Re: WoDo White Matte

That glaze is too low in silica, even for a cone 6 white glaze. 
The ratio of alumina and silica is only 4.33 which should be very matt, but
because it's too low in silica, it winds up being a waxy surface because of the
deficiency of silica.
Here's a revision of it, bringing it up around the minimum of 2.5 moles of
silica for cone 6. This will also greatly lower the expansion of the glaze
which will lessen the possibility of badly crazing. The original has an
expansion rate of  8.54 and this has an expansion rate of 7.47.
The ratio of silica/alumina on the revised version is 6.61 which would make
this a nice, smooth matt.

Perry  C 6  Matt 

Nepheline Syenite       39.8
dolomite                20.3
Wollastonite      4.9
OM #4 Ball Clay 16.3
Silica                18.7


If you want it more satiny, you can add 11 more grams of silica which will
bring the ratio up to around 8 which will give a more satin finish. It will
also help the expansion-- lowering it to 7.03.
You might want to do a test of each, and then wet mix equal amount of each of
them to get a third variation.
Note, that when you add high amounts of iron, you risk running unless you up
the alumina and silica. Iron is a very active flux and you have to compensate
for that.


Regards,
June
http://www.angelfire.com/art2/shambhalapottery/