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pitfire clays: results and questions

updated fri 12 apr 02


Lori Leary on thu 11 apr 02


For pit firing, I have adopted a recipe of Vince's that calls for:

25% ball clay
25% fire clay
25% goldart
25% fine grog

I use terra sig, so I bisque between 018 and 010. I have hosted two of
Vince's workshops using this clay as well as for my own work and have had
excellent results. If you use commercial clay, just make sure you have LOTS
of grog.

I would love to hear how the 04 glaze lining works, never have done that. I
know that Bennet Bean uses some sort of lowfire glaze for his work. Also,
does the higher bisque temp affect the color on the sigged surfaces?

Hope this helps ,
Lori L.
Mountaintop, PA

> I'm still getting lots of pots with cracks in them when I pit fire. I've
> tried the following with noted results. Pieces were polished terra sig
> bisque fired to either 018 or 04. When ^04 I lined with commercial ^04
> clear glaze. pit was 3' x 3' cement block above ground.
> Laguna eastern 10T - Works great on mini to medium size pieces. Seems to
> encourage orange flashes when using copper sulfate. Not good for large
> pieces
> Laguna eastern #55 - unfavorable results all around
> Laguna eastern #45 - unfavorable
> Standard #112 - ok results still seeing cracking in large pieces
> Standard Raku - I was surprised but lots of cracked pots - these were
> however.
> Standard #153 - Very nice results but still a low % of cracking
> Laguna eastern #200 raku - this is the heavier grogged raku clay. tough
> the hands when throwing. Will be pit fired tomorrow.
> Can anyone see why I might have such a high breakage rate? I am beginning
> to notice if I have a real ragin' fire I get more cracks but I'm still
> surprised at how many crack. When I did Bob Compton's workshop, none of
> pots cracked and we had one impressive fire ragin' through the night!! I
> can't figure why the difference. I am wondering if some forms lend
> themselves to breakage more than others.
> Any help appreciated,
> Kim