Applying Colored Slips to a Plaster Mold Before Slipcasting For Surface Pattern

Adding Colored Casting Slip Inside Molds


I first saw the work of Peter Pincus when I juried the 2012 ICAN Members Exhibition (formerly Potters Council). It was a large bowl with a brightly colored striped surface that fit the exhibition’s theme “The Chromatic Edge” perfectly.

When I saw the piece (see below) in person when setting up the show at NCECA, I was blown away. And very intrigued as to how he made it. The lines of color didn’t seem stenciled or screen printed but they were so crisp. In this post from the Ceramics Monthly archivesPeter shares his super cool process. Mystery solved. – Jennifer Poellot Harnetty, editor.

The Process

This bowl by Peter Pincus was part of the 2012 ICAN (formerly Potters Council) Members Exhibition at NCECA.

My pieces begin as profiles on the wheel, fabricated precisely from a drawing, but thrown wider than I intend the finished piece to be—about 1½ inches larger in diameter. As soon as the piece is thrown, when the clay model is still completely malleable, I assemble metal flashing around it, leaving two inches of space between the flashing and the widest diameter of the model.

Ceramic Mold Making Techniques

Learn to make and use bisque molds and plaster molds, plus get casting slip recipes when you download this freebieCeramic Mold Making Techniques.


I pour plaster in between the piece and the flashing, and allow it to cure as the wheel turns. When the plaster hardens, I lift it off of the wheel, turn it over, and pull out the clay model from inside (the wet clay peels right out), turn it back over and sketch lines to be cut with the band saw. The extra 1½ inches in diameter is important at this point. It leaves room for complex, angled cuts that enhance the original form. The cuts are made on a bandsaw (1), the remaining pieces are sanded and meticulously cleaned, and they are reassembled and keyed together with fresh plaster sections added on the top and bottom (2).

pincus21Each mold is then subjected to a lengthy and damaging process of repetitive slip layering and knife cutting. Colored porcelain slip is slathered onto the casting face of the mold with a 1-inch brush (3). A fresh X-Acto blade is then used to draw across the surface of the leather-hard clay, often digging deep into plaster (4). The trim easily lifts from the plaster and is tossed in the nearest trash can (5). New colored slip is added, cut, and trimmed (6) and so on until the composition is complete, the mold is cleaned up, assembled (7), and cast in porcelain.

When removed from the mold, the work is relatively beaten up (image 8). It must be scraped and sanded, bisqued, fastidiously wet sanded, flattened on glass, cleaned, and fully dried in preparation for a smooth coat of clear glaze.


Peter Pincus is an artist and instructor living in Penfield, New York. He received an MFA in ceramics and a BFA in ceramics and metal fabrication from the New York State College of Ceramics at Alfred University. To see more of his work, visit

**First published in 2012.

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