Step 1
Prepare a 50/50 mixture of borax and boric acid. Either one will work by itself if you don’t have both. Borax is slightly more fluid than boric acid when melted, which aids in the curing process; however, some borax may be carried by the metal during casting.

Step 2
Fill your crucible with the mixture to about 1/3-full for a small crucible, and about 1/4-full for a larger one.

Step 3
Place the crucible with the mixture in your oven and heat until the mixture forms a puddle at the bottom. Hint: Begin heating your crucible slowly to allow moisture to dissipate (heating too quickly may cause severe cracking). Carefully tilt the crucible to allow the mixture to coat the entire interior surface. If it stops flowing, return it to the oven until it returns to a liquid.

Step 4
Once the interior has been covered, pour the excess into a nonflammable container. Allow crucible to cool to room temperature.