Emily Muench on fri 2 apr 99
Can anyone tell me who sells the Tom Coleman commercial glazes......I know
I've seen them advertised in CM but I can't seem to find the ad now.....we
just had a beautiful firing of the Lipstick Purple......someone had a small
amount.....now we're all in love!!!! Thank you!!!
Emily Muench on sat 5 jun 99
I did find the Tom Coleman glazes and his book at Aardvark in
California........thank you to all who directed me there!!!! In the recipe
for his wonderful lipstick purple, iron oxide is called for.........red or
black?????? a look at the batch we have commercially made doesn't give me a
clue, the liquid is a golden color, clearly the rutile...........can anyone
advise me? No e-mail address for Aadvark/Tom Coleman.
Thank you, Emily Muench
Jean Stephenson on sun 6 jun 99
Emily, I don't know either. In some recipes he states _% of yellow iron
oxide, or red iron oxide. Didn't see any black though. Wonder if any of
the glaze gurus could tell if they knew the percentage of colorants were .3
of copper carb, .2 of iron oxide, and .1 of rutile? Best of luck. Jean
----- Original Message -----
From: Emily Muench
To:
Sent: Saturday, June 05, 1999 1:53 PM
Subject: Tom Coleman glaze
> ----------------------------Original message----------------------------
> I did find the Tom Coleman glazes and his book at Aardvark in
> California........thank you to all who directed me there!!!! In the recipe
> for his wonderful lipstick purple, iron oxide is called for.........red or
> black?????? a look at the batch we have commercially made doesn't give me
a
> clue, the liquid is a golden color, clearly the rutile...........can
anyone
> advise me? No e-mail address for Aadvark/Tom Coleman.
> Thank you, Emily Muench
>
Wendy Neilson on sun 6 jun 99
Tom doesn't have e-mail.. can you imagine??!! However, one of his dedicated
students Billye Singer can be reached at billyes@juno.com If she doesn't
have the info you need she can get it.
I have Red Iron Oxide in my notes for this glaze but accuracy is not one of
my strong points so you are best to check it out to be sure.
Try mixing lipstick purple and Vegas red.. half and half.. quite 'squiz'.
(reduction only)
Wendy Neilson, Victoria, BC. Canada
Sharon R Pemberton on sun 6 jun 99
Tom is hawkin' his glaze recipes in an ad in the back of this months CM.
Pug
Tom Buck on tue 8 jun 99
Jean, others:
Many potters writing about copper reds all give approximately the
same advice: namely, that a copper red glaze needs to be a bit runny (ie,
fluid) at the firing cone; that to achieve an adequate red, one needs
nearly 0.5% copper oxide or equal but because copper II oxide is near its
boiling point at C10, and much copper oxide goes to vapour, then the
custom is to double the copper II oxide (or equal) in the glaze, ie, use
0.8-1.0%. As for iron oxide (or tin oxide), it acts as a "catalyst" that
helps speed up the reduction of CuO to Cu2O and Cu metal; one doesn't need
a lot but perhaps up to 1% Fe2O3 (red) is allowable. Rutile would suppkly
the Iron Oxide too and the Titanium IV Oxide that it supplies would have a
minor (perhaps good) effect on the glaze and its colour.
Tom Buck ) tel: 905-389-2339
(westend Lake Ontario, province of Ontario, Canada).
mailing address: 373 East 43rd Street,
Hamilton ON L8T 3E1 Canada
Jean Stephenson on wed 9 jun 99
Thanks for the guide lines. It's nice to have a choice in catalysts.
Always appreciate your knowledge and help. Jean on the OR coast where it is
beautiful today.
----- Original Message -----
From: Tom Buck
To:
Sent: Tuesday, June 08, 1999 2:43 PM
Subject: Re: Tom Coleman glaze
> ----------------------------Original message----------------------------
> Jean, others:
> Many potters writing about copper reds all give approximately the
> same advice: namely, that a copper red glaze needs to be a bit runny (ie,
> fluid) at the firing cone; that to achieve an adequate red, one needs
> nearly 0.5% copper oxide or equal but because copper II oxide is near its
> boiling point at C10, and much copper oxide goes to vapour, then the
> custom is to double the copper II oxide (or equal) in the glaze, ie, use
> 0.8-1.0%. As for iron oxide (or tin oxide), it acts as a "catalyst" that
> helps speed up the reduction of CuO to Cu2O and Cu metal; one doesn't need
> a lot but perhaps up to 1% Fe2O3 (red) is allowable. Rutile would suppkly
> the Iron Oxide too and the Titanium IV Oxide that it supplies would have a
> minor (perhaps good) effect on the glaze and its colour.
>
>
> Tom Buck ) tel: 905-389-2339
> (westend Lake Ontario, province of Ontario, Canada).
