WoDo White Matte

Have any of you tried this recipe? Also, does it appear to be food-safe?
Thanks!
Recipe:
49 Neph. Sye.
25 Dolomite
6 Wollastonite
20 Ball Clay

None of the ingredients in this recipe are toxic; but to judge it's safety, one
would need to know what temperature you would be firing and then it would have
to be broken down to make sure it has enough alumina and silica to be a good,
functional glaze. Also, if you intend to use colorants with this glaze, the
colorants and amounts would have to be taken into consideration.

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

Hi June,
Thanks for your speedy reply. I will be firing at ^5 to ^6. Right now I will be
just testing the base recipe so I don't have any colorants percentages worked
out yet. Some suggestions I have come across and would like to try are the
following percentages:
5 tin ox. and 1 cob. carb
5 rutile and 1 cob. carb
5 rutile and 2 cob. ox
10 RIO
8 RIO and 4 rutile
yellow ochre at 10-12

This WoDo Matte is reported to be a waxy white. I would love to hear from
others who may have tried it so I can get various opinions. I'll be trying it
myself soon, one way or the other. My main concern was for any toxicity levels.
I checked before I posted here, but want ed to hear from those more
experienced. This will be my first self mixed glaze and I don't want to screw
up right off the bat.
Thanks so much, Gaye

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/

In article ,
ShantiP1 wrote:

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/

I was curious about this last part. I've been working on throwing for
3 years, and have never gotten into the chemistry of glazes or clay
bodies. Now I'm working with a flameware claybody, with a high iron
content. The glazes that are suitable for this claybody tend to run a
lot. They've been nice looking, but ultimately disappointing. Could
the high iron content of the flameware claybody have anything to do
with the glaze running? Would there be a way to compensate? I've
tried to find glazes suitable for cone 10 flameware, but there aren't
too many recipes out there. Could it just be a matter of thinning the
glazes more than usual, or maybe dampening the bisqueware before
applying the glaze? Anyone have any suggestions?

Thanks.

Deb R.

June,
Thank you for your advice and revised recipe. I printed out your post. I
appreciate you going through all that trouble. I plan to test both. Now, you've
prompted another question...you said the recipe I posted was too low in silica
and that's why it is waxy...I think I would like it waxy. That was part of what
made me interested in the recipe. Do you think it would be foodsafe or, if I
decide to use it, should I stay away from anything to do with food consumption?
Thanks again.
Gaye

(GaSeku) wrote in
:

June,
Thank you for your advice and revised recipe. I printed out your post.
I appreciate you going through all that trouble. I plan to test both.
Now, you've prompted another question...you said the recipe I posted
was too low in silica and that's why it is waxy...I think I would like
it waxy. That was part of what made me interested in the recipe. Do
you think it would be foodsafe or, if I decide to use it, should I
stay away from anything to do with food consumption? Thanks again.
Gaye

Gaye

Your glaze is not foodsafe.

It does not fall into the limits for a food safe glaze. You do not have
enough silica to fully form a glass. To be food safe glazes need to be
hard and shiny. Matt glazes are for decoration.

I have forwarded you a Matrix printout so you can visually see that it
does not conform

John W

When a glaze is low in silica, the low silica keeps the glaze from forming a
glassy structure which would hold coloring oxides in solution. When they aren't
held in solution, then acidic foods, dishwasher soap, etc. can literally pull
the oxides out of the glaze and at least wash the color out of the glaze and at
worst, deposit potentially toxic oxides into the food.
Matt glazes can be perfectly food safe. They just have to be properly
formulated with and the right amounts of materials and alumina and silica for
their temperature range to make a safe, balanced glaze.
As far as flameware goes. It is something I would advise to shy away from, at
least commercially. There have been a lot of law suits over flameware which is
why you rarely see potters making it any more. You are very limited to the
glazes you can use because to make the glazes fit the body, you need very low
expansion glazes.
The iron certainly can be part of the cause of the running, but in a properly
formulated and fired glaze you can have high iron without running. It's all a
matter of balancing the formula and the firing.

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

Excellent explanation June. Thanks! Gaye