Published Sep 2, 2020
There are a lot of ways to put texture into clay surfaces. Clay artists have a knack for finding objects to make impressions with, and, of course, there are a plethora of store-bought texture tools at clay suppliers and craft stores. And most clay artists have some homemade bisque or plaster texture tools in their toolboxes.
Today I am sharing one of those homemade texture tool ideas. This one is a great tool for laying down a pattern quickly and easily over an entire slab. In this post, Margaret Bohls explains how she carves texture, in this case a grid-like pattern, into large plaster slabs and then rolls her slabs on the textured plaster. She then puffs out each square in the grid with her fingers and creates a sense of volume. - Jennifer Poellot Harnetty, editor
I make my vessel forms using clay slabs pressed onto textured plaster molds. A textured pattern is carved into the plaster surface using a long, straight edge and the same loop tools used for carving clay. I make my molds large enough to be at least as long and as wide as the largest slab needed for any given project. My mold is about 1½ inches thick and measures about 15×30 inches.
Pouring a Plaster Slab
To make your own plaster slab you’ll need a large, smooth, impermeable surface to pour on, such as glass, Plexiglas, or Formica. Make sure the work surface is level. With a Sharpie marker and a ruler, draw a rectangle on the work surface the size you want the mold to be. Either set up cottle boards on your rectangle and clamp them together to create walls to contain the plaster (figure 1) or use waster clay to build a thick, sturdy wall around your drawn rectangle.
The wall should be about 2 inches high. For clay walls, reinforce the outside of the wall with a fat coil of clay to be sure it won’t collapse under the weight of the liquid plaster. Use a flat sided rib with a right angle to smooth the interior clay wall’s surface. Be sure either the clay walls or the cottle boards are sealed at the joints with coils of clay so the plaster won’t leak out.
Determine the volume of your mold and mix up an appropriate amount of plaster. Use #1 Pottery Plaster for casting or pressing clay. Once the plaster is mixed, pour it slowly into one spot between your clay walls, making sure not to splash or make bubbles. Jog the table several times to be sure the top of the plaster levels out. Allow it to set up thoroughly then remove the clay wall or cottle boards and lift or slide the plaster off the casting surface. Use a Surform tool to shave off any sharp edges and then sand the back of the mold (the side that was up during the casting process) using first a green kitchen scrubbie pad and #400 wet-or-dry sandpaper. Sand the mold under water. Until the plaster cures completely, it will be fairly fragile so handle it carefully. Sanding the back side of the mold allows you to carve texture into both sides should you want different textures or grids.
Carving the Textured Plaster Slabs
Lay the plaster slab onto a smooth, level surface. I use a ruler, a square, and a pencil to draw a diagonal grid onto the plaster surface, but of course almost any drawing can be made into a carved texture. To carve long, straight lines, use a hardened-steel loop tool with a narrow loop (about 1/8 inch). Lay a straight edge along the drawn line and pull the loop tool along the edge of the ruler (figure 2). It takes two or three passes to get a sufficiently deep line. Once all of the lines are carved in one direction, turn the mold and carve lines in the other direction to make a grid.
Clean the mold by rinsing it under water. You may now carve the reverse side of the mold with a different pattern or grid if you choose. The size of the squares in the grid is up to you. I have several molds with different sized grids between 1 and 2 inches.
Caution: Remember that clay and plaster do not mix. Set up a mold making area someplace other than our day-to-day clay working area. Mix, pour, clean, and carve your plaster in an area where clay will not come in contact with even the smallest plaster bits.
Texturing Clay Slabs with the Textured Plaster Slabs
To texture clay, first roll out and compress a clay slab. Drop the slab onto the mold and then slap it down into the texture using your hand. Run a rolling pin over it, and finally go over it with the plastic rib to completely smooth the back of the slab and make sure clay has filled in all the texture carved into the mold (figure 3).
Gently, lift each slab off of the mold, flip it over, and cut it to the appropriate size needed (figure 4).