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crackle techniques

updated tue 31 dec 96


Tadeusz Westawic on mon 30 dec 96

Stern HQ wrote:
> ----------------------------Original message----------------------------
> I have another question about bathroom sinks. I have been asked to make
> one for a friend who wants a crackle finish. I told her I thought that
> would allow water to escape and besides I thought the sink should be
> stoneware which, when vitrified, wouldn't allow water to seep. Any
> thought on either subject? Thanks in advance and Happy Holidays to all.
> Jeni Stern

These suggestions are probably not what you are looking for, but I
wanted to add what I do to the "crackle" thread. Anyway, I'd like to
know if/share with others doing similar stuff.

I raku exclusively, and there are two tricks I use that may help you get
a crackle appearance on an uncrackled glaze. These are new techniques
for me and I don't claim any mastery.


1. I coat my bisque pot with several layers of slip.
2. When the slip is leather or drier I fire the pot at low heat until
the slip developes shrink cracks, like the mud at the bottom of an
evaporating puddle. The thicker the slip, the coarser the "texture" of
the crackling. All too oftern, the slip falls off the pot in the "wrong"
way, but often enough it works okay.
3. With the pot out of the kiln, I force spray a patina or oxide stain
onto the pot using the crackled slip as a mask. I use a cheap pitot or
siphon type airbrush for this and concentrate spray into the cracks, but
I don't let it run (a hot pot helps prevent the runs also).
4. Carefully knock-off the slip. If it sticks to the pot I use a
propane torch and safety glasses to "pop" it off. If I have
accidentally fully bisqued the slip, then a miniscule amount of water
spray just before propane application will loosen it from the pot.
5. Now an overall clear glaze coat and fire to finish.

Okay, I've never done a sink. And I can't tell you how to develop a
proper slip for this technique. But I figure maybe you know something
yourself or maybe you'll get lucky. So for what its worth, there it is.

SECOND TECHNIQUE: Alligator Finish (this was a happy accident and I've
only done it once)

I glaze fired a pot using a glaze I knew would crackle in the cooling
(this is cooling in the kiln, not a raku firing). It was a glassy,
emerald green copper glaze(^06), and I wanted to turn the crackle
pattern gold by rubbing some rutile into the cracks and then refire it.
So, when the pot was cool I rubbed on the rutile and then wiped it off,
figuring the rutile in the cracks would not wipe off. I started the
second firing. After a while I lifted the lid to the kiln to see how
things were progressing, and there was this alligator-skin pot. So I
called it "done" right there, at about dull red temperature.

I figure the rutile both fluxed and expanded in the cracks. Also first
melting of anything solid begins at crystal boundaries. Here it began at
the edges of the glass islands that the crackle creates, and caused them
to expand, and I caught it just at the right time. Maybe one of the real
techs in the list will comment.

Hope this inspires comments.