The simplest, easiest, and best mold you can make for casting resin parts is a one-piece silicone rubber mold.
If you're tired of the tedious process of molding clay into a mold, here's a video. It takes a long time to build a clay dam around the model: - Pour half the rubber, wait for the clay to dry - Remove the clay and clean the model - Apply mold release agent and pour the other half - Wait for the clay to dry - Then separate the mold.
Then you'll find that the dividing line is long, messy, and very difficult to clean. It's a real pain!
There must be a better way - and it exists!
A mold cutter is easy, fast, and produces the best possible dividing line.