I've just created my first silicone mould, well, the first part of a two part mould.

I've used OOmOO 30, which is great.

However, I've used a modelling clay called Sculpey III to raise parts in the first half of the mould.

The silicone has cured, and I've attempted to remove the clay, but it's just stuck to the plastic parts and the mould.

Any suggestions on cleaning? Or a better clay?

  • So I used clay to raise parts in a 2 part mold. These were plastic Nintendo Gameboy Color buttons. Apr 10, 2020 at 13:50
  • It was just to rise the buttons off the base of my mold box, then to be removed when I started the second half of the mold Apr 10, 2020 at 13:58
  • posting as a comment because I don't know for sure (couldn't quickly find an answer, I'll look again later), but try a solvent like (strong) rubbing/isopropyl alcohol to remove it, and don't use it again. Polymer clays tend to partially melt plastics--the plasticizers in them break down hard plastics like your buttons.
    – Allison C
    Apr 10, 2020 at 15:19
  • Thanks! That's helpful, any suggestions on a good clay to use? Apr 10, 2020 at 15:21
  • it's been a very long time since I've made a silicone (selastic) mold, but iirc, I used plasticene (non-drying modeling clay) to create the registration "bumps" and pour spout when making the first half, and it removed cleanly from the mold material. I can't speak for plastic, as I was molding from a silver piece.
    – Allison C
    Apr 10, 2020 at 18:29

1 Answer 1


Sculpey is not good for this, it is also expensive.

first you want a clay that stays soft, a simple bulk oil-based non-hardening clay tends to work. I prefer softness #4 but there is a lot of different preferences depending on the material being molded, I was working with fossils where cleanup came second to preserving an extremely delicate original. If your original is tough or disposable go with a harder clay "medium" by most sellers, it makes clean up easier. You can heat it to soften it if it is too hard to work with or compromise and go with a "soft" clay. Some people mix their own clay with clay dust and grease but store bought non-hardening clay works fine, I tried it and never noticed much difference. You want something that is oil-based and non-hardening. if you heat it (and I recommend it) microwaves work OK as long as you get your timing down, don't melt it just get it warm, a toaster oven works better but tends to be kinda of small. I have an old bread oven but I do a LOT of molding.

Don't make your clay solid make ropes and build up to your surface leaving plenty of gaps, only the top half inch or so needs to be sealed, the rest of the clay should have gaps to allow it to be pealed away easily. I have also used lego or wood to build up to where the clay surface will be so only the top inch is clay. If using clay all the way through often I line the original with saranwrap or tin foil, so clay is only contacting the inch or so where the seam will be, makes clean up a lot easier. Just make sure it is not exposed or the silicone will wick down that material and waste a lot of silicon. (note if you use foil you don't want to use a microwave to heat your clay, I burned up a lot of microwaves before I got an old bakers oven to heat my clay.

using a release agent before putting the original in the clay will help, as will a simple dull dental pick for scraping away any left over clay. The cooler and harder the clay is the easier it tends to come off.

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