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jiggering & mold release

updated sun 26 feb 12

 

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