Step 3: Mixing and Setting

NOTE: The vinegar smell here is normal. Silicone caulking is mixed with acetic acid to help it cure. The fumes are harmless, but you will probably mix this outside.

To mix your molding material add the ingredients in the following order:

1. Measure out your Silicone into plastic cup (1oz)
2. Add appropriate amounts of Glycerin (3 drops)
3. Add appropriate amounts of Paint (1 Drop)
4. Add appropriate amounts of Mineral Spirits (.5oz)
5. Mix with plastic silverware until the paint is dispersed through the mixture with no white left. I like to use a knife, some prefer a spoon.
6. Scoop silicone into casting box. I say scoop because this material does not pour like molding silicone.  If you're trying to make a two part mold, you're going to have to add pressure to fill in the gaps.
7. Cure times depend on heat and moisture, but is generally 2-4 hours.

That's all there is to it! Follow the directions of some of the other casting instructables, and you should have a mold that you can make your own things with.
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crashaire3 years ago
Does anyone know if you could use these molds with plaster? for example if I was to make a mold of a sea shell and fill it with plaster for a plaster sea shell would that come out okay, or detailed enough, or is a shell too porous and/or the mold would not get all the little lines on the shell?

Usually with things with a lot of detail you want to mix up a couple of thin batches first and brush it on with a chip brush to make sure to get into all the details. The more layers the more detail you will grab out of the finished item. Just thin the mix out with a little more spirits. Then go in with a thicker top coat. And let it dry some between layers so you don't mess up the layers before hand. And if molding larger objects be sure to add in a layer of cheesecloth or burlap to give the mold some added strength. Just lay down a layer of silicone and put the fabric pieces down and use a brush to press them into the silicone.

Lonecoon (author)  crashaire3 years ago
I've gotten enough detail out of this to recast 25mm figures that were out of print, so a seashell should be no problem. The plaster will snap out easily, as it's just silicone.
would the mold cure all the way if glycerine isn't added? provided more time is given?
i made two molds with what I had. The first one I used 1/2 cup clear silicone sealant, acrylic paint, and 1/2 shot glass of turpinoid, and 1/2 cup cornstarch. It worked great! after an hour it was cured. The second one I ran out of clear silicone so I used Sudbury Heavy Duty ELASTO Sealant. It is elastomer which I saw online was silicone. I used twice the turpinoid and less cornstarch. I eyeballed it which was a mistake. I used part of the resulting mixture as a second layer on the first successful mold and it cured fine. I used the rest of the second mixture on a different item and after 24 hours its still squishy and wet inside. why did it work as a second layer on the first mold but not at all on the second?
Excellent timing to see this one. Been trying to figure out a way to make a mold for a carbon fiber project I've had in mind.
sdomph2 years ago
Awesome! Thanks! Once the mold is set, is this able to handle heat, cold?? Can this be dishwasher safe and food safe? My intent for mold making is for decrative things around the home as well as for chocolates, cakes with fondont and for partys, to do ice, rice crispy treats, jell-o's and what ever else my brian has pop into it! Thank you for sharing!
Lonecoon (author)  sdomph2 years ago
I have no idea, as I've never tried. I can't say I'd recommend it, but I don't see why it wouldn't be food safe. Try it on relatives you don't like before serving it to party guests.
danzo3212 years ago
Other good sources of pigment are mineral color, which masons put in mortar.. OK, you don't want a 20-lb sack of color? Try the chalk powder meant to go in snap-string line which is sold in hardware stores and comes out of a ketchup type squeeze bottle. Art stores may also have powdered pigment so your casting can be an exact hue.
sdomph danzo3212 years ago
Can you use side walk chalk that is for kids? Also to make homemade chalk it's craft paint and grout powder. Can these be used?
jduffy542 years ago
If you use 1 part caulk, 1 part cornstarch, and 2 parts mineral spirits (it does NOT like mixing, use a dremel, drill, or something similar and a bent nail to mix it well), then it will pour like normal molding silicone. (it is a little thicker, though.
Happy2Think3 years ago
Thanks, this is a really nice instructable, I will try it
to cast some items, and I have a question
Can this mold be used to cast poliester resins on it?
tvane12253 years ago
How well does this process actually work. will the silicone dry all the way through even if it is thicker than 1/4 inches?
bac5123 years ago
what is the paint for?
Lonecoon (author)  bac5123 years ago
The paint is to ensure that you get a proper mixture of your ingredients. Without the paint, It's much harder to tell if everything is properly mixed.
bac512 Lonecoon3 years ago
so basically, it's just for coloring... when it's all a uniform color, you know it's mixed well?