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matt crackle raku?

updated sat 30 nov 96


Jack Phillips on mon 28 oct 96

To the glaze wiz's,

I am trying to acheve a matt crackle effect on raku and am reaching
a high frustration level. In order to save on the supplies I wanted to ask
the list if anyone has had success in this area that they would be willing
to share. I have tried searching the ceramics-web but I still can't seem to
get that to properly search. I am useing a ^10 white sculpture clay. In the
glaze category
I need some fresh directions, so I haven't listed what has failed me so far.

Am I asking a glaze to do something it can't given the narrow band of
maturation? I either get a "dry effect" that won't crackle, (this is one
whole type of glazes) or a surface that has areas of matt and gloss, (
another whole type of glazes). I think alot of people could benefit from
this glaze. Anybody care to share?

Jack Phillips
STONART Ceramic art
Portland, Oregon

Web site:

Harvey Sadow on fri 15 nov 96

Jack Phillips wrote:
> ----------------------------Original message----------------------------
> To the glaze wiz's,
> I am trying to acheve a matt crackle effect on raku and am reaching
> a high frustration level.

Sorry to take so long to reply to this, but it just resurfaced
in my "answer this" file. Almost any surface will "crackle", if the
shock of cooling is intense enough and there is a disparity between the
surface and clay's coefficients of thermal expansion (and contraction).
All of my raku surfaces these days are so fussy and performance
specific that it is hard to generalize, but if you start with a base of
50% clay and add fluxes to it which promote desired color and textural
qualities, and then move up or down in either flux percentage or
temperature, or speed of firing, all of which are relevent to flow and
crackle, you can hit the matte crackle effect you want. Fire fast,
look for the sheen before the boil and the gloss. Don't be afraid of
being specific. I truly fire with a pyrometer, a barometer and a clock.
Raku is about spontaneous effects unless you develop techniques to
control it. Then it's about choreography.
Additionally, you can create very specific matt crackle effects
by using a hard surface frit based crackle glaze and a gentle touch with
a sandblaster at lower than normal pressure. If you use a super
abrasive compound and high pressure, you will rip the surface right off
the clay. Even then, I occasionally do just that to expose a crackle
pattern in the clay beneath the glaze. It takes just the right
combination of recklessness and finesse.
Have fun,
Harvey Sadow