search  current discussion  categories  techniques - cracking 

spiral cracking

updated thu 9 may 02

 

Al Tillis on wed 8 may 02


While throwing some bottles using a 50/50 porcelain/stoneware I have
had some spiral cracking up the sides sometimes after the bisque
and some have bisqued just fine but do it when fired for the glazing.

It is more than a crack as I can almost stick a piece of paper in the
'crack/break'
It looks almost like some has carefully and accurately cut through the wall
with
a Dremel tool of sorts. The spiral goes from bottom to top in about one and
a half
revolutions, it almost looks like a spring since the entire wall is
penetrated.
It does not follow my finger grooves as they are more like 15 to 20
revolutions from bottom to top.

The bottle still has considerable strength about it. Some people like the
way it looks but it
is frustrating me just a tad.

My guess is this is something that happens to rookies and the answer will
be easy ....
I think maybe I need to pay special attention to compressing the walls more
often.....

Lay it on me...

Thanks in advance,
Al Tillis

If I knew how to control it that would be cool but it just pops up and
surprises me .... not cool.

Tommy Humphries on wed 8 may 02


----- Original Message -----
From: "Al Tillis"
To:
Sent: Wednesday, May 08, 2002 11:08 AM
Subject: Spiral cracking


> While throwing some bottles using a 50/50 porcelain/stoneware I have
> had some spiral cracking up the sides sometimes after the bisque
> and some have bisqued just fine but do it when fired for the glazing.


You are saying that you are using a mix of stoneware and porcelain...just
wedged together?

If so you need a more thorough wedging. What's that? you want the streaks
to show? well you need clays that have a more similar shrinkage rate. I
would suggest using one clay or the other, and using stains to color the
clays to show the spirals.

Tommy