Ray-Vin Lost Wax Casting Primer
You cannot use just any plaster for investing casting.
Investing plaster contains crystalline silica and you should use a particle filtering respirator when working with the plaster.
There are several brands on the market and prices range from $20 for a ten pound pail to $90 for a hundred pound drum.
Swest, Inc. is one supplier.
Water is mixed with the plaster in a ratio of 38 to 40 parts water to 100 parts powder by weight.
Mix for four minutes.
If you have a vacuum pump, vacuum for 1-1/2 minutes to remove bubbles.
Pour the investment down the side of the flask so it can rise up around your model pushing the air before it.
Vacuum again for 1-1/2 minutes or vibrate to get bubbles to rise to the top.