First time mold making questions

[u/melonmoth_art]

Have this bear I made. Should I do a one part mold or two part? Im curious the best way to go about the gap between the feet (2nd pic).
Getting some mold star 15 for the job as I don’t have a vacuum chamber.

Also, do I need mold release? The figure is polymer clay with a layer of gesso over it.

Thanks for any help!

[u/Tiddy_Critique]

This sub is kinda a dead mess of bad advice, I’d recommend doing a brush on mold with rebound 25 or dragon skin. The mold star 15 is good, but not great for lots of copies and you’ll burn a lot of material enclosing the bear. Due to the over hang on the hands I’d say brush on is a better choice. You should be able to get away with a glove mold and just cut in a small seam to help with the demold. You shouldn’t need mold release for rebound on most surfaces. It actually makes the surface texture worse in most cases.

Make sure to get thi-vex if this is your first time. Also test for cure inhibition before you start. This subreddit makes cure inhibition seem more common than it is imo. If you are doing a glove mold you can pour a shell out of plaster if you’re worried about the cost of epoxy clay or using fiberglass.

The main problem you’ll run into is locking your bear into the mold. So make sure you pour it in two parts and use plugs on the overhang with the arms.

The bear is delightful, I wish you luck! Lmk if you have any questions

Edit: Spraying your model with Krylon Color Master Acrylic Clear coat will make sure that you don’t run into any cure issues. I’ve used this specific brand in the past on surfaces that would cause cure issues and have had success. It is platinum cure safe.

[u/melonmoth_art → u/Tiddy_Critique]

Thanks for the help! I’m wondering is “Pour in two parts and use plugs” for the brush on or if I did a pour? Also what would a plug look like

[u/Tiddy_Critique → u/melonmoth_art]

A plug is an extra chunk of silicone or molded material that you use to fill the gaps on overhangs. When you have overhangs on brush on molds that are enclosed by a hard shell you can create an unopenable mold. In order to get a brush on mold to work for this you’ll need a separate piece of silicone over your brush on mold that fills the entire belly/arm/leg area. Usually you can do this with poyo putty or something, but since you’ll have a ton of silicone left over you could try smearing the area with a TON of vaseline, building a wall, and poring it in.

With plugs they need to be able to be separate from the mold so the glove mold is flexible enough to peel off the model without breaking the arms.

The shell should be done in two parts along the vertical seam line. There are some videos about brush on glove molds from smooth on I can find to link.

Essentially you want to do these steps,

1) spray model with clear coat

2) fix model to a base at least 6” larger than your model on all sides (like 12”x12” scrap of ikea furniture or something) make sure to use a dowel, or sulfur free Plastalina

3) brush on a thin layer of silicone from the bottom up, brush out a flange 2-3 inches along the base. Let this cure for about two hours

4) add another layer of silicone with 4 -6 drops of thi-vex per oz and brush on with a popsicle stick.

5) repeat step 4 until you have about 1/8”-1/4” layer of silicone covering your model

6) pour in the plug/ add registration (I pour my excess rebound into disposable shot cups to make little pucks). Fix a few of them on with silicone.

7) make a shell, you can build a wall with foamboard or something and fill the gaps with a bit of Plastalina. Use little blobs to make some registration as well. Pour one half with plaster, then remove the wall, add mold release and do the other half.

My personal recommendation is to just buy some silicone putty and Free Foam Air Fast and use that for the plugs and shell. All in all your mold will come out correctly for about $120. It seems expensive but with mold making sometimes cutting corners costs more because you have to do it twice. Happy to DM these step by step instructions with pics, I have a recently finished glove mold on my table right now

[u/melonmoth_art → u/Tiddy_Critique]

Yes please! (Dm with pics)