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underglaze and raku firing - results

updated wed 21 jun 06


Carole Fox on tue 20 jun 06

I posted a question a couple of weeks ago re using underglazes under a
clear crackle glaze in raku firing. Got quite a range of responses, all
the way from "never worked for me" to " works fine, do it all the time",
to paraphrase a few. The question originated because I had seen some
posts in the archives indicating that some people had problems with the
colors fading or disappearing completely.

Well, this weekend I tried 3 different Amaco underglazes (Light Red,
Navajo Blue, and Turquoise)on two pots each. All three colors came
through just fine. I got pretty much the same shades as I have previously
gotten with ^6 electric firings. I brushed the underglazes on while the
pot was still pretty wet - just dried the surface of the pot lightly with
a heat gun so the underglaze would flow on smoothly. 3 coats of
underglaze, bisque fired on the pot before glazing. The clear crackle was
brushed onto the bisque ware. Fired until glaze was shiny, then reduced
in excelsior / wood shavings / paper for about 15 minutes. The glaze
crackled well; however, the areas over the underglaze did not pick up as
much carbon in the crackle lines as the areas without underglaze. I
suspect that the underglaze layer is not as open and absorbent as the clay
body, so can't take hold as much carbon.

I was pleased with the results - will probably use more underglazes in the
next firing.

Carole Fox
Dayton, OH