Making a rubber mold is easy and can help you reproduce something from nature or man-made. Using a two-part RTV rubber is a fun way to begin a new hobby and can open up a world of craft possibilities.
Find something that you wish to mold Could be a pine cone that you wish to make into candles, an animal that you’ve sculpted and want to duplicate to give as a gift, anything that you want.
Look for mold making material. There are a number of companies that sell rubber for making molds. Type “mold making materials” into Google for a list of suppliers.
Build your mold box. You will need to surround your model with some sort of wall to contain the liquid mold rubber. Generally you should leave 1/2″ between the walls and your model, use a yogurt container, or make a custom form out of foam core and hot melt glue.
Determine if you need to seal model. In order to make sure your model will release from the mold rubber you must first seal your model if it is porous, and you may also need to apply a release agent. If your model is made of wood, plaster, unglazed ceramic, stone, concrete etc. it is porous and needs to be sealed with Krylon clear acrylic spray or with a sealer available from the mold rubber supplier.
Apply proper release agent. If you are using a urethane mold rubber and your model is anything other than silicone, you will need to apply a silicone based release agent. If you are using a silicone mold rubber and your model is anything other than silicone, you do not need a release agent. If you are using silicone mold rubber and your model is made of silicone you need to use a non-silicone based release agent.
Mix and pour your mold rubber. There should be instructions with the material. Be sure to mix both sides first before measuring out how much you need, (Some suppliers have tools to estimate how much you will need.) Thoroughly mix both sides together and pour at the bottom next to your model. Don’t pour directly onto your model or you may trap air and lose surface detail in the mold.
Demold. After waiting the proper time, usually overnight, poke the rubber to make sure it is fully cured and not sticky. Remove the walls of your mold box first, using a razor blade if necessary. Hopefully you will now be able to push with your thumbs down in the center to break the air seal and remove your model from the mold rubber. Depending on your model you may have to use a sharp knife to create a seam and cut the rubber to release it.
Inspect. You are done! Congratulations you have just made your first mold. Visually inspect the inside to verify that it captured all the detail you wanted. If you find imperfections make a note so that you can correct it in the future. You are now ready to cast anything you like! Try Plastic, plaster, Ice (Water swells when it freezes), chocolate (some mold rubber is food safe, most are not) jell-o, wax, Foam, etc.