Sharkymeg

So I’m new to slipcasting, and I have this silicone baking pan I want to basically translate into a plaster slipcast mold. I’m assuming what I need to do is put some kind of material into the pan to make into the shape- wax? Soap? Not sure. -and then make a plaster mold from that shape. What would work best? It’s a silicone pan so pretty flexible, and the outside isn’t the same shape so I can’t just make a mold with the pan itself, but it doesn’t have any undercuts, so I’m planning to just make a simple one piece plaster mold. (If it helps, it’s the Ikea tartbak,and I’m just wanting to make a mold of the bottom portion to avoid the undercut). Thanks!