CT-Rich
Contributor
Ah... that brings back memories of experiments past... nothing like the effect of hot lead on damp plaster.I have used plaster of Paris for lead molds. It will make a number of casting before getting too damaged from use. Be SURE it's completely dried out (a couple hours baking in a hot oven is a good idea) before using it or steam explosions can happen. Flying hot lead is not a fun thing to be around.
I like the idea of lining the plate with foil. If you want to make them to bolt into place, put stainless steel bolts through the holes with a nut on either side so the head of the bolt will be embedded into the weight. Disclaimer: this is an idea I have not tried.