search  current discussion  categories  techniques - misc 

question on burnished pots

updated sat 18 sep 99

 

Valerie Mann on tue 14 sep 99

When you burnish and it gets shiny....won't that cause a "hard spot"
so any glaze you put on it won't take?....or am I way off on
this....I know that is what happens when you pour molds and then if
you rub too hard in a spot it becomes a hard spot!!!!
This is all new to me so I just thought I would venture forth and
'ask'....LOL

Nina Jones on thu 16 sep 99

Hi, Valerie:

Yes, you are creating a "hard spot" or "hot spot" but in the case of
a burnished pot, that is exactly what you want to do. Burnished pots
are not glazed. You are trying to water seal the pot as they did in
primitive times, thus the name for the type of firing that is
sometimes done for burnished pots "primitive firing" (referring to pit
firing.) Of course you can fire burnished pots in an electric, gas
and wood burning kiln as well, though in an electric kiln you can't
reduce to get the beautiful blackened pot effect (;~`). If done
properly, and not overfired (should usually fire between ^08 and
^06--though I guess that might depend on the clay ??--so that you do
not burn out the shine), you will get a beautiful, shiny,
silky-surfaced pot without using a clear glaze.

Nina D. Jones
Southside Chicago
@ njones@winston.com

>>> Valerie Mann 09/14/99 03:28PM >>>
----------------------------Original
message----------------------------
When you burnish and it gets shiny....won't that cause a "hard spot"
so any glaze you put on it won't take?....or am I way off on
this....I know that is what happens when you pour molds and then if
you rub too hard in a spot it becomes a hard spot!!!!
This is all new to me so I just thought I would venture forth and
'ask'....LOL

Martin Howard on fri 17 sep 99

Nina wrote:-
and wood burning kiln as well, though in an electric kiln you can't
reduce to get the beautiful blackened pot effect (;~`).>

I have just bought some silicon carbide with the intention of doing some
localised reduction firing in my electric kiln at cone 02-1 I haven't
done it yet, so any help will be much appreciated from those who have.

I read from page 69 of Glazes for the craft potter (by Harry Fraser)
that "When glazes are loaded with silicon carbide and fired, the silicon
carbide oxidises preferentially. If the firing cycle is correct and the
right amount of silicon carbide is present, then metallic oxides present
in the glaze will be reduced. ... A good starting range for experiments
would be up to 5 per cent addition of copper or iron oxide and 3-8 per
cent of silicon carbide as necessary."

It almost sounds as if even Harry has not done it ... yet :-)

Could we actually use a terra sigillata, (my finest cat litter for
example), burnish it, add somehow copper oxide and silicon carbide, and
arrive at a gorgeous burnished copper red?

Just where in the process does one add the copper and the carbide?

Martin Howard, probably dreaming as an alternative to some never ending
experimentation.
araneajo@gn.apc.org