I did this at TechShop Menlo Park. http://www.techshop.com
Since I do a lot of metal casting and therefore make a lot of plaster investment molds, I wanted to come up with a formula that works best to have consistent quality results with my castings. So I did several tests. If anyone has suggestions and advice, please do share.
Step 1: Test One
Using a scale we measured 7 parts water to 10 parts plaster following a formula we found on line. We added baby powder for talk (8 percent of the weight of plaster) also as suggested online. We mixed with a drill and a mixing attachment. The formula was looking way thin and came out with a lot of bubbles.
Step 2: Investment
We decided to use a hand as a direct investment. The hand was dipped in oil first to make sure it will come out of the mold once set.
Step 3: Outcome
The plaster started to solidify and get warm, so the hand was pulled out. The mold was crackly and crumbly.We were not thrilled with the results especially after the long hand claustrophobia session.
Step 4: Take Two
This time we measured out almost two parts plaster to one part water and mixed gradually adding plaster to the water to minimize bubbling. We used no talk this time.
Step 5: Better Results
This time the mold came out way better. Now it will be cured for many days to make sure there is absolutely no moisture in it before we pour molten aluminum in it to make a hand casting.