Check out this detailed video that covers how to mass cast an object with no flat sides. This video is only for very experienced mold makers or the particularly ambitious. When mass casting a part without a flat side, you must create a two-part mold. We create a two-part silicone rubber mold with a clean parting line and then cast the part with Repro. This process can be used in automotive, mechanical, fine art and film special effects uses.