnesium carbonate but does not adjust the silica or the lime in the Gerstly. The silica and alumina balance is even worse because there is no kaolin. It would probably give very different results.
Talc occurs in association with asbestos. This is why most, if not all, baby powders are corn starch. Adult powders might be more likely to have talc. I'd imagine that any talc source could end up containing asbestos as they went from one end of the mine to the other. And like any sort of contamination, the government can change the allowable parts per million or whatever.
The Canadian government is still trying to mine and sell asbestos as an insulation. It's doing this because there are great quantities of it in Quebec. But it generally* can't be sold in Canada and there are fewer and fewer takers because the stuff is so bad for the lungs.
Elaine
my local water company used to keep spare pipe in the property behind my house. it was asbestos concrete pipe. properly encapsulated, there's nothing wrong with asbestos. of course, the producers have to properly protect their workers, but the end product isn't going to be air dispersed.
regards, charlie cave creek, az
This link may explain why the University is suddenly eradicating talc. It probably popped up on a new hazardous materials list.
This site seems -- well a bit off. For one thing talc is not toxic. It does not poison you. What this article meant to suggest is that it may be carcinogenic Talc is often found near deposits of asbestos and can be contaminated with it. While it may have a physical structure similar to asbestos if it is ground fine enough, it does not. Talc in general is not considered a problem. It is only that talc which we got from a mine in Connecticut that was contaminated with asbestos that is being treated as a problem.
Talc not containing asbestiform fibres is not classifiable as to its carcinogenicity to humans (Group 3).
Talc containing asbestiform fibres is carcinogenic to humans (Group 1).
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