Khaimraj Seepersad on mon 3 may 99
John ,
I think I would ask about Li20 , perhaps add it to the same as nickel , lead
etc . Big question as
to where to place B203 and mention that combinations of Sro/ Cr0 are
considered
carcinogenic [ can be seen as Strontium Yellow - Fine Artists ] . Was going
to
suggest Bismuth Oxide in place of Lead Oxide , but I am seeing M. S . D .S
showing it as damaging to organs etc , in Large doses [ how much ?]
Guess you have to keep on your toes .
Zno , someone chime in here please .
From - Khaimraj Seepersad .
-----Original Message-----
From: John Hesselberth
To: CLAYART@LSV.UKY.EDU
Date: 02 May 1999 20:19
Subject: Re: Glaze Development Conundrum
----------------------------Original message----------------------------
David & Diane Chen wrote:
>----------------------------Original message----------------------------
>Maybe if I were a bit further along in glazes I wouldn't need to ask this
>question. However, isn't there a way to determine if something is going
>to be a
>problem before you work out all the problems, decide to love the glaze?
Then
>you send it to this man at Alfred and the recipe to John H, and ta da, it's
a
>horribly poisonous or even mildly unsatisfactory glaze. I know I can read
>about
>how hazardous each ingredient is but then there is the issue of how it
reacts
>with the other things in the glaze. And to make matters even more
confusing,
>this morning in the posts, I read that barium under 7% might be okay. Yes,
I
>could avoid it completely, and am really just using barium for illustrative
>purposes, but IS there a way to find out prior to spending so much time in
>the
>development phase?
>
>Diane
>Massachusetts
Hi Diane,
No, sorry, but with our current state of knowledge there is no simple way
to assure that the glazes you formulate will be durable without testing
them. We are all struggling to learn how to do this. You can increase
the odds they will be durable by staying within published limit formulas,
but you still have to test. I have seen durable glazes outside of limits
and non-durable glazes inside of limits. Unfortunately most of the
serious research on glazes stopped about 50 (or so) years ago and
leaching of lead and crazing were the only durability issues studied with
any thoroughness. The only other way I know of is to stay completely
away from questionable materials and even then you should test for
durability in use.
To increase your odds to the maximum I would 1) stay within limits, 2)
stay away from lead, cadmium, antimony, barium, chrome, nickel, uranium,
vanadium and copper (have I missed any?? what about zinc??) 3) use only
low levels of cobalt and manganese (say less than 2%), 4) use at least
three or four fluxes from the list of K, Na, Ca, Mg, Li and Sr, 5) learn
to like tans, oranges, browns (from iron) or blacks (from iron plus
cobalt) or blues (from cobalt) or whites (from zirconium, tin or
titanium). And then still test. I probably have missed a couple things
here, but I hope someone on the list will chime in to complete it if I
have.
The above might give you a pretty boring set of glazes. On the other
hand, depending on your needs and your style of pottery this might be
just great. Maybe we should have a Clayart contest to see who can
formulate the most attractive glazes from the above guidelines. In any
case this would be a pretty good set of guidelines to follow for a person
who is just starting in glaze formulation. Then as you learn some of the
chemistry and the safety issues you could gradually expand to using other
materials. On the "stay away from" list above, the only one I use is
copper and I work hard to keep it from leaching at high levels. I
probably would use chrome and nickel if I had a need. The others, I just
wouldn't use or don't see why I would want to.
I'd be interested in other's thoughts on the above guidelines to yield a
"high probability of being safe and durable" glaze.
John Hesselberth
Frog Pond Pottery
P.O. Box 88
Pocopson, PA 19366 USA
EMail: john@frogpondpottery.com web site: http://www.frogpondpottery.com
"It is time for potters to claim their proper field. Pottery in its pure
form relies neither on sculptural additions nor on pictorial decorations.
but on the counterpoint of form, design, colour, texture and the quality
of the material, all directed to a function." Michael Cardew in "Pioneer
Pottery"
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