How to make a plaster mold

Frame on soaped melamine surface, seal outside edge with clay

Sealing edge

Center tile in frame

Brush soap or silicone spray over tile surface

Weigh plaster 1937 g

Add slowly to 1 quart of water, let sit for 2-3 minutes then stir slowly by hand breaking up clumps, not too fast you don't want air bubbles.

When plaster thickens to heavy cream feel slowly pour into frame

Fill frame

Tap table with rubber mallet to bring any air bubbles to surface

After plaster loses its sheen and has hardened some, invert and trim off any extra globs

Use knife or metal strip to bevel all edges

When tile starts to dry a bit, pry out and clean up mold edges

Finished mold, let dry completely before use