"DKat" wrote in message
...
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.