Paulette Carr on sun 25 jan 04
Nana,
I have only attempted to alter one glaze from ^6 to ^9, and am in the process
of testing it. Specifically, it is the Hesselberth and Roy's Ca Semimatte
Base 1, without colorant, from their book.
As a first approximation, I removed the boron containing frit, replacing it
with G-200 feldspar, increased the amount of Al2O3 and SiO2, keeping the Si:Al
ratio the same, and the expansion the same. At ^9 I do not need B2O3 to help
melt the SiO2 and Al2O3.
I know that the COE (expansion number) is not really meaningful when you are
dealing with a matte/semimatte glaze, but I wanted to keep it the same just as
a starting point. As you might have deduced, I am using a glaze calculation
program to work through the numbers. There is no guarantee that this
alteration will produce a glaze that looks the one at ^6.
In fact, when adjusting a glaze it might have been wise to just make one
change at a time and test it. That way you will know what is working and how much
it needs to be adjusted. For instance, you might find that just removing the
boron is sufficient -- or just raising the alumina and silica. In this case,
I was impatient and just wanted to see what I could do.
Until I fire again (hopefully next week), I will have no results. If you are
interested, I will post a recipe (mine, only) and description of the results,
at that time. I expect to be working on this for some time, unless I get
really lucky.
I hope that this is not too confusing, and will be helpful to you. Good luck!
My best,
Paulette Carr
St. Louis, MO
Nana Underhill wrote:
>>Is there a general rule of thumb for bringing a ^6 glaze recipe to something
that works well at ^8? Is it just a matter, generally of giving it a higher
melting point, or are there other things to consider as well? <<
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