Step 6: Encased in algenate!
InstaMold is very simple to use, it is a white powder that when mixed with water forms a jelly like substance (algenate). Follow the instructions on the side of the canister as to how much you will need to cover the area of the box. You will need the algenate to be 1 1/2" deep to get a (fairly) strong mold.
You can use any number of different molding compounds for this step, algenate is by far the cheapest.
The best quality molds are made from silicone rubbers, although not all of them are suitable for use with clay originals.
Algenate molds are fairly fragile and short lived, you will probably get 4-6 castings from an algenate mold if you are careful.