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having trouble with commercial glazes over underglazes - very =

updated fri 18 sep 09


Snail Scott on wed 9 sep 09


On Sep 9, 2009, at 9:36 AM, Debbie Penley wrote:
> ...I am using Spectrum underglazes and one
> of their clear glazes, low fire...
> What's happening is that the glaze is not sticking to the entire
> piece. It's patchy,
> especially on blues and greens...

Are you firing the underglaze before applying the
glaze? A dusty unfired coating of underglaze
can cause adhesion problems, and some
formulations are dustier than others. If you
aren't currently firing the underglaze before glazing,
give that a try. You don't have to go all the way to
maturity; just hot enough to sinter it (^010-^012 or so).


Eleanora Eden on thu 17 sep 09


I concur with other writers; I fire all underglazes to ^04 before firing to=
with the glaze firing. I use 3-4 coats of underglaze. Haven't tried Spect=
I use mostly Amaco Velvets and Duncan Cover Coats, some Duncan EZ strokes.

If I need to make any corrections with the underglaze, I actually do a 2nd =
firing rather than put glaze directly over any unfired underglaze.

So my underglaze pots are getting a 1450F firing, then the underglaze work,=
another 1450F firing over corrections, then a ^04 firing, then the glaze fi=
ring. Seems
like a lot of firings, yes it is. But using underglazes in many coats is p=
the envelope quite a bit and the extra firings makes it work for me.


>I am feeling very frustrated right now. I am using Spectrum underglazes an=
d one
>of their clear glazes, low fire. At first I thought it was just their glaz=
es, but I
>looked back at some pieces I had made with Amaco's underglazes and glaze, =
>found the same problem, though not as pronounced.
>What's happening is that the glaze is not sticking to the entire piece. It=
's patchy,
>especially on blues and greens, though all the colors have the problem to =
>I made sure not to get oil from my hands on any of the pieces. The undergl=
>took very well. I wrote Spectrum and they suggested I was layering the col=
or on
>too thick, as well as the glaze, which I know I put on too thick one time.
>So this time, some of the underglazes are thin enough that you can see bru=
>strokes and see to the bare clay. I put one coat of glaze on, vs. two this=
>But the pieces still came out with patchy glaze. Some are so bad it's just
>unacceptable. But I'm not sure how to fix it...
>What in the world could I be doing wrong?

Bellows Falls Vermont