Smith, Judy on mon 14 jan 08
Some time ago I wrote to the list about having problems with Red Iron
Oxide. When I top coated it with a clear glaze, it no longer showed up
on my pots. Several people wrote back that maybe the calcium in my
clear glaze was changing the RIO and making it appear to vanish. I need
the recipe for a clear glaze that has little or no calcium so that I can
test this. Can someone please give me a clear cone 6 oxidation glaze
recipe that contains little or no calcium?
=20
Thanks,
Judy Smith
John Sankey on tue 15 jan 08
"Some time ago I wrote to the list about having problems with Red Iron
Oxide. When I top coated it with a clear glaze, it no longer showed up
on my pots. Several people wrote back that maybe the calcium in my
clear glaze was changing the RIO and making it appear to vanish. I need
the recipe for a clear glaze that has little or no calcium so that I can
test this. Can someone please give me a clear cone 6 oxidation glaze
recipe that contains little or no calcium?"
First, my work with iron glazes indicates that it is the silica
in your overglaze that is the culprit, forming ferrosilate which
is an almost transparent yellow. Iron reds are only red on the
top surface exposed to oxygen below 1000C.
Second, I'm trying to make a calcia and magnesia-free iron glaze
to test the effects of each separately and am having a lot of
problems finding materials. Almost all frits contain calcia
except a few that are very high in boron and low in alkalis and
sources of calcia-free alkalis all seem to be soluble. So, unless
you're a researcher, you're pretty well stuck with calcia.
--
Include 'Byrd' in the subject line of your reply
to get through my spam filter.
Ron Roy on thu 17 jan 08
Hi Judy,
I don't think you need no Calcium - maybe less will do.
Shino type glazes have little calcium.
I see several Fusion frits that have no calcium by the way - and strontium
seems to enhance iron colour.
Frit 3110 has only 6.3 calcium and 3249 only has 3.5% - I'll bet you can
make a glaze with either of those ferro frits with very little CaO.
Let me know if you can get either - or any low calcium frit and I'll make
up a few for you.
RR
>Some time ago I wrote to the list about having problems with Red Iron
>Oxide. When I top coated it with a clear glaze, it no longer showed up
>on my pots. Several people wrote back that maybe the calcium in my
>clear glaze was changing the RIO and making it appear to vanish. I need
>the recipe for a clear glaze that has little or no calcium so that I can
>test this. Can someone please give me a clear cone 6 oxidation glaze
>recipe that contains little or no calcium?
>
>
>
>Thanks,
>
>Judy Smith
>
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Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
John Sankey on fri 18 jan 08
Fusion frit 367 has no calcium - Spectrum glazes in Toronto sells
it retail. I've got some and will be using it in iron glaze tests
shortly. But, it has too little alkali to use by itself, so you
have to find a calcia-free source of them to get sufficient flux.
Nepheline syenite has 14.4 alkali vs. 0.7 calcia, but too much
alumina to suffice for a cone 6 glaze. The only ones I've found
with sufficient alkali are water-soluble, so I'm going to have
to rely on olive oil as the solvent. That will be no problem on
horizontal test tiles, but I've no idea how it would work to
stick glaze to normal pottery surfaces.
A: frit,Fusion 367
E: 7.8 Na2O
E: 38.4 B2O3
E: 53.8 SiO2
--
Include 'Byrd' in the subject line of your reply
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Smith, Judy on fri 18 jan 08
Thank you Ron Roy and John Sankey for your helpful information about my
RIO problems. John Sankey tells me that my problem may be a reaction of
the silica in my glaze (not the calcium).
I paint a RIO and water mixture onto my bisqued pots and it gives me a
nice warm brown color (especially where it is thicker in the textured
areas). This looks very nice as long as I fire it to ^6 with no glaze.
When I apply Coyote clear glaze over the RIO, the nice brown color
disappears and I am left with a yellowish transparent glaze over my
white B-mix clay.
I am looking for a glaze that will make the pot watertight without
changing the brown color of the RIO. I thought all glazes had silica in
them. Do you have any ideas on how to solve this problem?
Thanks,
Judy Smith=20
-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG] On Behalf Of Ron Roy
Sent: Wednesday, January 16, 2008 11:04 PM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Re: need cone 6 clear glaze without calcium
Hi Judy,
I don't think you need no Calcium - maybe less will do.
Shino type glazes have little calcium.
I see several Fusion frits that have no calcium by the way - and
strontium
seems to enhance iron colour.
Frit 3110 has only 6.3 calcium and 3249 only has 3.5% - I'll bet you can
make a glaze with either of those ferro frits with very little CaO.
Let me know if you can get either - or any low calcium frit and I'll
make
up a few for you.
RR
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