Snail Scott on wed 23 jun 04
At 08:37 PM 6/22/2004 -0700, Tammy wrote:
>...When I fire a piece that I have slowly fired to cone
>04 in bisqueing the second time, do I fire it as
>slowly as the first time ?
Nope. Bisque firings are generally slow because the
greenware is fragile, needs time for the water to
evaporate without turning to steam, and time for the
organics to burn out. If you re-fire to 'bisque'
temperatures, the clay is sintered, and the organics
are already gone. It may have re-absorbed some water
since the last firing (through glazing or humidity),
but since the clay is stronger now, you don't have to
be quite as cautious.
One proviso:
If the piece was fired the first time with a coating
that's now semi-vitrified (like an engobe) and then
re-wetted by glazing, water can be trapped under that
layer (like condensation in a broken headlight) and
cause steam to be trapped. If this is the case with
your piece, you will want to give it a long candling
to dry it out before beginning the real temperature
rise. Sitting around at room temperature is often not
sufficient to dry out moisture trapped under a
vitrified surface layer. (If the surface is a slip
made of the base clay only, I wouldn't worry.)
-Snail Scott
Edwardsville, Illinois, USA, Earth
tammy brown on wed 23 jun 04
Thank you Snail.
That makes sense to me. I made the slip from the clay
body with which I built from. I may fire it without a
glaze. I was hoping I did not have to fire it quite as
slowly, for goodness sake, it took pretty much the
better part of three days to fire by John Jensens'
firing sequence recommendation. It turned out just
beautfully! I am quite happy with it and it was well
worth the wait. I do have a firing sequence with my
Skutt for candling and I will use that if I decide to
glaze this piece. I was just unsure whether I should
even glaze considering the flaking thing. ]I really
think the bust might have been drier than usual when I
painted it, so that explains the flaking. I slip
covered the entire head with white. After the bisque I
simply well....kind of antiqued it with a wash, so I
may just fire it without a glaze.
I am intrigued by the thought of using crackle glazes
and rubbing them with india ink or permanent ink, but
it must be just the right piece to do this. I saw a
piece done like that and was overwhelmed.
That was quite helpful Snail, thank you.
Tammy
Clay Image Studio
--- Snail Scott wrote:
> At 08:37 PM 6/22/2004 -0700, Tammy wrote:
> >...When I fire a piece that I have slowly fired to
> cone
> >04 in bisqueing the second time, do I fire it as
> >slowly as the first time ?
>
>
> Nope. Bisque firings are generally slow because the
> greenware is fragile, needs time for the water to
> evaporate without turning to steam, and time for the
> organics to burn out. If you re-fire to 'bisque'
> temperatures, the clay is sintered, and the organics
> are already gone. It may have re-absorbed some water
> since the last firing (through glazing or humidity),
> but since the clay is stronger now, you don't have
> to
> be quite as cautious.
>
> One proviso:
> If the piece was fired the first time with a coating
> that's now semi-vitrified (like an engobe) and then
> re-wetted by glazing, water can be trapped under
> that
> layer (like condensation in a broken headlight) and
> cause steam to be trapped. If this is the case with
> your piece, you will want to give it a long candling
> to dry it out before beginning the real temperature
> rise. Sitting around at room temperature is often
> not
> sufficient to dry out moisture trapped under a
> vitrified surface layer. (If the surface is a slip
> made of the base clay only, I wouldn't worry.)
>
> -Snail Scott
> Edwardsville, Illinois, USA, Earth
>
>
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