Monthly Method: Tile Molds with Flexible Dimensions Glen R. Brown

Appears in the February 2015 issue of Ceramics Monthly.

Having an open-face plaster mold with flexible dimensions provides a lot of options when slip casting tiles. To make a mold like this, I cast a large flat plaster slab, as well as long thin plaster strips of varying thicknesses. (The strips shown here resemble pieces of wood, but they really are plaster!) Creating a tile using these molds starts with drawing a rectangle the size of desired slip-cast tile onto the large plaster slab (1). I place plaster strips around the drawn rectangle, to create a space into which casting slip will be poured. The space inside this open-face mold is approximately 15 x 10 x 1½ inches. 

Once the narrow strips are arranged, I am ready to pour casting slip into the mold. I mix the slip with paper pulp and sand, thus making it very thick. Therefore, it is not necessary to dam the cracks around the plaster strips with clay to prevent slip from escaping the mold (2). If using a thinner casting slip, to avoid leaks it would be necessary to seal the cracks with soft coils of clay placed on the outside edges where the plaster strips and slab meet.

I pour the casting slip into the open face mold (3) and check to make sure the slip is level with the height of the plaster strips that create the mold (4). Next, I place plaster slabs onto the top face of the freshly poured tile to create patterns in the face of the tile. Note the spaces between the slabs (5).

The casting is left in the mold for at least 24 hours to allow water from the slip to be drawn into the plaster.

The next day, I remove the plaster slabs from the top of the cast tile (6). The linear fissures were created by the spaces that were left between the plaster slabs placed on top of the slip. The holes were created by air pockets created between the slip and the plaster slabs during the casting process. When dry, the tiles are once-fired to cone 01 in an electric kiln. No glaze or other surface treatment is applied. To hang the tile, a ¾-inch deep, wooden panel with an inset wooden cleat is epoxied onto the back of the tile. The rectangular dimension of the wooden panel is smaller than the tile so that it isn’t visible when hung. To ensure that the epoxy effectively attaches the tile to the wooden panel, I use a grinder and drill to cut angled holes and grooves into the wood face and the back of the tile before gluing.