Jeff Lawrence on wed 8 apr 98
Hello all,
I've been playing with ^5 reduction firing, shooting for repeatable copper
reds. I read Karl Platt's articulo on Tony Hansen's website and got some
usefu info from Tom Buck. Results have been blushing with potential, one
might say, but I am plagued by that guy in that kiln ad. Enough that I
bought his book, "Glazes I use" by Tom Coleman.
Some things I would appreciate experienced comments on are:
(1) what rate of cooling works? The upshot of most things I've read is
"slow, but not too slow." Or sometimes "fast, but not too fast." Anybody
ever charted it?
(2) why would Tom Coleman say firings shouldn't last more than 12-14 hours?
just the tin oxide volatalizes? He makes me suspicious of my candling to
700F overnight, but I'd rather continue in it for single firing's sake.
Karl Platt's comments on the function of tin oxide -- glomming up the
valencies on the Cu2O too keep it from turning into something ugly -- made
some sense when I read them, though I should probably re-read. However, the
function of the three other materials remains mysterious:
(1) zinc oxide
(2) an excess of silica
(3) iron oxide.
I've come across unelaborated comments in my reading that they assist in the
formation of copper reds. Can any of you
chemists/physicists/crystallographers throw some light on why they might?
Testing a base glaze tomorrow with the three mystery puppies ... or are they
red herrings?
Thanks in advance!
Jeff
Jeff Lawrence
jml@sundagger.com
Sun Dagger Design
Rt 3 Box 220
Espanola, NM 87532
ph 505-753-5913
Alexander Solla on thu 9 apr 98
Jeff-
Here's my 2 cents on copper reds: zinc is not neccesary but can compliment
a copper red. In my experience what it really does is lower the Melting point
of a glaze otherwise overloaded with too high a melting spar. So, fix this with
using a high temp frit instead.
Silica is in there so that there's plenty of glass. Without sufficient glass
there wont be a red. AS it tends towards anything less than gloss, the
color turns first livery, then pink and finally like crushed strawberries.
Read Tichane's chapter about copper red glasses. Nice!
ANd lastly Iron: iron and tin and copper are essential. The iron and tin
work together with the copper in a redox equation. This means that the
tin and iron are more easily reoxidized than copper so they continue stealing
the oxygen from the copper. But, the easiest way to prove this to yourself
is to take a fluid glaze, high is silica with a frit like 3110 or pemco 25 and
then add 1% copper carb. Fire it. Then do a second test with 1% copper carb
and 2% tin and fire. Do a third test adding .5% copper, 1% tin, 1% iron. Fire
and keep great notes.
There is a real incredible range that reds can be made in. From crushed
strawberries (non-fluid) to oxblood (megafluid), there is a ton of variety.
So, test away.
As for getting it to work at c/6... shouldn't be a problem. I regularly get
Cu Reds especially in high frit glazes. Firing time is a personal issue and
of yet I can't give a definite schedule. Consider that the firing time is an
issue because Cu is volatile. So fire fast, get it melted and cooling quick.
This is also true considering how fluid these glazes can be. Cooling though,
should be fast enough to prevent the Copper crystal from growing too much.
Essentially, if copper is cooled fast it will remain in its reduced state.
See Tichane's diagram of the colloidal color layers. BUT if the reds are
slow cooled you will find muddy reds to brown liver colors. This is due to
crystal formation. Too fast will be almost colorless. Try pulling a test tile
from a kiln with Cu red on it, and it will be clear at c/10. BUt let it cool
to about 1800 F and then pull. Cool again to 1200F and pull. THis help figure
out the schedule for your kiln and your glaze and body.
Good luck and have fun!
Alex Solla in Utah
slpbm@cc.usu.edu
David Hendley on thu 9 apr 98
Jeff, I'm not a chemist or scientist,
but I know how to produce copper reds.
Here are my opinions, based on my experience:
Cooling, within a reasonable range, doesn't matter.
