Nancy Udell on mon 6 nov 06
> From: Nancy Udell
> Date: November 6, 2006 3:14:26 PM MST
> To: firstname.lastname@example.org
> Subject: Cone 6 Glazes -- Firing Schedule
> I have a problem I hope the glaze gurus might be able to help
> with. I'm firing cone 6 electric. The problem involves Ron and
> John's Glossy Base 1 with 2% Cob, .5 RIO and 5% Rutile.
> Base Glaze
> G200 20
> 3134 20
> Woll 10
> Kaolin 20 (using grolleg)
> Talc 11.5
> Silica 18.5
> The glaze is absolutely beautiful milky deep and bright blue if I
> put my kiln on Cone 6 and run the "fast fire" mode with a 20 min
> soak at the top.
> But if I have pots with this glaze in the kiln in which I am also
> firing my iron red, and I do a slow cool (150 F per hour down to
> 1500F) it turns ugly dark blue/brown, particularly on the top half
> of large forms. It doesn't run off the pot, but appears to run
> down and somehow thin out at the top. Bottom half doesn't look so
> great either, but marginally better.
> See two examples here: (I noted the exact firing schedules next to
> the pics) Firing schedule is the ONLY difference between the two
> -- amazing.
> I know I could fire this glaze separately, but aside from not
> wanting to fill a whole kiln with it I want to use the glaze on
> large patters (21") and large bowls (16"). I'm afraid to fire
> these on fast fire mode because of cracking.
> So, any ideas? Should I fire UP slowly thru quartz inversion and
> then soak and shut off at the top (no slow cool)? I understood
> that firing down thru quartz inversion was as important as firing up.
> Thoughts much appreciated.
> Nancy Udell
> Santa Fe, NM