Lili Krakowski on tue 7 oct 08
First I ran the glaze through Glaze Master (TM)., naming it
WhyBlue Glaze
.305 Na2O
.066 K2O
.003 MgO
.626 CaO
1.000 Total
.297 Al2O3
.371 B2O3
.002 Fe2O3
3.815 SiO2
.002 TiO2
I think, by the way, that the recipe could be simplified.
However. It is a calcium borate glaze, with soda as the primary
extra flux.
I have had several times blue glazes resulting from iron and
boron. I have a set of small bowls with a lovely blue glaze that
never even heard of cobalt. So my guess here is that the iron
chromate provided enough iron for that blue, that the chrome did
not "distract" from it--and that in other instances the copper
undid the blue and
made the whole thing green.
I would love to see the same glaze tested with just 2% or so of
iron.
If the underlying body contains iron- that would contribute to
the effect.
Lili Krakowski
Be of good courage
Bill Merrill on tue 7 oct 08
Perhaps beside the boron in the glaze, the chrome in Iron chromate helps
contribute to the bluish color.
=20
Iron chromate is a dense compound of iron and chromium.
It is used in glazes to produce gray, brown, or black depending on the
base glaze and percentage and other coloring oxides present. It is often
used in underglazes, engobes and clay bodies.
The sodium content in the RO column is about the same as the B2O3
column, which in combination with the high calcium count greatly affects
the color.
It isn't surprising the glaze is bluish in nature. What are the batch
figures. What specific spar was used? Where did the MgO come from? Was
there some dolomite used? Magnesium carbonate? What was the main source
of calcium"? Whiting? I think it's quite interesting to deal with
numbers, but seeing the material that are in the glazes may be of more
interest. It's great people take such an interest in working on glazes
and clay bodies.
Bill
-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG] On Behalf Of Lili
Krakowski
Sent: Tuesday, October 07, 2008 10:32 AM
To: CLAYART@LSV.CERAMICS.ORG
Subject: That iron chromate glaze
First I ran the glaze through Glaze Master (TM)., naming it
WhyBlue Glaze
.305 Na2O
.066 K2O
.003 MgO
.626 CaO
1.000 Total
.297 Al2O3
.371 B2O3
.002 Fe2O3
3.815 SiO2
.002 TiO2
I think, by the way, that the recipe could be simplified.
However. It is a calcium borate glaze, with soda as the primary
extra flux.
I have had several times blue glazes resulting from iron and
boron. I have a set of small bowls with a lovely blue glaze that
never even heard of cobalt. So my guess here is that the iron
chromate provided enough iron for that blue, that the chrome did
not "distract" from it--and that in other instances the copper
undid the blue and
made the whole thing green.
I would love to see the same glaze tested with just 2% or so of
iron.
If the underlying body contains iron- that would contribute to
the effect.
Lili Krakowski
Be of good courage
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