Removing the castings from the investment can be a challenge. The investment, which is baked at very high temperatures, turns into a glass-like substance that can be difficult to separate from the cast pieces.
Most manufacturers use hydrofluoric acid, which is extremely dangerous and must be handled with utmost caution. Always use rubber gloves, a rubber apron, and a respirator that filters small particles from the air.
A small shop may wish to consider a safer devesting agent for platinum investment as a substitute for hydrofluoric acid. Ask your tool supplier; there are many brand names. You can also mix your own substitute using the following formula (percentages are given by weight): 25 percent sodium hydroxide, 25 percent potassium hydroxide, and 50 percent deionized or distilled water. (The sodium hydroxide and the potassium hydroxide should be in pearl or flake form.) Combine all three solutions in a stainless steel container, and heat (do not boil) for 25 to 40 minutes. Be careful mixing, since the three ingredients will naturally heat up when combined.
~Jurgen
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