Lili Krakowski on tue 14 mar 06
Robert Cope writes:
" I am currently using Hopper slip (Ball clay 75% Kaolin 10% Silica,10%
Feldspar 5%) at Cone 6 ...In use, the slipped part will absorb oils
(although coffee or tea stains wash out). "
No one can have a recipe that works for everyone every time.
But let me explain something about slips. They are clay in liquid
solution. Many times we use the clay body we are using to make a slip for
decoration. If you want a black slip, for instance, and are using a
satisfactory clay body, you can slack the body in a lot of water, screen it
to eliminate grog and/or sand, and then add colorants to make it black.
And one might consider buying a white clay body (at one's working temp) and
using that as a base for slip.
Having said that (I do love that expression, which often represents three
hours of babbling)
I think your slip is undefired. That it is almost there (coffee and tea
wash out) but oils soak in.
This brings up two questions. Is your clay body itself vitirifed enough?
Because all too often (as "tests" on stuff bought at craft fairs etc. show)
the clay body itself is not fired to maturity, but stains are not noticeable
because the body is fairly dark.
If an absorption test on the body shows it is ok, you need to adjust the
slip. Now the basic common white slip goes like this:
Ball Clay: 40-60 parts; Kaolin: 60-40 parts (inverse ratio to ball clay).
Add to that Feldspar : up to 20 parts; Flint: up to 20 parts; Zirconium
opacifier up to 5 parts; Borax 5 parts.
You may even want some Bentonite, for specific cases.
So. Suggestion: check that your clay body itself is mature. You shouold be
sure of that slip or no slip.
Then make some tests upping the feldspar content of your slip. I would do
it 5% at a time. As your slip "matures" you may want to add some zirconium
And here is another slip recipe you may want to try.
Ferro Frit 3124 14
Nepheline Syenite 14
Ball Clay 24
Note how much more flux there is than in your recipe..
Be of good courage