Vince Pitelka on fri 6 aug 04
This discussion really underscores the reality that terra sig is not easy.
It can be a very finnicky and tempermental material until you get the hang
of it. Comments by Wally and others show the kind of variable results you
can get in different firing processes. This is one of the reasons I spent
so much time researching terra sig with students Rob Thompson and Heather
Shadron at U-Mass. With this approach, the mixing, settling, and decanting
of the terra sig is standardized so that at least you can eliminate most of
the variables from the preparation process. There are still many variables
in the kind of clay you use, the surface on which you apply the sig, the
density fo the sig when applied, the kind of brush you use, the way you
apply the sig, the number of coats you apply, the polishing or burnishing
process, and the firing process. You begin to get the picture. Getting
control of all those variables is a matter of extensive experimentation and
practice over time, and it is never easy.
For those interested, my terra sig process is explained at the Digitalfire
website at http://www.digitalfire.ab.ca/cermat/education/274.html
In my "Ancient Clay" workshops we do a blackware bonfiring of polished terra
sig wares. We rarely have any problem with the sig flaking off, but we use
the terra sig I have prepared, and we sand all the wares before applying the
terra sig. The sig is applied in multiple coats of 1.15 S.G. consistency.
In this workshop I use only terra sigs made from Redart clay and from OM4
ball clay. In the past we burnished some of the wares, but we get such a
good shine from polishing the sig with grocery bag plastic, and we rarely
burnish any more. Burnish does give a very special surface and appearance,
but in a three to five-day workshop it becomes a matter of making the most
of the available time.
Best wishes -