How to cast precious two part plaster of paris mold of holding hands?


I made a two part mold of the interlocked hands of myself and my dying mother. I used plaster of paris. I first layed our hands halfway into the a plaster of paris mixture in a plastic basin, with mostly my hand in the plaster, until the plaster dried. I then extracted our hands, with just a little pinching by the mold. I then applied vaseline to that part, reinserted our hands, and poured a batter thick mixture of plaster of paris completely over our hands. When dry, the halves separated easily and hands came out of the molds with a little more pinching.

Now I have this precious mold from which I want to make (hopefully) more than one casting (for family). I know something rigid would have to break the mold to be extracted (i.e. because of the pinching). I don't mind casting in something besides metal.

What are the possible options for processes and materials?

My general guesses are:

- make multiple castings from this mold using a flexible casting material (e.g. silicone). or use the flexible casting to make a better mold

- make one casting from this mold using a flexible casting material and use the to make a better mold

- make a one casting using a rigid carvable material and use this to make a better multipart mold. (I'm worried about doing something destructive, though)

- get a computer scan of the mold and use that to make ...

- turn it over to a profesional. What might it cost?

Thanks for any advice, Michael

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What is your ideal ultimate goal? Multiple metal sculptures (e.g., bronze)?

Here's what I would do. Right now, you have a master negative (the plaster mold).

  1. I would make a master positive using mold-making RTV silicone. This is very flexible and captures fine details. After curing, you should be able to remove it without damaging your plaster master negative.
  2. Make a new master negative out of rubber using the silicone master positive from step 1. I'd probably try mold-making RTV urethane for this step since the urethane is a little harder than silicone and may do better forming the mold protrusions that will reproduce the crevices between your fingers and clasped hands.
  3. Next, I'd use the rubber master negative of step 2 to make multiple working wax positives.
  4. For each of the wax positives of step 3, proceed with traditional lost wax casting in metal.

You can do this yourself, but it may be challenging if you've never done this before. Ideally, you will need a good (i.e., commercial) vacuum pump and improvised vacuum chamber for step 1 and step 2 so that you get all the bubbles out of the rubber as you're casting your molds.

You can buy much of the mold making materials (rubber formulations, mold releases, etc.) from Tap Plastic's online store:

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If you have one of their retail outlets near your location, you should drop in and talk with them for more professional advice.

Hope this helps, Michael

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Make one good positive master from a low-to-medium durometer two-part silicone RTV. Then take off as many negatives as you wish for resin or plaster casting.


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Lloyd E. Sponenburgh

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