Barbara Long on fri 5 mar 99
A friend has asked that I address this talented group for some technical
advise.She is in the process of moving to a new house/studio and has
already stored her glaze chemicals at the new place.Since then she has
recently mixed up new batches of glazes for her raku work using the same
old bags of chemicals that have been stored in the new studio.The actual
mixing used the water from the original studio,and no new bags of
chemicals.The glazes using copper carb came out with "brown spots" and
the glazes using frits are also flawed.She suspects that the chemicals,
particularly the copper carb,the frits, maybe the gherstly borate have
somehow absorbed water (though they do not feel damp) or they have
become "oxidized".Does this sound plausible? If so, is there anything
that can be done to save the chemicals or are they forever compromised?
Any and all advise and or suggestions will be appreciated. I hope that I
have provided enough of the facts.
Barbara in Lyme,Ct
potluck@snet.net
Michael Banks on sat 6 mar 99
Very unlikely Babara. Glaze ingredients are inorganic compounds and the
white-firing ones (ie: iron and manganese-free) do not acquire the ability
to produce brown spots by oxidation, hydration or any other reaction brought
about by dampness and time.
Brown spots are caused by iron or manganese minerals. One or more of your
friends ingredients have been contaminated by one of these oxides (rutile,
ilmenite, manganese dioxide, red iron oxide, black iron oxide, yellow ochre,
rust, steel filings etc).
Michael Banks,
Nelson,
New Zealand
-----Original Message-----
>.......(Clip) The glazes using copper carb came out with "brown spots" and
>the glazes using frits are also flawed.She suspects that the chemicals,
>particularly the copper carb,the frits, maybe the gherstly borate have
>somehow absorbed water (though they do not feel damp) or they have
>become "oxidized".....(Clip)
>Barbara in Lyme,Ct
Barbara Long on mon 8 mar 99
Michael
Thanks for your help.We now think that it is possible that the Gherstly
Borate getting damp caused the iron in that ingredient to clump and the
glaze simply needs better sieving.
Barbara in Lyme,Ct
Peter Atwood on wed 10 mar 99
Hi All,
As an aside to the question of whether damp chemicals could cause funky
things to happen to your glaze, one of my studio mates had an
observation. She didn't think it was likely that water could be causing
spotting but mentioned that a little extra water could throw off the
weight of the material. Of course this would lead to an incorrect amount
of material in the glaze formula.
I guess the lesson here would be to avoid using chmeicals that had been
contaminated by any means. Now I'm wondering, are there any glaze
ingredients that are particularly hydroscopic? I've noticed silica
clumping quite a bit.
--Peter Atwood
Get Your Private, Free Email at http://www.hotmail.com
Tom Wirt on thu 11 mar 99
>>>>From: Peter Atwood
>Subject: Damp Chemicals
----------------------------Original message----------------------------
>>Hi All,
>>>I guess the lesson here would be to avoid using chmeicals that had been
contaminated by any means. Now I'm wondering, are there any glaze
ingredients that are particularly hydroscopic? I've noticed silica
clumping quite a bit.
>>>--Peter Atwood
Peter....yes there are hygroscopic materials.....Cornwall stone being a
frequently used one. Recently the Cornwall here changed from light blue to
purplish, and had about 10% extra weight (water). We dried some to find out
the difference from the old batch. With Cornwall, and maybe others, be
careful doing this. Cornwall when truly dry floats like down
feathers.....every where. I have to assume the silica content in this
extremely fine powder is/could be dangerous. (It's why the material is wet
ground in the first place).
Anyway, we tried substituting extra material for the water content, and
didn't notice any difference in the famous moonlight. However, right after
this change, the Gerstley changed and we started having all sorts of
troubles with crawling. Was it the extra water in the Cornwall? Don't
know, but when we take water off the glaze slop and deflocculate properly,
it comes back under control....at least in the last load.
More later.
Tom Wirt
hasebe on thu 11 mar 99
Hi,
Rutile. A bag of rutile was soaked, and I let dry completely. I sieved a
glaze with 80 mesh once. It produced spots all over the pot. Then, I sieved
it twice more with 80 mesh, and spots almost went away.
Hodaka Hasebe
hasebeh@eznet.net (Hodaka Hasebe)
Pittsford, NY
716-264-9698
----------
>From: Peter Atwood
>To: CLAYART@LSV.UKY.EDU
>Subject: Damp Chemicals
>Date: Wed, Mar 10, 1999, 11:09 AM
>
> ----------------------------Original message----------------------------
> Hi All,
>
> As an aside to the question of whether damp chemicals could cause funky
> things to happen to your glaze, one of my studio mates had an
> observation. She didn't think it was likely that water could be causing
> spotting but mentioned that a little extra water could throw off the
> weight of the material. Of course this would lead to an incorrect amount
> of material in the glaze formula.
>
> I guess the lesson here would be to avoid using chmeicals that had been
> contaminated by any means. Now I'm wondering, are there any glaze
> ingredients that are particularly hydroscopic? I've noticed silica
> clumping quite a bit.
>
> --Peter Atwood
> Get Your Private, Free Email at http://www.hotmail.com
>
>
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