Imzadi Donelli on sat 22 sep 01
<< One of the reasons I like terra sig so much is that when it is applied in
very thin coats to bone dry wares, it introduces enough moisture for good
polishing. Since the clay beneath is bone dry, all shrinkage has already
taken place. Apply terra sig (no thicker than 1.15 density) in multiple
coats until you build up the surface you want, let the surface moisture soak
in, and then polish with the grocery bag plastic stretched over your
fingertips. In my experience, the kind of polishing movements does not
matter much, as long as you cover the whole surface systematically. >>
Vince, I did this with three bone dry pots. But after I applied the third
coat, the terra sig started to peel off two of the pots. One pot, I
eventually had to scrape and sand off all the terra sig back down to the bare
clay. The other one, the terra sig is hanging on for dear life, until it gets
bisqued. just hoping it will stay on once it's bisqued. The first pot I terra
sigged is fine so far. Smooth and shiny, no peeling or cracking.
Any ideas what happened/and what to do about the other two pots? I'd hate to
not saggar the bare pot, but I'm afraid of terra sigging it again.
Imzadi
vince pitelka on sat 22 sep 01
> Vince, I did this with three bone dry pots. But after I applied the third
> coat, the terra sig started to peel off two of the pots. One pot, I
> eventually had to scrape and sand off all the terra sig back down to the
bare
> clay. The other one, the terra sig is hanging on for dear life, until it
gets
> bisqued. just hoping it will stay on once it's bisqued. The first pot I
terra
> sigged is fine so far. Smooth and shiny, no peeling or cracking.
Imzadi -
It sounds like your terra sig was mixed too thick, and therefore applied too
thick. Did you thin it to a density (specific gravity) of 1.15 or less? If
not, it is no wonder that your sig peeled. If you are applying very thin
layers, 1.15 or less density, then you should not have any problem. Terra
sig is of course the isolated fraction of extremely fine particles, and
therefore the shrinkage is extreme. With an extremely thin layer this is no
problem, but if the terra sig is applied any thicker, you can expect
problems. To get the finish I want, I usually apply eight or ten layers of
sig, and I never have any problems with chipping or peeling.
One other consideration is the degree to which you are smoothing the
exterior of the pot. If the surface is extremely smooth, and you apply a
lot of sig, you sometimes have problems with peeling or chipping. One
solution is to sand very lightly before applying the sig.
Good luck -
- Vince
Vince Pitelka
Appalachian Center for Crafts
Tennessee Technological University
1560 Craft Center Drive, Smithville TN 37166
Home - vpitelka@dtccom.net
615/597-5376
Work - wpitelka@tntech.edu
615/597-6801 ext. 111, fax 615/597-6803
http://www.craftcenter.tntech.edu/
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