Jonathan Kaplan on mon 25 sep 00
earthenware.??
>Good morning,
>
>I am posting this for a friend who has been digging some local clay .
>blunging it and then putting it through screens.
>
>The clay is very plastic, throws well straight from the ground, and seems
>mature at cone 04. Takes a white majolica glaze perfectly...BUT...
>there are lime pops that form after the pot sits for a day or so.
>They rise to the surface of the glaze and can be crumbled with a fingernail.
>( I am making an assunption that they are lime,,or some form
>of calcium.)
Lime is hydroscopic and will expand when it comes into contact with water,
eg from glazing. It expands and pops out from the surface. You can test for
lime by taking the white residue from the center of the pop out and drop it
into hydrochloric acid. If it fizzes, its lime. ''If you are blunging it to
a slurry and passing it through screens, it should remove the lime. Try a
smaller screen, like a 50-60 mesh sould be more than sufficient.
You could also test the dry clay powder with acid and look for fizzing.
Jonathan
>
Jonathan Kaplan
Ceramic Design Group LTd/Production Services
PO Box 775112
Steamboat Springs, CO 80477
(970) 879-9139 voice and fax
http://www.sni.net/ceramicdesign
UPS: 1280 13th St. Unit13
Steamboat Springs, CO 80487
John Guerin on tue 26 sep 00
earthenware.??
In a message dated 9/25/00 7:52:07 AM Central Daylight Time,
potter@WESTMAN.WAVE.CA writes:
<< I am posting this for a friend who has been digging some local clay.
blunging it and then putting it through screens.
The clay is very plastic, throws well straight from the ground, and seems
mature at cone 04. Takes a white majolica glaze perfectly...BUT...
there are lime pops that form after the pot sits for a day or so.
They rise to the surface of the glaze and can be crumbled with a fingernail.
( I am making an assunption that they are lime,,or some form
of calcium.)
Is there anything that can be done to solve this problem? >>
Do your final screening through a nylon mesh bag which can be obtained at a
paint store. These nylon bags are used by professional painters to strain
the paint so it will not clog up the fine power spray nozzles. The bags fit
in a five gallon bucket and if you get the ones with the elastic tops, they
fit snug over the edge of the pails. The nylon mesh is very fine and will
remove any fine particles.
Good Luck,
John Guerin
Tucson, AZ
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