Jo Gilder on wed 15 apr 98
I have a few questions about burnishing and slip painting. It is a new
technique for me and I am getting mixed messages. Here goes:
Do I burnish first, paint with slip, and then burnish again or
do I just paint with slip and then burnish?
Is it necessary to burnish after the slip has been painted on?
What happens if you don't, does it just flake off?
Is this process known as terra sigilata (sp?)?
Thanks,
Jo
--
Jo Gilder
Panama City, FL
Dannon Rhudy on thu 16 apr 98
Jo,
... Do I burnish first, paint with slip, and then burnish
again or do I just paint with slip and then burnish?....
You apply slip first, and then polish with a soft cloth. But it
should be a slip specifically meant for that purpose (i.e., terra
sigilata). There are various ways to make this slip, requiring
more or less attention/trouble. The more trouble you take, the
better the terra sigilata.
..... Is it necessary to burnish after the slip has been painted
on?......
No, it is not NECESSARY, but for certain firing techniques, it is
the REASON for the terra sigilata. It doesn't really require
burnishing, so much as just a quick polishing with a soft cloth.
..... What happens if you don't, does it just flake off?...
No, flaking off is a problem related to other issues, shrinkage
of clay versus shrinkage of slip, etc. The polishing is to give
a glaze-like surface without glaze, and help seal the surface.
This a low-fire technique, by the way. You did not say if you
plan to pit fire or saggar fire the work. If your plan is to use
the slip decoratively for high(er) fired wares, then that is
another subject entirely.
... Is this process known as terra sigilata (sp?)?.....
Terra Sigilata is not a process, but a substance; a fine slip
meant (originally) for coating wares to decrease permeability at
relatively low firing temperatures. It also can make them
wonderful to both eye and hand - serendipity is a fine thing.
If you look in the archives, you'll find a recipe for a super-
refined terra sigilata (courtesy Vince Pitelka). And no doubt
other terra sigs, too.
Dannon Rhudy
potter@koyote.com
Thanks,
Jo
--
Jo Gilder
Panama City, FL
Azclockdoc on thu 16 apr 98
In a message dated 4/15/98 7:50:25 AM EST, magilder@worldnet.att.net writes:
<< Do I burnish first, paint with slip, and then burnish again or
do I just paint with slip and then burnish? >>
Do not burnish before you apply the slip. The slip will adhere much better to
the unburnished (rough) surface. Applying slip to a burnished (smooth)
surface will greatly increase the chances of it flaking off.
<< Is it necessary to burnish after the slip has been painted on?
What happens if you don't, does it just flake off? >>
It is not necessary to burnish after the slip has been painted on. If you
don't burnish, the slip will have a soft, matte finish rather than a shiny,
burnished finish. The slip will not flake off just because it is not
burnished. Prehistoric, native american pottery was often slipped (especially
white and red pottery) but never burnished. They only started doing that in
historic times because white people liked shiny things.
<< Is this process known as terra sigilata (sp?)? >>
If you simply dissolve clay in water, let the heavier particles settle out and
pour off the top layer of finer particles, you have slip. Since I only teach
Traditional Native American pottery, I only use the plain old "slip" .
However it is my understanding from past postings on this list that if you get
more scientific and add a deflocculent to your suspended clay solution to keep
the finer particles in solution longer, then you have terra sigilata (sp?).
This may be an oversimplification of what Terra sig is, but if it is I am sure
there are more qualified people on the list who will correct me.
John Guerin
Tucson, AZ
Vince Pitelka on sun 19 apr 98
Jo -
You can find my whole spiel on terra sig on Tony Hansen's website at
http://digitalfire.com/education/glaze/terasig.htm
With a properly prepared terra sig, the platelates (disk-shaped clay
particles) are so small that they naturally tend to lay flat on the surface,
and create a dull sheen all by themselves. While still damp (when applied
to a bone-dry surface) the terra sig can be polished to a dull shine with a
soft cloth, or to a high shine with a piece of grocery store bag plastic
stretched over the finger tip. When polished in either of these ways, the
sig will still show the irregularities of the clay surface, although this
depends on how many layers of sig you build up. It should be applied VERY
thin, and built up in successive layers. You need not polish it until you
have applied the last layer. But if you polish it and think it needs more
sig, that will work fine with no increase in problems with peeling and
flaking (this is not true with burnishing).
Terra sig also makes an excellent burnishing slip, in case you want to use
stone burnishing to get the smoothest, shiniest, densest surface. When
burnishing, you should never start burnishing until you have applied the
final coat of sig or slip. When you finish burishing, if you decide the
surface is inadequate, and want to start all over, you must disrupt the
surface by sanding, or by scrubing lightly with a sponge. When burnishing a
small form, you may be able to complete the burnishing process with only the
moisture introduced by the slip. When bunishing a larger surface, after you
have applied your sig or refined slip, you can apply a light skim coat of
lard, vegetable oil, or glycerin, and then burnish. Do not be concerned by
the fact that initially you just seem to be smearing the surface. You are
compacting and smoothing the surface. Stick with it and be amazed.
Remember also that a true burnished surface cannot be fired any higher than
around cone 018 - 014, or you will loose the burnishing as the form begins
to shrink and the surface buckles on a microscopic level.
Good luck -
- Vince
Vince Pitelka - vpitelka@DeKalb.net
Home 615/597-5376, work 615/597-6801, fax 615/597-6803
Appalachian Center for Crafts
Tennessee Technological University
1560 Craft Center Drive, Smithville TN 37166
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