Erin Hayes on tue 18 nov 97
Hello All!
One of my students has been testing the numerous Black matte glaze
formulas generously provided by Clayart people, and we have found one we
all really love. Don Goodrich sent it to us.
BLACKSMITH (formulated by Tony Holmes)
Custer 54
Dolomite 18
Whiting 3
EPK 30
105 (acknowledged by Don as weird, but the glaze does
work)
Mn Ox 2
Co Carb 3
Cr Oxide 1
RIO 4
Bentonite 3
The glaze is a lovely, pitch-black satin. It's one of those textures
you just want to pick up and fondle, you know? The problem is that I try
to stay away from Mn as a rule in the classroom studio.
I wanted to ask you all if you personally (or professionally) would be
comfortable using a 2%Mn glaze in a satin base - at least for use in
funcational ware. Do you feel it is any worse than Cobalt? This glaze
is sooooo luscious - I really would like to add it to the inventory, but
I don't want to run into any trouble with the Mn.
Any and all ideas are welcome - please reply off-list...
Erin.
Craig Martell on wed 19 nov 97
Hi Erin:
I apologize for not following your instructions and responding off the list
but I didn't feel comfortable doing that. I think this kind of stuff is of
interest to all on the list. OK you guys, let me know if I'm wrong about this.
The Blacksmith glaze is too low in silica to be considered safe for
functional ware. There is also an oversupply of alumina. The SiO2 in the
glaze has to deal with all the metal oxides and they add up to 10%. You
wouldn't want chrome, manganese, or cobalt to leach. Also, this is a
magnesia-alumina matt. Magnesia will form matt glazes by reacting with the
silica to form enstatite crystals and relies on devitrification. Alumina
produces mattness by retarding fusion somewhat and further compounds the low
silica vs. metal oxide problem. Also, I'm assuming that this is a cone 10 glaze.
Personally, I wouldn't use this glaze for functional pots even if the silica
was above the lower limit. A black glaze is saturated with coloring oxides
and you have to be careful with them. The only metal that I will saturate a
glaze with for functional ware is Iron. I am just stating my own feelings
here, based on what I know about high fire glazes.
regards, Craig Martell-Oregon
Marcia Kindlmann on thu 20 nov 97
Subject: Seeking Mn glaze advice
Erin Hayes writes about the "Blacksmith" glaze which has 3 CoCO3, 2 Manganese
Oxide and 1 Cr oxide,
> The glaze is a lovely, pitch-black satin. It's one of those textures
> you just want to pick up and fondle, you know? The problem is that I try
> to stay away from Mn as a rule in the classroom studio.
>
> I wanted to ask you all if you personally (or professionally) would be
> comfortable using a 2%Mn glaze in a satin base - at least for use in
> funcational ware. Do you feel it is any worse than Cobalt? This glaze
> is sooooo luscious - I really would like to add it to the inventory, but
> I don't want to run into any trouble with the Mn.
>
> Any and all ideas are welcome - please reply off-list...
Erin,
This is a fascinating topic and I would like to know more about
(1) whether a glazes like you describe could be developed without Mn
--and without Chrome as well-- and
(2) whether anyone has done the kind of (expensive) metals-release
testing for dinnerware that would show whether such a glaze as
"Blacksmith" releases nothing harmful. And if so, what glaze, on
what clay, fired to what temp, what reduc/ox conditions, etc. etc.
Would Barnard clay (aka Blackbird) be a promising material for a
satin-black glaze that would enable students to avoid handling the
Mn & the Cr? I tried Barnard 85% with Neph Sy 15% and got a velvety
but stony-matt black glaze. More Neph Sy, more satin?
But -- does Barnard get its blackness from just those metals you're
concerned about?
If so, is it any safer to handle Barnard, or use it on dinnerware,
when such metals are in a clay matrix instead of in pure form? Lotsa
questions. Looking forward to enlightenment from more technically
expert people than..
Marcia
Erin Hayes on thu 20 nov 97
Hello all!
After numerous inquiries about this post from yesterday, I figured I'd
better get a clue and post the atmosphere and cone! Helpful, huh?!
The glaze is a Cone 10 Reduction, and seems to looks its most delicious when
applied a little heavy. Mmm-Mmm-Mmm! (Not so Mmm-Mmm-Mmm due to the
Manganese I guess.)
> BLACKSMITH (formulated by Tony Holmes)
> Custer 54
> Dolomite 18
> Whiting 3
> EPK 30
> 105 (acknowledged by Don Goodrich as weird, but the glaze does
> work)
>
> Mn Ox 2
> Co Carb 3
> Cr Oxide 1
> RIO 4
> Bentonite 3
>
> The glaze is a lovely, pitch-black satin. It's one of those textures
> you just want to pick up and fondle, you know?
Better luck now that all the pertinent info is there...
Erin.
Eleanora Eden on thu 20 nov 97
Hi Erin and all,
There is no temperature ID on this glaze. I know this has been discussed
alot. It would be SO GREAT if each glaze posted on clayart had its cone
designation as part of the recipe name, rather than somewhere in the
accompanying text. I take it by the recipe that it's some kind of highfire....
TIA.....
At 03:01 PM 11/18/97 EST, you wrote:
>----------------------------Original message----------------------------
>Hello All!
>
>One of my students has been testing the numerous Black matte glaze
>formulas generously provided by Clayart people, and we have found one we
>all really love. Don Goodrich sent it to us.
>
>BLACKSMITH (formulated by Tony Holmes)
>Custer 54
>Dolomite 18
>Whiting 3
>EPK 30
> 105 (acknowledged by Don as weird, but the glaze does
>work)
>
>Mn Ox 2
>Co Carb 3
>Cr Oxide 1
>RIO 4
>Bentonite 3
>
>The glaze is a lovely, pitch-black satin. It's one of those textures
>you just want to pick up and fondle, you know? The problem is that I try
>to stay away from Mn as a rule in the classroom studio.
>
>I wanted to ask you all if you personally (or professionally) would be
>comfortable using a 2%Mn glaze in a satin base - at least for use in
>funcational ware. Do you feel it is any worse than Cobalt? This glaze
>is sooooo luscious - I really would like to add it to the inventory, but
>I don't want to run into any trouble with the Mn.
>
>Any and all ideas are welcome - please reply off-list...
>
>Erin.
>
>
Eleanora Eden 802 869-2003
Paradise Hill
Bellows Falls, VT 05101 eden@sover.net
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