joan woodward on thu 2 jan 03
More thanks to Ron and John for further responses to my initial inquiries. One more clarification, and then, sigh, still more questions.
Re: majolica: I prefer EZ Strokes because I already have them - probably 30 of them - and I really do paint detailed picturse on large platters. But I hear you, Ron, and may have to continue using the EZ's as underglazes rather than on top of glazes. And investigate mixing some stains in a clear for use more abstractly over majolica.
My main questions continue re. firing schedules. I got the one I originally posted (and use) prmarily from one of the folks at Clay Art Center, then modified the cooling per R & J's book. The schedule Alisa posted keeps a steady 330F f rom 112F to 2228F. I was told to keep it at 200F to 250F, and go slow (180F) between 1000F and 1150F and even slower (108F) from 1894F to my high temperature. On the cooling end, I understand what John is saying. It appears that slow cooling doesn't have to go all the way to 1100F as I was doing, but only to 1500F.
So . . . since I'm just beginning to learn the whys and wherefores of all this, I can't evaluate for myself whether to ditch my slower ramps on the way up. Seems like if it works for Alisa, it should work for me, but I'd appreciate any comments. I'd certainly love to shorten my firing schedule which now takes about 15 hours during which I'm tethered to the studio!
Thanks for listening to me one more time! Hope everyone's having as nice a start to the new year as I am: kiln's loaded and my daughter's here for a visit. Picture talking and eating, hiking and talking, eating and talking, shopping and talking, skiing and talking, eating and talking. . . .you get the idea.
Joan
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John Hesselberth on thu 2 jan 03
Hi Joan,
You will probably get lots of opinions on this. I'm not sure there is
much hard data (except it works for me) to support any particular glaze
firing schedule except near peak temperature and, in some cases, when
you go through transition temperatures-see the next paragraph. I
personally go pretty fast--about like Alisa does-- until I reach 100-150
deg F from peak. Then I slow down to 100/hour (actually i use 108 for no
good reason except that is the rate of rise Orton uses on one of their
temperature charts). Then I soak 15-20 minutes, drop quickly to 1900 and
slow cool down to 1500.
I think you have probably been told to go up slowly based on people's
experience with big, massive pots. When you go through the transition
temperature of 573C (1063F) where the silica changes from alpha to beta
form and expands rather suddenly it is best to be going slow enough to
make sure the inside and outside of the clay expand at the same time.
For small, thin pots this is not a big issue. For big, thick ones it can
be. There is a bigger concern on the way down at 226C if you have a
significant amount of cristobalite in your body. We don't have to worry
much about that at cone 6.
Regards,
John
On Thursday, January 2, 2003, at 11:38 AM, joan woodward wrote:
> So . . . since I'm just beginning to learn the whys and wherefores of
> all this, I can't evaluate for myself whether to ditch my slower ramps
> on the way up. Seems like if it works for Alisa, it should work for
> me, but I'd appreciate any comments. I'd certainly love to shorten my
> firing schedule which now takes about 15 hours during which I'm
> tethered to the studio!
http://www.frogpondpottery.com
http://www.masteringglazes.com
Ron Roy on mon 6 jan 03
Hi Joan,
While I have no experience with this type of Glaze it may be possible to
cure the problem by adding clay to them.
Take a measured amount and stir in (sieving would be better) a little clay
- kaolin would be fine In 100 grams of dry EZ add 2 grams of EPK - put a
brush stroke of this on a tile - then add 2 grams more of clay, repeat till
you have added a total of 10 grams - fire the tile and see - at what amount
of added clay stops the bleeding.
The up ramp does not matter much at the beginning - some glazes may tend to
crawl more if fast fired at the beginning - specially if they start out
wet. I would think no slower than 100C for a glaze firing. I have never
seen any bad results from going fast through the quartz inversion for
instance - certainly I do 200C per hour on a regular basis.
Something happened to my controller with my last bisque firing - I had
reprogrammed at about 250C after an overnight bisque warmup - set the
controller properly (I think) for a 100C rise per hour - noticed something
was wrong when I checked it an hour later - it was at 800C - checked my
controller and the rate had jumped to 999C per hour. I reprogrammed to 50C
per hour and everything proceeded as planned.
I opened the kiln - all mugs - and there is no visible problem that I can see.
I have never had any problems with dunting on the way up - even in my gas
kiln and I am sure it goes a lot faster than 200C per hour at that stage.
Quartz dunting always happen on the way down as far as my 40 years of
experience tells me. If it did happen on the way up the cracks would be
open a bit - because the ware sinters somewhat during a bisque firing.
RR
>More thanks to Ron and John for further responses to my initial inquiries.
>One more clarification, and then, sigh, still more questions.
>
>Re: majolica: I prefer EZ Strokes because I already have them - probably
>30 of them - and I really do paint detailed picturse on large platters.
>But I hear you, Ron, and may have to continue using the EZ's as
>underglazes rather than on top of glazes. And investigate mixing some
>stains in a clear for use more abstractly over majolica.
>
>My main questions continue re. firing schedules. I got the one I
>originally posted (and use) prmarily from one of the folks at Clay Art
>Center, then modified the cooling per R & J's book. The schedule Alisa
>posted keeps a steady 330F f rom 112F to 2228F. I was told to keep it at
>200F to 250F, and go slow (180F) between 1000F and 1150F and even slower
>(108F) from 1894F to my high temperature. On the cooling end, I
>understand what John is saying. It appears that slow cooling doesn't have
>to go all the way to 1100F as I was doing, but only to 1500F.
>
>So . . . since I'm just beginning to learn the whys and wherefores of all
>this, I can't evaluate for myself whether to ditch my slower ramps on the
>way up. Seems like if it works for Alisa, it should work for me, but I'd
>appreciate any comments. I'd certainly love to shorten my firing schedule
>which now takes about 15 hours during which I'm tethered to the studio!
>
>Thanks for listening to me one more time! Hope everyone's having as nice
>a start to the new year as I am: kiln's loaded and my daughter's here for
>a visit. Picture talking and eating, hiking and talking, eating and
>talking, shopping and talking, skiing and talking, eating and talking. . .
>.you get the idea.
>
>Joan
>
>
>
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Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
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