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crazed glaze on porcelain - cone 8 oxidation

updated tue 11 dec 07


May Luk on mon 10 dec 07

Hello all;

I have a transparent clear glaze that works fine on my stoneware clay. (Standard 182 and Laguna B-mix) The glaze is very glossy and transparent. I am putting porcelain slip on the stoneware to make my 'poor man's porcelain' (Standard highfire Grolleg, but I forgot the number) The glaze crazed a bit on the bowl bottom where it's slightly thicker. The craze is a couple of curved lines of 1 - 2" long.

The recipe is as follow:

Glossy Transparent
Custer Feldspar - 59.4
Whiting --------- 17.4
Zinc Oxide ------ 5.1
OM4 Ballclay ---- 6.0
Silica ---------- 12.1

Na2O ----- 0.088
K20 ------ 0.193
MgO ------ 0.005
CaO ------ 0.525
ZnO ------ 0.189
Al2O3 ---- 0.350
Fe2O3 ---- 0.003
SiO2 ----- 2.825
TiO2 ----- 2.825
Si:Al ---- 2.825
COE ------ 80.87
LOI ------ 8.66

I would like to use this transparent glossy glaze for both my stoneware and porcelain. This is the first time I have to fix crazing. I am thinking of adding some calcium borate frit like 3134 and take out some silica (because of the added silica in the frit) to lower the expansion. Will this be a good strategy?

What would be the way if I want to take the clay slip alteration route?

Many thanks
Kings County