vince pitelka on sun 24 feb 02
> (a)"Since the breakdown of carbon or sulfur compounds in body and
glaze
> so easily reduces iron, a slow and very thoroughly oxidizing
> atmosphere is critical through the 700-900C range to assure that
all
> the iron remains in its antiflux oxidized form."
Jim -
This is true, and it is very important to avoid early glassy phase and
resulting carbon and/or sulphur coring. That is always a concern, but if
you include 20% red iron in your claybody your problem will occur at higher
temperatures. Red iron oxide dissociates to black iron oxide above 2100F
(I believe I have that temperature right, but I might be off by a bit.) in
both oxidation and reduction, so it WILL become an active flux before
maturation temperature, and the 20% will pretty much melt your claybody.
You might try developing the color with a mixture of red iron oxide,
blackbird/barnard slip clay, and redart clay. Do lots of tests.
Best wishes -
- Vince
Vince Pitelka
Appalachian Center for Crafts
Tennessee Technological University
1560 Craft Center Drive, Smithville TN 37166
Home - vpitelka@dtccom.net
615/597-5376
Work - wpitelka@tntech.edu
615/597-6801 ext. 111, fax 615/597-6803
http://www.craftcenter.tntech.edu/
WHC228@AOL.COM on sun 24 feb 02
Jim
I would make up some small tests and fire them with your regular work until
you work it out.
Snail Scott on sun 24 feb 02
At 03:03 PM 2/23/02 -0600, you wrote:
>I want to slipcast...without using brown slip...,
>So, I'm thinkin' maybe I can mix 20% Red Iron Oxide...
So, what's the difference? Don't you still end up
with brown slip?
That's a hellacious lot of RIO, too. Why?
-Snail
Jim Murphy on sun 24 feb 02
Thanks Vince, Bill and Snail for your replies.
Let me also share the following information I gathered from Digitalfire's
website regarding Iron Oxide:
(a)"Since the breakdown of carbon or sulfur compounds in body and glaze
so easily reduces iron, a slow and very thoroughly oxidizing
atmosphere is critical through the 700-900C range to assure that all
the iron remains in its antiflux oxidized form."
(b)"Iron bearing clays fire much darker in reduction than oxidation. In
addition, reduction fired iron bodies experience sudden color changes
from red or tan to dark brown across a narrow temperature range
characteristic to each formulation."
Since I've chosen very clean (low-Iron) Kaolins and a relatively clean Ball
Clay blend for use in my porcelain casting slip, my thinking was I'd need
more Red Iron Oxide to get a darker brown color since I'm firing in an
electric kiln in oxidation.
I'd like the fired "head" to be a dark chocolate (not milk chocolate) brown.
However, I'll heed your advice and try smaller percentages of Red Iron Oxide
in smaller cast "test pieces" to see if I can get the dark brown color I
desire.
Perhaps a "dark chocolate brown" is not possible with Red Iron Oxide alone
in oxidation.
Thanks again for your most helpful suggestions.
Jim Murphy
Jim Murphy on mon 25 feb 02
Vince & Snail,
Thanks once again for your suggestions.
on 2/24/02 11:00 PM, vince pitelka at vpitelka@DTCCOM.NET wrote:
> You might try developing the color with a mixture of red iron oxide,
> blackbird/barnard slip clay, and redart clay. Do lots of tests.
Vince, this makes very good sense, however, for now I need to stick with the
clays I have in my casting slip recipe and try to get the dark chocolate
brown body color using oxides, and if all oxide testing fails, then I'll go
to a commercial body stain.
on 2/25/02 11:25 AM, Snail Scott at snail@MINDSPRING.COM wrote:
> Add some manganese; it'll help make it darker.
Snail, my testing will include using R.I.O, MnO2 and Cobalt Oxide together
to get a black (in oxidation) body color, so it seems logical that using
MnO2 with R.I.O. may yield a dark brown color.
It appears my tests need to include lower percentages of R.I.O. together
with MnO2 (1-2%). I am aware of the toxicity of MnO2 and that it dissociates
to MnO around 1080 C.
I need to test test test !
Thanks again,
Jim Murphy
Snail Scott on mon 25 feb 02
At 07:26 PM 2/24/02 -0600, you wrote:
>Perhaps a "dark chocolate brown" is not possible with Red Iron Oxide alone
>in oxidation.
Add some manganese; it'll help make it darker.
-Snail
Ron Roy on tue 26 feb 02
Fe2O3 is only reduced to FeO in a reducing atmosphere - Fe2O3 is not much
as a flux compared to FeO - a strong flux starting at about 700C.
Watch out for Barnard - it has a fair amount of MnO2 - vent well.
RR
>This is true, and it is very important to avoid early glassy phase and
>resulting carbon and/or sulphur coring. That is always a concern, but if
>you include 20% red iron in your claybody your problem will occur at higher
>temperatures. Red iron oxide dissociates to black iron oxide above 2100F
>(I believe I have that temperature right, but I might be off by a bit.) in
>both oxidation and reduction, so it WILL become an active flux before
>maturation temperature, and the 20% will pretty much melt your claybody.
>You might try developing the color with a mixture of red iron oxide,
>blackbird/barnard slip clay, and redart clay. Do lots of tests.
Ron Roy
RR# 4
15084 Little Lake Rd..
Brighton,
Ontario, Canada
KOK 1H0
Residence 613-475-9544
Studio 613-475-3715
Fax 613-475-3513
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