Ron Roy on sat 26 dec 98
Hi Earl,
I don't think you need to reformulate - just mix some up without the ZnO.
If you want to try it without the Barium - just sub some Strontium carb for
it - three quarters of the amount of BaCO3.
RR
>----------------------------Original message----------------------------
>All of this discussion about zinc has got me thinking, I have this glaze that I
>really like, It's a very dry matt glaze, from the barium most likely. I really
>like it's responses and blushes of clor from oxides, especially copper, and it
>gives great effects with some wood ash sprayed lightly over it, in fact, I
>reall
>don't like the glaze at all unless it has wood ash sprayed over it.
>The glaze is fired to cone 10 in reduction with reduction beginning
>around 1700
>and has 8.8% zinc in it, I think that I had heard/read that zinc
>volitized, but
>didn't make this glaze formula and just assumed that it must be contributing
>SOMETHING? This is the emperical formula for the glaze:
>Na2O 0.14
>K2O 0.09
>CaO 0.31
>ZnO 0.28
>BaO 0.18
>
>Al2O3 0.41
>SiO2 1.86
>
>It would be anybody's guess what the actual formula would be after the ash is
>sprayed on and combined in the melt. I use unwashed barbecue grill
>charcoal ash
>Since connecting to clayart, I've become more conserned about barium, but
>most o
>my peices are more sculptural and less functional. So generally the
>barium cont
>would not be a problem for me. I'm wondering if I need to reformulate
>this Glaz
>Earl Brunner
>
>Ron Roy wrote:
>
>> ----------------------------Original message----------------------------
>> Thanks to Tom for helping on this - Hamer says ZnO is easily reduced - even
>> slight reduction above 925C will eliminate it from the glaze. To answer the
>> question - will it stay in a reduced cone 6 (1200C) glaze - the answer must
>> be no. Besides this it is not an active flux below 1085C. From this it
>> could be surmised that it is not useful as a glaze flux in reduction at any
>> temperature.
>>
>> It makes sense to me that if it is not reduced until the end of a firing
>> that goes above 1085C that it will help the melt and therefore will have
>> some effect - I also have to assume that if reduced at the end at least
>> some of it will be lost and this will have some effect on the durability
>> and the expansion of the glaze.
Ron Roy
93 Pegasus Trail
Scarborough, Ontario
Canada M1G 3N8
Tel: 416-439-2621
Fax: 416-438-7849
Web page: http://digitalfire.com/education/people/ronroy.htm
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