Bill Amsterlaw on wed 26 nov 97
Hi Marshall and Clayart:
You use an iron-bearing clay body and start reduction very early and hold
it through the entire firing. This would seem to invite a problem with
black coring. Have you had a problem with black coring when you fire this
way?
- Bill Amsterlaw (wamster@slic.com)
Plattsburgh, NY
>>
We have fairly good success firing copper reds using stoneware as the
claybody... we bisque fire to ^06 and then glaze fire to ^9/10.... during
the glaze fire (gas kiln) I go into reduction around ^015 about 800 degrees
Celsius, "oxyprobe" around .67 and I stay in reduction at that same reading
until I reach ^9/10.. I then shut the kiln down and immediately close the
damper, cover the burner ports, peeps in, etc... close it up "tight" and
let the kiln COOL SLOWLY for about 60 hours prior to opening the kiln... I
would never consider firing without using an oxyprobe. ...Marshall
<<
Talbott on thu 27 nov 97
Bill... Never a problem with black coring...We twice fire and we bisque to
^06 in oxidation and the glaze fire in oxidation to about ^015 or ^010 and
then go into reduction as described below... Marshall
>----------------------------Original message----------------------------
>Hi Marshall and Clayart:
>
>You use an iron-bearing clay body and start reduction very early and hold
>it through the entire firing. This would seem to invite a problem with
>black coring. Have you had a problem with black coring when you fire this
>way?
>
>- Bill Amsterlaw (wamster@slic.com)
> Plattsburgh, NY
>
>>>
>We have fairly good success firing copper reds using stoneware as the
>claybody... we bisque fire to ^06 and then glaze fire to ^9/10.... during
>the glaze fire (gas kiln) I go into reduction around ^015 about 800 degrees
>Celsius, "oxyprobe" around .67 and I stay in reduction at that same reading
>until I reach ^9/10.. I then shut the kiln down and immediately close the
>damper, cover the burner ports, peeps in, etc... close it up "tight" and
>let the kiln COOL SLOWLY for about 60 hours prior to opening the kiln... I
>would never consider firing without using an oxyprobe. ...Marshall
><<
Ron Roy on thu 27 nov 97
Hi Bill,
Guess you have to define what you mean by black coring - bloating? or
different shades of gray and/or black in the body cross section.
This is the way I fire (see below) and - although I use mostly porcelain. I
also fire hundreds of clay samples (body and basic clays) for a local clay
maker. These bars are 6" long, 1" wide and 1/2" thick. They range from
porcelain to bodies with lots of fireclay and iron bearing clay - and never
get a bloat. When the bars are broken they are an even gray (the more iron
the grayer up to black) all the way through. What you are referring to
(black core) is a problem which happens because of improper bisque firing.
Not enough oxygen to burn off organics between 700C and 900C.
I'm no beginner with this (735 firing to date in my gas kiln) - keeping a
kiln in reduction from 800C to 1260C is not a problem and my tenmoku sure
likes it. If I were once firing I would be very careful to make sure the
organics were oxidized before I went into reduction.
There were reds in my kiln today (I do custom firing) and I didn't get into
reduction till after 900C this time. In fact I have had reds when I didn't
get into reduction till after 1000C - but I suspect this may have to do
with different formulations - I think coppers like early reduction.
>You use an iron-bearing clay body and start reduction very early and hold
>it through the entire firing. This would seem to invite a problem with
>black coring. Have you had a problem with black coring when you fire this
>way?
>
>- Bill Amsterlaw (wamster@slic.com)
> Plattsburgh, NY
>
>>>
>We have fairly good success firing copper reds using stoneware as the
>claybody... we bisque fire to ^06 and then glaze fire to ^9/10.... during
>the glaze fire (gas kiln) I go into reduction around ^015 about 800 degrees
>Celsius, "oxyprobe" around .67 and I stay in reduction at that same reading
>until I reach ^9/10.. I then shut the kiln down and immediately close the
>damper, cover the burner ports, peeps in, etc... close it up "tight" and
>let the kiln COOL SLOWLY for about 60 hours prior to opening the kiln... I
>would never consider firing without using an oxyprobe. ...Marshall
><<
Ron Roy
93 Pegasus Trail
Scarborough,Canada
M1G 3N8
Evenings, call 416 439 2621
Fax, 416 438 7849
Studio: 416-752-7862.
Email ronroy@astral.magic.ca
Home page http://digitalfire.com/education/people/ronroy.htm
Talbott on fri 28 nov 97
Bill...
Yes at this point we fire all of our glazes this way.. Most all
colorants to my knowledge including copper, cobalt, chromium, iron,
titanium, etc... all produce more brilliant colors when fire in a reducing
atmosphere...
If I ever get around to firing crystalline glazes then I will fire them in
oxidation.
Happy Thanksgiving... Marshall
>Hi Marshall:
>
>Thanks for the reply. Do you fire all your glazes this way or just the
>copper reds?
>
>- Bill Amsterlaw (wamster@slic.com)
> Plattsburgh, NY
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