[Figure 3.59] Klean Klay starting to be built around the sculpt.

The sculpt is surrounded completely by a bed of a different kind of clay, commonly a brand called Klean Klay (http://www.kleanklay.com), which is not sulfur based and is ideal for the mold-making process (Figure 3.59). Klean Klay is not recommended for creating the actual sculpt, but it works well for making molds. The clay bed is continually smoothed out and wrapped around the sculpt with a palette sculpting tool so that it is airtight and lines up exactly through the midpoint in a perfectly straight line around its perimeter. The point where the clay bed touches the sculpt is where the seam will be located when both halves of the mold are put together and pulled apart. In many cases, this is at the exact equator of the sculpt, but depending on the design of what you are molding, it is useful to find a point on the sculpt where the seam will not be very visible to the camera. In the clay bed, registration points called keys are created using marbles or any other round or square objects, which will help both halves of the eventual mold to fit together (Figure 3.60). It’s best to plan ahead when figuring out how you plan to get the silicone inside the mold. It’s possible to just pour it into the open molds, but you might prefer to have a hole for pouring it in while the mold is clamped shut. In this case, it’s a good idea to sculpt in a pry point for sticking in a tool to help pull it apart later. You also may want some exit channels built in so you know that the silicone is flowing through the entire cavity all the way to the highest point (like the fingertips for a full body cast). The idea behind the mold itself is to make it as perfectly smooth and functional as possible, think ahead to how you will fill it and get it apart, and think of it as two puzzle pieces that fit together around your sculpt.

[Figure 3.60] The clay bed is complete with keys sculpted in.

Next, the sculpt in its clay bed needs a wall built around it in order to hold the shape of the first half of the plaster mold (Figure 3.61). The wall can be built from almost anything, such as slabs of clay or, in this case, large-sized Duplo or Lego blocks. The smooth, square shape created by the blocks provides a nice surface for the mold to be built against. To avoid leakage and air pockets, the corners of the Lego fortress can be patched with more Klean Klay.

[Figure 3.61] A wall made of Lego blocks is built around the clay bed and sculpt.