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There are lots of articles and how-to guides on the web showing how to replicate a plastic, wood, or metal object by making a silicone mold and using a hard acrylic or epoxy resin to create the object.

I have the opposite problem. I want to replicate an object that itself is made of silicone. My current plan is to try to create an acrylic mold of the original silicone piece, and then to use the acrylic mold to cast silicone. Is there any other way to go about this that would make sense to someone with more knowledge than I have?

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  • Off the top of my head (but untested), if I wanted to make something that was made out of my preferred mold-making material, I would probably cover the original with tin foil, using my embossing tools to smooth the foil into all the nooks and crannies, and maybe some modelling clay to smooth out the foil seams. Once the original was completely protected within its foil armor, I would then cast it as normal.
    – Henry Taylor
    Commented Jul 9, 2018 at 13:26
  • On further thought (but still untested), you could probably just use mold release spray (which is used in two-part silicone molds so that the top and bottom parts of the mold don't stick together) in place of the tin foil.
    – Henry Taylor
    Commented Jul 9, 2018 at 16:21
  • Thank you for the suggestions. The item I want to reproduce is rather expensive, and I don't want to risk not being able to release it. Also, I want to make many copies in silicone (it's an earplug). Were I to use a silicone mold, I would have the same risk every time because I am casting in silicone.
    – ProfessorE
    Commented Jul 10, 2018 at 2:32
  • For that second issue, you might also want to search the term "silicone on silicone casting" on youtube. There seem to be a few mold release products which can handle that requirement. Not sure that any of them are safe for your expensive original, but once you somehow get the first mold, creating silicone castings seems feasible. Have you considered self-hardening clay for the first mold?
    – Henry Taylor
    Commented Jul 10, 2018 at 4:16
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    Henry: It would be great if you summarized your comments into a post, so that it could be marked as an answer. self-hardening clay might work, but I worry about shrinkage - it's an earplug and small percentage shrinkage matters.
    – ProfessorE
    Commented Jul 13, 2018 at 18:28

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I agree with #torjek that a separator (mold-release) spray or liquid would make it possible to caste a silicone object with silicone as the mold making material. The benefit of getting good at this technique is that you could then caste replacement silicone earplugs using the mold which you just made out of silicone.

If you need more protection for your original, you could probably cover the original with tin foil, using embossing tools to smooth the foil into all the nooks and crannies, and maybe some modelling clay to smooth out the foil seams. Once the original was completely protected within its foil armor, it could be caste as normal.

You might also want to search the term "silicone on silicone casting" on youtube. There seem to be a few mold release products which can handle that requirement. Not sure that any of them are safe for your expensive original.

Have you considered self-hardening clay for the first mold?

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If you're using a two-part pourable silicone, you can make a mold of the item with a reusable gelatin-glycerin mold material you can make at home. There are a lot of variations on the formula resulting in different characteristics. The material, itself, is also molded into special effects prosthetics instead of using latex rubber. To investigate the variations, Google "gelatin glycerin reusable mold". A good start is this tutorial by a chemist who dabbles with stuff like this to refine it.

You warm the material in a microwave oven and it turns into a liquid. You pour that over the item in a form or container. When it cools, it's a rubbery mold of the item that captures fine detail and is dimensionally stable.

You can't cast hot materials in it because that would melt the mold. For resins that are very exothermic, you can often freeze the mold and then use it.

You can get several uses from a mold. Then you just warm it back to a liquid and make a new mold.

The material has a long shelf life. You can make a big batch of it, use what you need for a particular mold, then either save the mold or melt it and add it back to the supply.

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You can use a silicone to make a mold in this case too. I've done it in the past. You just have to spray the original silicone piece with the separation spray before you pour the silicone into it like you do the first part of a two part mold.

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