Kim Hohlmayer on fri 15 aug 08
Hi All,
I learned this technique from a paper casting class and found it works the same for clay press molds big and small.
Take a sheet of acrylic glazing material like Plexiglass making sure it's a little bigger than whatever you want to create. Using Plastalina or a similer oil based clay sculpt your original directly onto the acrylic sheet. When it is just as you want it put it inside a large plastic bag and put the plastic bag inside a box just a little larger than the acrylic sheet (yes, just an ordinary cardboard box). Open and spread the bag over the edges of the box. Now you should be looking in the bag in a box and seeing your sculpture. Mix plaster per directions and pour into the bag/box directly over your original. Make sure the plaster is at least two inches deep over the highest point of the original.
Once the plaster is dry - and , yes, it will take a good while as in days - carefully turn the box over and pull it off the plastic bag. Then take the plastic bag off the plaster. At this point the plaster is still on the original and its acrylic sheet. Holding the acrylic sheet carefully and gently twist the acrylic sheet at opposite corners. If the plaster is truly dry the mold should instantly pop loose. Turn it over and lay it plaster-side down on a table. Gently lift out the original, plastic sheet and all.
Because the plaster will not stick to either the acrylic or the Plastilina you never need to use any sort of separator.
One point I almost forgot, when you pour the plaster into the box/plastic bag form gently tap the box on the table until it looks like all the air bubbles have migrated to what will be the bottom of the mold when you are done. --Kim H.
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