For the Love of Plaster

Just finished teaching a four week class on Basic Mold Making. I'm afraid I may have learned more than my students did.  It's quite a mind bender going back and forth between positive and negative, hump vs. slump...  At the end of the fourth week it was just beginning to click.

I personally have come a long way in my distaste for mold made work.  In my own work I have found a way to create unique forms from the molds.  My favorite mold is a clover shaped bowl made from three separate masonite templates (Andrew Martin style).  The clover shape evolved from thrown and altered square dishes made on the potter's wheel.  I have long since left the wheel not that I was ever that devoted to it.  I prefer slab building.

Thrown and altered

The desire to excessively decorate each form inside and out sent me looking for quicker methods of forming.     I scour the shelves at the thrift store for inspiring shapes as well as vintage glass ware with interesting textures. In the basic mold class we cast simple one piece molds from such a prototype.  Some shapes are better suited as a slump mold such a textured candy dish.  The soft slab is laid inside the mold.  Other shapes we cast the interior/negative space to create a hump of plaster that the slab can cover.  Texture can be applied to the exterior with hand carved stamps. I also try out different styles of feet.  If there is a particular foot I really like or I want to make a set of bowls.  I can set up the clay on the hump mold then cast the form with plaster to create a slump mold.

Clover shaped press mold

Secondary molds are those generated from the primary/basic mold.  I fill the basic mold with clay alter it and cast the new form in plaster.  Sometimes multiple parts of the same basic mold or different molds can be assembled together to generate fresh new shapes.

Plaster sets quickly but the subsequent steps to a finished fired form takes weeks.  Each mold takes a week to dry out after it is made.  If you try to use it too soon it will still take days to a week to get the clay to release from the mold.  I play with the mold for another week.  Casting it with different edges or feet.  A third week for playing with pattern. Dry. Bisque. Glaze.  A month later I'll know if the shape works.  Some are prone to warp or distort.  Trial and error can resolve most such problems.  I have the most problems with circular molds.  Reinforcing by thickening the edge usually helps the circle stay true.