Basic Prop terminology

So much to say so let’s start by discussing some basic terminology involved in making a hand prop for now for those that don’t know. “Pros can skip this part.”

A fabricator or prop maker will take a:

Conceptual design: From the art dept which is approved by the Art director or Production designer (You hope) and scratch build a:
Master : This is the original piece at which a mold is made to reproduce or clean up the part…sometime originals are made of Clay. Other times they’re made of hard material like MDF, Plexiglas or Renshape. From here we get into:
Tooling: Referring to cutting into hard materials with a band saw, knives, drilling etc. or sanded to make a piece ideal or smooth. Quite often different materials are combining to create the desired look.  Sometime a quick mold is made and the pieces is tooled from that.
NOTE: (In current prop making many shops use a C&C cutting machine or a Rapid Prototype machine to create the prototype or the actual prop piece. This technology is unmatched in quality but highly expensive to own such tools. For our sake we will be discussing hand built items.
When my piece is getting to where I like it. I will spray it with sand-able primer. This helps to see any flaws that will appear on the mold. Again the piece is sanded to the desired look. Once you’re happy now you can move onto the:
Mold making: This all depends on what your making if your prototype is made out of clay you can used plaster like (Ultracal 30) to mold your item.  If it’s a hard piece made of plastics them Silicone rubber (GI 1000) is a popular choice. We won’t get into mold making just yet but in a future post. Sometimes you can have a mold that is silicone with a  plaster shell.
Jacket AKA Mother mold: Is an outer hard shell to support any thin floppy materials like a thin coat of silicone. This helps support the shape and is layered over the silicone. This can be made out of Plaster, fiberglass or urethane. It is also a two part to separate and remove your silicone mother mold.
Matrix mold: Is when the jacket is made first, then the inner fluid layer (silicone) is added. (Will discuss later) with so many different techniques it’s best to choose what mold making material is best for the item your:
Casting: Which is the process of creating the part after the mold has been taken apart the prototype/master has been removed. The mold is cleaned up. Now you can fill your mold with materials such as two- part urethane, semi rigid urethane, plaster, rubber, foam rubber…it all depends the purpose of the prop…is it a stunt prop? If so, soft urethane rubber is good. Is it a hero piece? Semi rigid urethane or urethane might be ideal. Is it a break away? The list goes on! This is why it’s so confused regarding where to start, with all these sub categories…I digress.
Clean up: Once your piece is cured (your two part chemical has reacted creating a solid from a liquid…Science! ) now you can take apart your mold and remove and or cut off any excess know as flashing that occurs from the seam or separation of your two part mold. The better the mold the easier the clean up and less flashing occurs.
Paint: Once you’ve cleaned the piece and hopefully not too long now it’s ready for paint. Again depending on what it is you can use spray paints, air brush are usually the most popular. Then the painter will in many cases weather the piece. This is if it isn’t to look pristine but used.

Now you’re ready to hand it to the prop dept of filmmaker who says…That’s great, how much did this cost?  

Silicone (blue) molding material brushed on a prop skull. The (white) mother mold then applied. This two part mold will be assembled together and ready for casting.