Flo Fahrenheit on sat 25 feb 12
Wyndham
It sounds like the piece of clay you put over the hump is too big, and =3D
thus oozes around the edges of the mold when it is pressed down. Use =3D
less clay, or trim off the excess when the clay is still moist, but be =3D
careful not to chip into the plaster, you don't want that in your clay - =
=3D
it will explode in the kiln. I put clear packing tape around the edges =3D
of my molds to protect the delicate edges, this allows me to trim the =3D
edge of the clay without hitting plaster. The clay is likely to stick to =
=3D
the tape, so here are a couple of methods to prevent that!=3D20
1) Lay several 1-2 inch wide torn strips of newspaper into or on top of =3D
the plaster mold in the shape of an asterisk (*) to act as a barrier =3D
between the clay and the mold. The clay slides over the paper as it =3D
shrinks. If you tear the newspaper in the correct direction, it =3D
conveniently tears in a straight line!
2) Cornstarch works well as a mold release. I put it on the clay, not =3D
the mold. It doesn't leave any residue or discoloration on the clay =3D
after it is fired (and it seems to cause no problems if you wedge it =3D
back into the left over clay). I keep about 1/2 inch of cornstarch in a =3D
3 x 5 inch plastic container with lid, and store a dedicated fluffy sake =
=3D
brush right in with it. The brush is an excellent way to apply a thin =3D
layer of powder all over the clay slab. I have also seen it put into a =3D
salt shaker or spice bottle with holes, then you sprinkle it on and use =3D
your hands to smear it around. The cornstarch is a great release to use =3D
on sprig molds too.
It also sounds like you are leaving the clay on the mold too long. When =3D
using a hump mold, I blow the formed clay with a hair dryer to firm it =3D
up, then carefully remove it from the mold as soon as possible, =3D
otherwise the clay will shrink and crack.
Flo Fahrenheit
Grass Valley, CA=3D
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