Lori on mon 24 oct 05
Hi there,
I threw a ginger jar and lid (slightly domed lid approximately 3 1/2"),
bisqued, then glazed them both, and fired to ^6 electric. Since I wanted the
shoulder and lip of the jar to be glazed, I fired the lid separately,
supported on a tripod, like this /_\ . My question, the lid warped
terribly...why did this happen and how do I prevent it in the future?
Thanks for your help...
Lori
Froggy Bottoms Pottery
Port Townsend, WA
Jeanette Harris on tue 25 oct 05
>Hi there,
>I threw a ginger jar and lid (slightly domed lid approximately 3 1/2"),
>bisqued, then glazed them both, and fired to ^6 electric. Since I wanted the
>shoulder and lip of the jar to be glazed, I fired the lid separately,
>supported on a tripod, like this /_\ . My question, the lid warped
>terribly...why did this happen and how do I prevent it in the future?
Hi, Lori,
Most likely, the lid didn't get even support to maintain it's shape.
Next time make the domed lid with a long lip that will fit into the
jar. (i.e. dome and long flange.) Measure carefully while making the
lid and jar top. Be sure when you're forming the jar top and lid to
allow for the glaze on the outside of the lip--that there is plenty
of 'knock' or slippage when you rattle the lid in the jar.
I'd advise making several lids and choose the one that works best.
You can throw the lid upside down by making a bowl with a rather
thick bottom and bringing the rim up to create the flange that will
fit inside the neck of the jar.
The top of the dome can be trimmed to the right thickness after it's
leather hard.
When you're ready to fire the pieces, you can glaze both and fire
separately by making sure that you clean the inside and outside of
the flange carefully (or you can wax that part) and set the lid down
on a tile that has been dusted with aluminum hydrate or painted with
kiln wash. This way, the lid will get uniform support and fire true
to fit the jar.
You could also not glaze the inner rim and outer side of the flange
and fire the two together, but that's a bit trickier.
( ) -dome
|____| -flange
--
Jeanette Harris
Poulsbo WA
Potter's Council member
William & Susan Schran User on tue 25 oct 05
On 10/24/05 11:56 PM, "Lori" wrote:
> I fired the lid separately,
> supported on a tripod, like this /_\ . My question, the lid warped
> terribly...why did this happen and how do I prevent it in the future?
The lid warped because it was fired on the tripod glaze stilt.
As the clay is fired to the higher temperature, it shrinks.
The areas on the edge of the lid that contact the stilt were stuck and could
not move, thus the warping.
Next time, put your lid directly on the kiln shelf, with perhaps a sprinkle
of alumina under it to facilitate its movement while shrinking.
--
William "Bill" Schran
Fredericksburg, Virginia
Judi Buchanan on wed 26 oct 05
Put a small stilt on a post and suspend the lid from that. Or you could
leave a small unglazed area inside under the knob and rest that area on a
post.
Judi Buchanan,Flutter-by Pottery
> I fired the lid separately,
> supported on a tripod, like this /_\ . My question, the lid warped
> terribly...why did this happen and how do I prevent it in the future?
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