Tom Buck on sat 6 sep 97
Ok, Peggy: Here is one possible (underline ONE possible) answer to your
question about colour loss using a BurgUndy stain. The chemistry makes
sense but I am uncertain about the crystallography. If I err here I expect
others to clarify this aspect.
1) You are using the same clear glaze base both before and now, and it
is put on a bit thin (I guess) so not to become cloudy.
2) The burgUndy stain is a complex mix of metals, eg, in Tuckers list is
this for Lavender Cr Sn Co Si Zn ... these are NOT a mix of oxides but an
"alloy" in one sense, and the colour comes from the precise crystal matrix
of the "alloy" ... the alloy receives a ray of white light, absorbs one or
more wavelengths and then re-emits the rest, giving you the colour as
reflected light.
3) In a reducing atmosphere, one cannot reduce metals any further, they
are already at their lowest reduction level (zero valence). So unless you
overfire greatly to destroy the finely developed alloy, you will not
change the colour the stain yields.
4) Such is not the case in a firing where neutral or oxidizing
conditions prevail. Then, some of the stain's metals may be changed
into oxides, and it would not take much oxidation to alter the surface
atoms of the stain's crystal matrix, and hence goodbye expected colour.
If, for example, Tin (Sn) and Zinc (Zn) were the main metals present, they
would show the characteristic white of the oxides.
So why do not more stains suffer colour loss when fired in
oxidation? Most stain crystals are encapsulated, ie, coated with a clear
glaze (hence prefired in a special way, making them expensive). This
surface coat will protect the stain crystal from the kiln atmosphere as
long this glaze is below its melting point. But once beyond this
melting temperature, the colour becomes fugitive.
Tom Buck ) Hamilton,
Ontario, Canada
Karen Gringhuis on mon 8 sep 97
Peggy - I missed your orig qn. but "funny you should mention this."
New to Mason stains, I just ran some tests w/ #6005 crimson
(goal = an almost fuschia hue). Base 1 turned out WHITE, Base 2
a very very pale pink, Base 3 (MgO) a very pale lavender and
Bases 4 & 5 were crimson. Dumb founding. And dumb me. Going
back to the Mason stain folder virtually ALL of their reds &
also the purples have a footnote of #9 (?) stating that the
glaze must contain X% calcium. I blythly ignored this -
and voila, white. (THese colors are rated up to 2300F so it should not have bee
My stuido mate uses a lot of stains & has been getting blue instead of
purple. (Purple minus red = blue) But in one base, she just nailed
purple. And it is a base w/ 25% whiting/Ca and no dolomite/MgO.
Lesson to all - don't blow off those footnotes!
Next I plan to slip tests of the surviving bases (maybe even
the white ones, Tom?) into a redtn. firing to gather more
data.
Regards, Karen Gringhuis
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