First step in making the molds is actually reworking the original clay pieces, filling in all of the holes and cleaning up the undercuts. All of which makes it easier to cast the final piece. This part of it took me almost 3 days, but it will save me a lot of time and trouble later.
Next I make a box around the pieces to hold the rubber mold and the plaster shell. I am dealing with liquids, which means of there is a hole in my box, the mold materials will leak. Not a pretty site, very messy and a lot of work to clean up.
The mold material is plastic when it dries, so I can use cardboard as my box as the plastic will not stick. Below are the chemicals I use to make the rubber molds (top row), the plaster shell (boxes) and the bronze cold castings (the jugs). Each is a combination of mixing two chemicals together. Temp. and humidity is critical +- 5degrees.