Develop a career as
a professional potter.

NIC’s ten-month Professional Potter Advanced
Diploma will help you develop innovative design
skills and production techniques along with
valuable business and marketing expertise.

Learn from world class instructors
~ Tony Clennell, Gordon
Hutchens, and Alan Burgess.

Enjoy access to fully
equipped studios with
a wide range of kilns,
including a rare Tozan-
style Anagama kiln.

Then, complete an
internship with a
professional potter
or at Medalta
International.

CRISTOBALITE

by Bruce Nyeste

We have recently experienced clay problems
with pots cracking (dunting) for no apparent
reason. So after some extensive research we
established the reason for our problems:

If you are using a white stoneware or
porcelain clay body and have started having
problems with dunting and pots breaking for
no apparent reason after they are fired, the
culprit may be CRISTOBALITE.

Cristobalite is a silica crystal structure that
forms in clay bodies that are fired above
1100°C and held for an extended period of
time. It is the result of silica being ground to
350 mesh or finer. The cristobalite changes
chemically from beta to alpha at 220°C which
causes a sudden 2-3% shrinkage and this is
the reason for the dunting and breakage
problems. Reheating in the oven or re-firing
may also cause dunting.

With new crushing methods of silica
a much higher volume is crushed to 400
mesh and finer which increases the chances
of cristobalite forming in clay bodies. The
addition of talc to a clay body also helps to
promote the cristobalite growth.

For more information and technical reasons,
check out  http://digitalfire.com/4sight/
glossary/glossary_cristobalite.html or
an amazing article by Peter Sohngen at
www.studiopotter.org/pdfs/sp28_1_
sohngen.pdf

PGBC member Bruce Nyeste of Mud Sweat
and Tears Pottery is situated in Blind Bay on the
shores of Shuswap Lake. They use stoneware and

Length: 10-month advanced diploma
Tuition: $9,180 approx / year
May 2014

porcelain, to produce functional, sculptural and
one of a kind pieces. Mud Sweat and Tears has
an annual contract to make 4000 - 5000, honey
pots for the Nicola Valley Apiary in Meritt. See

more at: ww.mudsweatandtears.ca

Starts:

Work by
Gordon
Hutchens

RITISH
COLUMBIA
a

Potters Guild of BC Newsletter - December/January 2013/14 9