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controlling glaze crackle mesh size/island size

updated thu 22 jul 99


Bruce Girrell on wed 21 jul 99

What factors control the size of the crackle mesh (or the uncracked islands)
of a crackle glaze? In particular, what things tend to make the mesh more
open or the islands larger?

For reference, see "Raku Globes" by Suzanne C. Koglin and "Untitled" by
Gladys Soued in the Gallery section (pp. 40-41) of the most recent
(June/July?) issue of Clay Times or "Large Bulbous Raku Pot" by David
Roberts (p 51) and "Raku Hare" by Jennie Hale (p 126) in _Raku A Review of
Contemporary Work_ by Tim Andrews. Jennie, if you're out there, I love that

Each of these examples has what I would consider mammoth-sized islands
within the primary crackle network. Some smaller cracking is visible, but it
is very much subdued compared to the primary network.

I tried creating a glaze with a very large COE. That doesn't work. LOTS of
cracks, but tiny mesh size. Lowering the COE helped, but my average island
size is about 1/4 inch or 1/2 cm.

I tried applying the glaze thicker, thinking that the glaze would be more
cohesive. Doesn't seem to do anything. Applying the glaze too thinly
eliminates cracks.

I tried spraying with water. This gave me localized patches of fine cracks.
Nice, but not exactly what I was after.

I've tried 80/20 GB/NS glaze and other variations. I've done an Ian Currie
style test (with 100% frit 3110 in corner C) and got a pretty good glaze at
position 28, but still the island size averages about 1/4". I thought maybe
I would see increasing island size with increasing kaolin, but that doesn't
seem to be a major factor.

So what am I missing? Any suggestions? I really want to avoid high gerstley
borate recipes because of the bubbling.


Bruce "cracking up" Girrell