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what would cause this? glaze/underglaze interaction

updated tue 6 nov 07


Leigh Whitaker on mon 5 nov 07

I'll try this question again...

I am trying to find a clear glaze to go over Speedball underglaze black.

I normally use Amaco Sahara HF-9 (which is a zinc free glaze) over Amaco
velvet underglazes. I bought some Speedball underglazes to try out since I
found them on a good sale. The Speedball products recommend use of their own
clear glaze over the top, but I figured that since the HF-9 was zinc free, and
the Speedball black underglaze was probably using a Mason or Mason-like stain
for the pigment (and the all Mason stain blacks recommend a zinc free glaze)
that the HF-9 would probably work.

However, this glaze/underglaze combination was not good. I got a very
textured and pinholed surface. [Although the HF-9 worked fine over all the other
Speedball colors (red, blue, green, yellow, white, violet)].

I've got two other clear glazes to try out, but I was hoping that someone
could give me an idea of what the problem might be. What sorts of interactions
might cause something like that? It might save me some time in testing.
I'll buy the Speedball brand clear glaze if I have to, I was just hoping to
make my own.


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