In this video, Milo shows how he makes a prop wrench that looks exactly like a real metal casting. The casting is made using Smooth-Cast™ 325 resin and real metal powders in a process called cold casting.
Milo uses clay and alginate to split the model down its halfway point. Then, the first half of the silicone is poured. After this first half cures, the mold is flipped and the alginate and clay are removed. Then release is applied and the second half is poured.
After the original model is demolded, smooth-Cast™ 325 resin is mixed with So-Strong™ colorant and metal powder. This mixture is poured in the mold and allowed to cure, which creates a casting.
The casting is burnished with steel wool, and finished with a thin layer of shoe polish which is buffed.