I cool from ^10 to 'warm' over 36-40 hours.
Firing (heating) should be very fast.
I don't think candling overnight really matters because
the temperatures are so low.
I fire bisque ware from 0 to ^10 in 7 or 8 hours.
Functions of your 3 materials,
1) Zinc oxide does nothing.
I have done side by side tests with zinc oxide and, in my opinion,
it contributes nothing to copper red glazes.
2) A typical copper red glaze has a silica content within
the limit formulas for your temperature range.
Tom Coleman's 'Vegas Red', as printed in Clay Times magazine,
is seriously low in both alumina and silica, and would definitely
be 'suspect' as far as durability and use on food surfaces.
3) According to Robert Tichane, in his 'copper reds' book, iron oxide has
historically been used in much the same way as tin oxide is now
used, to facilitate the color development. The problem, of course,
is that iron oxide also 'pollutes' the pure copper color by adding
its own hue.
David Hendley
Maydelle, Texas
hendley@sosweb.net
At 12:12 PM 4/8/98 EDT, you wrote:
>----------------------------Original message----------------------------
>Hello all,
>
>I've been playing with ^5 reduction firing, shooting for repeatable copper
>reds. I read Karl Platt's articulo on Tony Hansen's website and got some
>usefu info from Tom Buck. Results have been blushing with potential, one
>might say, but I am plagued by that guy in that kiln ad. Enough that I
>bought his book, "Glazes I use" by Tom Coleman.
>
>Some things I would appreciate experienced comments on are:
>
>(1) what rate of cooling works? The upshot of most things I've read is
>"slow, but not too slow." Or sometimes "fast, but not too fast." Anybody
>ever charted it?
>
>(2) why would Tom Coleman say firings shouldn't last more than 12-14 hours?
>just the tin oxide volatalizes? He makes me suspicious of my candling to
>700F overnight, but I'd rather continue in it for single firing's sake.
>
>
>
>Karl Platt's comments on the function of tin oxide -- glomming up the
>valencies on the Cu2O too keep it from turning into something ugly -- made
>some sense when I read them, though I should probably re-read. However, the
>function of the three other materials remains mysterious:
>(1) zinc oxide
>(2) an excess of silica
>(3) iron oxide.
>I've come across unelaborated comments in my reading that they assist in the
>formation of copper reds. Can any of you
>chemists/physicists/crystallographers throw some light on why they might?
>
>Testing a base glaze tomorrow with the three mystery puppies ... or are they
>red herrings?
>
>Thanks in advance!
>Jeff
>Jeff Lawrence
>jml@sundagger.com
>Sun Dagger Design
>Rt 3 Box 220
>Espanola, NM 87532
>ph 505-753-5913
>
Talbott on thu 9 apr 98
A) Cool as slow as your kiln will allow... I usually cool for 60 hrs
before opening our 45 cu ft kiln after a ^10 firing..
B) Copper volatizes so I try to keep the entire firing time to 16 hrs or less..
Iron tends to muddy up copper reds so typically I avoid using copper..
I will leave a pic of a "good" copper red at the Glaze Composition - High
Fire board at http://www.PotteryInfo.com
I am still considering a virtual gallery at my web-site...
>----------------------------Original message----------------------------
>Hello all,
>
>I've been playing with ^5 reduction firing, shooting for repeatable copper
>reds. I read Karl Platt's articulo on Tony Hansen's website and got some
>usefu info from Tom Buck. Results have been blushing with potential, one
>might say, but I am plagued by that guy in that kiln ad. Enough that I
>bought his book, "Glazes I use" by Tom Coleman.
>
>Some things I would appreciate experienced comments on are:
>
>(1) what rate of cooling works? The upshot of most things I've read is
>"slow, but not too slow." Or sometimes "fast, but not too fast." Anybody
>ever charted it?
>
>(2) why would Tom Coleman say firings shouldn't last more than 12-14 hours?
