how to start pouring plastics

I want to start pouring my own plastic. I would like to make a diy mold and was wondering if anyone knows how?

Google making molds from plaster of Paris.

I make mine from Bondo fiberglass resin. I find a plastic container that at least 2 baits will fit in. I use double sided tape and stick the baits down. Then I use a vegetable oil spray and coat the baits and inside the container. I mix up the Bondo and pour it into the container. I want it to be at least 1/2” thicker than the bait.

Then I go away and let it cure. When cured I take the mold out, remove the baits and touch up imperfections with a Dremel tool.

Youtube is your friend.