cutting edges
Now you will drill keys and flashing around the new pieces you’ve created. Keys are for precise registration of two or more mold parts so that they will fit together perfectly. Keys can be created by drilling rounded shapes into the positive (no undercuts!) or by placing clay or rubber shapes at even distances around the mold wall you will create.
Flashing is thinly placed (about Vs inch) over all the exposed areas of the mold and trimmed to within Vs to % inch from the edge of the sculpture for your appliance.
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figure 5.13
Flashing placed on the face sculpture. Image reproduced by permission of Mark Alfrey.
The flashing needs to be cut away from any drilled keys. The purpose of flashing is to create space for excess appliance material to escape when the mold parts are clamped together to cast the appliance pieces in gelatin, foam latex, or silicone.
There is a very good reason that the flashing stops just shy of the edge of your appliance sculpture. Do you know the reason? It’s to create a cutting edge for the appliance you will cast later in the mold you’re about to make. A cutting edge is the point where the negative part of the mold comes into physical contact with the positive, creating a separation of excess material that will escape into the space created by the flashing, and the material that is pressed into the space created by your sculpture to make the appliance. When done properly, it will leave you with ultra-fine edges that will be very easy to blend off onto your actor’s skin or overlapping pieces when you apply the makeup.