>just the tin oxide volatalizes? He makes me suspicious of my candling to
>700F overnight, but I'd rather continue in it for single firing's sake.
>
>
>
>Karl Platt's comments on the function of tin oxide -- glomming up the
>valencies on the Cu2O too keep it from turning into something ugly -- made
>some sense when I read them, though I should probably re-read. However, the
>function of the three other materials remains mysterious:
>(1) zinc oxide
>(2) an excess of silica
>(3) iron oxide.
>I've come across unelaborated comments in my reading that they assist in the
>formation of copper reds. Can any of you
>chemists/physicists/crystallographers throw some light on why they might?
>
>Testing a base glaze tomorrow with the three mystery puppies ... or are they
>red herrings?
>
>Thanks in advance!
>Jeff
>Jeff Lawrence
>jml@sundagger.com
>Sun Dagger Design
>Rt 3 Box 220
>Espanola, NM 87532
>ph 505-753-5913
http://www.PotteryInfo.com
101 CLAYART MUGS (Summer 1998)
2ND ANNUAL CLAYARTERS' GALLERY - NAPLES, MAINE (Summer 1998)
E-MAIL ME FOR APPLICATIONS
Celia & Marshall Talbott, Pottery By Celia, Route 114, P O Box 4116,
Naples, Maine 04055-4116,(207)693-6100 voice and fax,(call first)
---------------------------------------------------------------------
John Britt on sat 11 apr 98
David,
It is my understanding (Hammer, and Currie) that ZNO volitalizes in a
reducing atomsphere. So in achieving Copper Red it should not be
helpful.
--
John Britt
claydude@unicomp.net
Dys-Functional Pottery
Dallas, Texas
http://www.dysfunctionalpottery.com/claydude
David Hendley on sun 12 apr 98
Whether zinc volitalizes in reduction is an area of disagreement.
For instance, take a look at Rhodes' "Clay & Glazes for the Potter".
Tichane also quotes sources that suggest using zinc oxide in
his "Copper Reds" book.
My experiments indicate that, no, zinc oxide does nothing to
facilitate copper red development.
David Hendley
Maydelle, Texas
At 10:53 AM 4/11/98 EDT, you wrote:
>----------------------------Original message----------------------------
>David,
>
>It is my understanding (Hammer, and Currie) that ZNO volitalizes in a
>reducing atomsphere. So in achieving Copper Red it should not be
>helpful.
>--
>John Britt
>claydude@unicomp.net
>Dys-Functional Pottery
>Dallas, Texas
>http://www.dysfunctionalpottery.com/claydude
>
David Hendley
Maydelle, Texas
hendley@sosweb.net
rballou@mnsinc.com on tue 14 apr 98
I've put a teaspoon of raw zinc on a test tile in a reduction firing.
Nothing's there at the end of the firing. Perhaps a line blend with a spar,
fired in both oxidation and reduction, would yield some additional
information as it relates to Tom Buck's additional post on this subject.
Ruth Ballou
rballou@mnsinc.com
>----------------------------Original message----------------------------
>Whether zinc volitalizes in reduction is an area of disagreement.
>For instance, take a look at Rhodes' "Clay & Glazes for the Potter".
>Tichane also quotes sources that suggest using zinc oxide in
>his "Copper Reds" book.
>
>My experiments indicate that, no, zinc oxide does nothing to
>facilitate copper red development.
>
>David Hendley
>Maydelle, Texas
>
>
>At 10:53 AM 4/11/98 EDT, you wrote:
>>----------------------------Original message----------------------------
>>David,
>>
>>It is my understanding (Hammer, and Currie) that ZNO volitalizes in a
>>reducing atomsphere. So in achieving Copper Red it should not be
>>helpful.
>>--
>>John Britt
>>claydude@unicomp.net
>>Dys-Functional Pottery
>>Dallas, Texas
>>http://www.dysfunctionalpottery.com/claydude
>>
>David Hendley
>Maydelle, Texas
>hendley@sosweb.net
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