> mailing address: 373 East 43rd Street,
> Hamilton ON L8T 3E1 Canada
>
Trabka on thu 10 jun 99
Tom wrote some interesting notes on copper reds. I would take point with
Tom. My history says that .5% is more than adaquet. I sometimes use
less. The reason for the "runny" glazes is to form a glass early in the
firing cycle and seal the copper in the glaze. Reduction is required
from ^015 on up to ^8. I don't think it matters much after ^8. Another
important point is slow cooling.
Tom Buck wrote:
one needs nearly 0.5% copper oxide or equal but because copper II oxide
is near its boiling point at C10, and much copper oxide goes to vapour,
then the custom is to double the copper II oxide (or equal) in the
glaze, ie, use 0.8-1.0%. As for iron oxide (or tin oxide), it acts as a
"catalyst" that helps speed up the reduction of CuO to Cu2O and Cu
metal;
Tom Buck on fri 11 jun 99
Ms ? or Mr ? Trabka:
Let's agree that 0.5% CuO (copper II oxide, black oxide) is
"adequate" to form the Cu2O/Cu metal combination that gives the pot its
red colour.
What needs agreement is how the reduction of CuO (loss of one
copper atom per two molecules of CuO) comes about.
In most cases, the copper oxide is introduced into the glaze
slurry as copper II carbonate basic [CuCO3.Cu(OH)2], the green powder
familiar to most, and this crystalline material, as fine powder, is
dispersed throughout the glass-forming components of the glaze. When the
glaze coat is heated beyond 200 oC, the copper compound changes to CuO,
releasing CO2 and H2O.
To convert CuO to red oxide and metal, it is necessary that the
CuO molecules (stay-put on the surface until the glaze becomes liquid)
come into contact with reducing agents, usually carbon IV oxide (CO) and
Hydrogen (H2), and both these agents are gases. So, the copper red glaze,
it would seem, requires that intimate contact be initially made between
surface solids and gases resulting from combustion. Interaction between
solids and gases is slow and uncertain in such a retort as a pottery kiln.
However, if the glaze became liquid, then the roiling action would
increase reaction speed many times, 10-fold or more.
Most people who have written about copper reds prefer to shift the
kiln into a reducing condition at 1000 oC and continue that way until Cone
10 (or higher) is reached. Then some do a brief soak under oxidizing
conditions and shut-down. Others find the kiln is leaky enough for
re-oxdiation to occur as the kiln cools.
Now, there has been little work done (to my reading ability) on
whether good reds are formed early on in the reduction period, or later
when the glaze has formed liquid. My own suspicion, based on limited
tests, is that most of the Cu2O/Cu metal is generated at close to the
final firing Cone, ie, when a liquid phase is present. If the base glaze
is formulated to be fluid at C9/10 --the Seger would range as follows:
SiO2 3.0-4.0 (high max of 5.0)
Al2O3 0.30 - 0.45 (max 0.6)
CaO 0.50 - 0.60
MgO (trace, 0.01/02)
KNaO 0.30 - 0.45 plus small amounts of other flux oxides.
But not all bases follow this pattern; for example, Ron Roy has published
this copper red glaze (for his own use?):
CaO 0.33; MgO 0.14; SrO 0.31; KNaO 0.22; Al2O3 0.27; SiO2 2.68
and this should be molten at C6/7. But the refractory nature of MgO and
SrO will hold the viscosity in a range suitable for C10.
Some mixes contain 0.2 -0.3 B2O3 to enhance the melting and lower
the viscosity.
If most red is formed at C9/10, then extra Copper compound should
be added to offset the loss of this component in the flue gases.
Many potters are both attracted by the colour and by the mystique
of the glaze itself. As often repeated on Clayart, this is a troublesome
glaze that demands a good base glaze to begin with, then proper
application of the glaze coat, followed by precise control over kiln
operations. If Tom Coleman has a secret, it is not the glaze recipe he
offers to all comers, but the kiln he has and his skill in running it
carefully and consistently.
Tom Buck ) tel: 905-389-2339
(westend Lake Ontario, province of Ontario, Canada).
mailing address: 373 East 43rd Street,
Hamilton ON L8T 3E1 Canada
On Thu, 10 Jun 1999, Trabka wrote:
> ----------------------------Original message----------------------------
> Tom wrote some interesting notes on copper reds. I would take point with
> Tom. My history says that .5% is more than adaquet. I sometimes use
> less. The reason for the "runny" glazes is to form a glass early in the
> firing cycle and seal the copper in the glaze. Reduction is required
> from ^015 on up to ^8. I don't think it matters much after ^8. Another
> important point is slow cooling.
>
> Tom Buck wrote:
> one needs nearly 0.5% copper oxide or equal but because copper II oxide
> is near its boiling point at C10, and much copper oxide goes to vapour,
> then the custom is to double the copper II oxide (or equal) in the
> glaze, ie, use 0.8-1.0%. As for iron oxide (or tin oxide), it acts as a
> "catalyst" that helps speed up the reduction of CuO to Cu2O and Cu
> metal;
>
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