Craig Martell on tue 1 jan 02
Hi:
It's always something!! You want blue, you get black. You want black, you
get green. :>) You want a serious answer and you get a sideways smiley face!
The cobalt colorant is contained in a slip which is a higher alumina
media. This doesn't allow the cobalt to be taken into solution in the salt
glaze too easily. I'm sure you are seeing a lighter more transparent blue
around the edges of your slip lines. Smaller amounts of cobalt are
diffusing into the body/salt glaze and this lighter concentration will
yield lighter blue tones.
B-mix isn't real white either so this will have an effect. You might try a
whiter porcelain slip. You can also decrease the kaolin and other clays
and add more feldspar and silica to make the slip more active. I don't
know what the silica/alumina ratio of B-Mix is but clays and slips that are
more reactive with salt and soda have a ratio at, or above, 5 to 1. The
higher the proportion of silica to alumina the more reactive the clay or
slip will be to salt and soda. A more reactive slip will give better
results with any colorant.
regards, Craig Martell in Oregon
| |
|
