M Richens on fri 18 apr 97
In article <970414211125_75054.2542_GHJ65-7@CompuServe.COM>, Monona
Rossol <75054.2542@CompuServe.COM> writes
>----------------------------Original message----------------------------
>
>
>GAVIN WROTE:
>
>> It's interesting that you can start out with four reasonably insoluble
>> materials, plus one somewhat soluble one, and end up with something that
>> literally comes apart in weak acid. I wonder what is in that stain?
>> There's a lesson or two in this. <
>
>
>I THINK I'VE DIED AND GONE TO HEAVEN.
>
>This is what I've been talking about until I have alienated half the world.
>From what I've seen, the solubility of glaze ingredients before firing is
>irrelevant to the solubility of the finished glaze. And the heat stability
>and acid resistance of a stain has no relationship to its resistance to acid
>in the final glaze.
>
>
>When we fire the glaze ingredients together, we create a whole new entity
>whose properties are unique and individual. Until we have a lot more test
>results on glazes, we don't have a shot at even making educated guesses
>about which glazes are safe.
>
>
>Monona Rossol, industrial hygienist
>Arts, Crafts and Theater Safety
>181 Thompson St., #23
>New York, NY 10012-2586 212/777-0062
>
>http://www.caseweb.com/acts/
Hi Monona,
I agree. That is _THE_ point isn't it. You have to treat it as a system.
BODY-GLAZE-THERMAL_HISTORY.
If you get one badly wrong it doesn't work. If you get one slightly
wrong it may be unstable. There are stable lead glazes, barium glazes,
etc... But there are also many formulations that fall off the edge. The
regions of glass forming can fairly limited but they tend to drift
depending on what you do with regard to the elements you use.
I've known a formulation with Na and K in it that produced good glass.
Swap one for the other 1:1 stepwise towards the K end and the glass gets
a little stiffer and less prone to flow . Go the other way and it became
more fluid until it had nearly all Gp1 alkali as Na and it devitified..
nasty finish. And all I was changing was one for the other.
It's probably worth firing a small tile of the same stuff along-side
your item/masterpiece/workday-pot and test that with drops of common
substances (vinegar, lime juice, Coke) It may weed out the wrong-uns.
Unlike the big companies who can sacrifice articles to destructive
testing.
Max
--
Max Richens max@richens.demon.co.uk +44 (0) 1925756241
Enamel Consultant - Ceramist - Analyst programmer
Software for Batch Formulation and Millroom control.
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