David Lambie on tue 22 may 07
Dear Ron Roy,
I've looked through your book and I like the glazes that you present
but my kiln can only fire to cone 5 currently, because of electrical
considerations. Would the glazes in the book be considered food-safe
at cone 5? If not would the glazes need to be reformulated for cone 5?
Also, where should I start if I wanted to color the high calcium
semimatte a red color (similar to the Raspberry glaze)? I'm new to
glaze chemistry and knowing the exact chemicals to add is a little
difficult since I don't know the chemical makeup of the ingredients.
Thank you for your help,
David
John Hesselberth on tue 22 may 07
Hi David,
The glazes will definitely be less stable at cone 5. For some the
difference would be small enough it would have no practical effect,
e.g. Waterfall Brown and some of the glossy glazes with low levels of
colorant. I would be more worried about the high calcium semimattes,
particularly the one containing copper. The only real way to tell, of
course, is to test the glazes. You can get a good idea of the effect
by doing a vinegar test.
Lowering the maturity temperature 1 cone would probably require
increasing the boron level about 0.05 in the unity formula.
Lastly, I suspect you will have a good deal of difficulty getting a
semimatte Raspberry in a chrome/tin pink. Chrome tin pinks are pretty
fussy on composition and we had to go through a lot of iterations to
get the glossy Raspberry. I've never tried it with one of the high
calcium semimatte bases though, so give it a try and see what happens.
Regards,
John
On May 22, 2007, at 8:32 AM, David Lambie wrote:
> Dear Ron Roy,
> I've looked through your book and I like the glazes that you present
> but my kiln can only fire to cone 5 currently, because of electrical
> considerations. Would the glazes in the book be considered food-safe
> at cone 5? If not would the glazes need to be reformulated for cone 5?
>
> Also, where should I start if I wanted to color the high calcium
> semimatte a red color (similar to the Raspberry glaze)? I'm new to
> glaze chemistry and knowing the exact chemicals to add is a little
> difficult since I don't know the chemical makeup of the ingredients.
>
> Thank you for your help,
> David
John Hesselberth
www.frogpondpottery.com
"Man is a tool-using animal....without tools he is nothing, with
tools he is all" .... Thomas Carlyle
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