TETKOWSKI@AOL.COM on fri 15 sep 00
Some additional thoughts here for people struggling with proper terra=20
sigilatta application. As Jonathan Kaplan notes in his recent CM technical=20
comment, chipping and flaking are common and frustrating for many people=20
working with terra sigilattas. There are a combination of precautions I=20
suggest that are best used together to ensure the best permanent application=
..=20
You can get beautiful results. Let=92s see how.
The consistency of the liquid terra sigilatta is crucial. Too thin or too=20
thick will cause problems after the firing. I like a consistency thicker tha=
n=20
cream and thinner than house paint. Your goal is to apply as thin a coating=20
as possible and still cover your clay body. I=92ve never seen chipping or=20
flaking when the application is very thin. But if the terra sigilatta=20
consistency is too watery or milky to begin with, you will not get the prope=
r=20
bond. By the time you have covered the clay body, chipping and flaking will=20
be inevitable.
Prepare the surface of your dry ware with a green scrubby pad and you will=20
further minimize application problems. There is a simple reason for this.=20
Most earthenware bodies have natural soluble salts, which accumulate on the=20
edges and surfaces during drying. When enough soluble salts are present you=20
will see scumming after the firing. Scumming is the chalky surface that will=
=20
not wash off of some fired earthenware. The important thing to consider is=20
that the soluble salts may get between the clay body and your terra sigilatt=
a=20
ruining your application. So it is best to gently prep the surface of your=20
dry unfired work before you apply the terra sigilatta.
The Fifth Century BC Greek potters were masters of terra sigillata and their=
=20
work is an inspiration to anyone who loves this process. How did they do it?=
=20
The Greeks used a wood fired kiln to produce the beautiful well-known red an=
d=20
black figure ware. It is only with a firing cycle of repeated oxidation and=20
reduction that such colors and surfaces are possible. When they got=20
everything right it, the results were and still are remarkable. The Greeks=20
painted the terra sigilatta on leather hard ware. Sometimes they also got=20
chipping and flaking when their application went on too thick. You can see=20
the defects for yourself if you look closely at Greek pots, in even the best=
=20
museum collection.=20
Terra sigilattas can be successfully dipped poured or painted on the ware. I=
f=20
you control the variables you can make it work. However, I prefer spraying=20
the liquid terra sigillata on dry work for the greatest control of the=20
application and to enhance the overlap of various colors together.=20
Neil Tetkowski
NYC
vince pitelka on fri 15 sep 00
> The consistency of the liquid terra sigilatta is crucial. Too thin or too
> thick will cause problems after the firing. I like a consistency thicker
than
> cream and thinner than house paint. Your goal is to apply as thin a
coating
> as possible and still cover your clay body.
Neil -
This is misleading. In my experience, thicker than cream is way too thick
for terra sig. We should not expect the terra sig to cover in one
application. There is no such thing as terra sig which is too thin, and I
have never encountered any bonding problem with thin terra sig. It does not
give an opaque covering, but a semi-transparent coat of terra sig can be
very appealing. I like an opaque coating,and I generally apply six to ten
coats of very thin (1.15 s.g.). It shines beautifully, and I never have any
problems with chipping or flaking.
> chipping and flaking when their application went on too thick. You can see
> the defects for yourself if you look closely at Greek pots, in even the
best
> museum collection.
It is always interesting to view the Greek pots that did not turn out well
due to technical flaws. The only chipping and flaking I have experienced in
my own terra sigs was on over-reduced wares with a redart terra sig. No
surprise there. Makes it easy to understand how the Greek red-black
technique was so precarious. They used draw-tiles to determine when the
fluxed black terra sig had vitrified, locking in the black ferrous iron
oxide, while the un-fluxed red would re-oxidize to ferric iron.
Best wishes -
- Vince
Vince Pitelka
Home - vpitelka@dekalb.net
615/597-5376
Work - wpitelka@tntech.edu
615/597-6801 ext. 111, fax 615/597-6803
Appalachian Center for Crafts
Tennessee Technological University
1560 Craft Center Drive, Smithville TN 37166
http://www.craftcenter.tntech.edu/
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