Animating with Stop Motion ProTM that can be easily animated. For creatures such as dinosaurs, the anatomy should be sculpted for the most common pose of the creature. The best procedure for including an armature is to make the armature first and sculpt around it to ensure that the skeleton will fit inside the figure. This is not always possible, and in pro- fessional circles the sculpture and armature building will commence simultaneously and final adjustments to the armature will be based on the plaster mold. Making the Clay Dam Once the Plasticine original is made, you will want to screw in the tie-down bolts to the feet to provide a way of registering the armature within the mold. In Kathi Zung's tutorial, she also advises animators to project a mounting rod out of the top of the head so that the armature is registered within the mold in three places (the tie downs and head) and create a "handle" for the puppet for subsequent modeling chores. At this stage, we begin to rest the original in a bed of water-based clay to provide an organic dam that will allow our plaster to only mold up to the halfway point of our sculpture to avoid what is known as undercuts. An undercut occurs when the mold's cavity captures the casting material and prevents it from coming out of the mold. An example would be pouring plaster into a rubber bowl. A bowl being a container that funnels outward has no undercuts and the plaster can be removed from the mold easily. If, however, we poured plaster into a narrow- necked bottle, the hardened plaster would be captured by the narrow neck and could not be removed unless we broke the bottle. Fortunately, rubber casting is more forgiving of undercuts than plaster, as it can flex past minor undercuts. Water-based clay is used, as it is soluble in water and provides a good working material that isolates well from the oil-based clay. Water will dissolve and smooth the water-based clay while leaving the oil-based original unaffected. The final step in making your dam is to include clay keys on the flat face of your dam. A key is simply a tapered rectangular shape of clay that will provide a positive interlocking mechanism for the two mold halves. Side A will have a depression, and side B will have a protrusion that exactly fits the depression. This guarantees that the two mold halves will fit together in perfect register. Once you have made your dam, a plastic sealant called Crystal Clear is sprayed on the surface of the clays to provide a uniform coating in preparation for the plaster. Mixing the Plaster Because the casting process requires durability and heat resistance (you will be baking the rubber mixture in the mold), the best material to use is dental stone or ultra cal. These hard materials are a cross between plaster of paris and cement. They take excellent detail, are extremely hard, and stand up to heat well. The mixing of ultra cal should be done with the use of rubber gloves, as the material contains lime and also gets hot when curing. Always sift plaster into water instead of water into plaster. This is critical to obtain a good mixture without air bubbles or dry pockets. Patience is the watchword here. In a rubber container of water, sift in the plaster until you have created a small hill of the powder that extends above the water line by about an inch. At this point you wait and watch until the plaster "slakes." Slaking is when the powder starts to absorb the water and look wet. When your hill of plaster has become saturated with water, you can then begin to stir and mix the solution. If you see a layer of water above the plaster, then you will need to sift a bit more plaster until you obtain a smooth mixture. Once the plaster is mixed, you make the cast in layers and reinforce with burlap fabric. Zung demonstrates the excellent shop practice of smoothing the shape of the mold for a safe and professional finish. 162