Before making a tutorial, I’ve usually completed the project successfully a few times and know how to add my own pointers to help you get an extra-nice result.
Not this time, friends.
The sequence captured in these photos didn’t quite work out the way I needed it to, but I decided to go ahead and share my process because I think it would have worked for most purposes, and would probably have worked for my project (resin molding) if I’d had a bit more patience during the curing process.
Making Your Own Silicone Mold
Any silicone caulk labeled “100% silicone,” will work to create a mold for small to medium-sized objects- capturing detail in a reusable, easy to clean, flexible mold.
The problem? Pure silicone caulk is very thick and very goopy. This consistency makes it really hard to cast a mold without any bubbles or gaps in the silicone- Imagine trying to cast a mold in peanut butter and you’ll get the idea. This texture creates gaps and bubbles in the mold which leave ugly blister-like marks on the surface of cast objects when unmolded.
Solution: The internet-delivered several solutions for me: silicone caulk can be mixed with other ingredients to change the consistency without affecting the usability of the mold you make.
Here’s my tutorial and recipe for creating this quick-dry, smooth-consistency DIY silicone mold making material.
What You’ll Need:
- Disposable food prep gloves– keep this off your skin!
- well ventilated work area (i.e. outdoors, this will give off a caustic odor)
- Acrylic paint (craft grade acrylic paint is fine and may actually work better because of the high water content)
- Sturdy freezer-type gallon-sized ziplock bags
- 100% Silicone Caulk (If you’re making a larger mold and buying contractor-sized silicone tubes, you’ll also need a caulking gun)
- Wood craft sticks
Step 1: Add Paint (Catalyst + Pigment) to Mixing Bag
Begin by placing a generous amount of acrylic paint into the heavy-duty zip bag. There’s no hard and fast recipe, so let’s say begin with “one part” paint (to scale up or down, just consider “part” a smaller or larger unit of measurement, i.e. teaspoon, tablespoon, cup, pint)
I add paint for two reasons: 1. added pigment makes it easier to visually gauge when the mold material is mixed and ready to pour, and makes it easier to get a sense of the thickness of the silicone in a particular area of the mold. 2. Normally, silicone is catalyzed to cure via exposure to moisture in the air. The addition of craft paint integrates moisture directly into the mix, which means your silicone mold will cure as quickly as one hour, instead of the 24 hours normally needed for pure silicone.
Step 2. Silicone
Add 8 parts 100% silicone caulk to mixing bag. Roll back the zipper-portion of the bag to help keep the seal clean.
Step 3. Turpentine as Thinner
Working outside or in a very well-ventilated area, and with a helper holding the bag (or using a sturdy prop and clip to hold it upright) add 2 parts turpentine to your mixture in the bag.
Step 4. Mix
With paint, silicone, and turpentine added, seal your bag and gentle squeezing to mix the materials. Keep your gloves on for this part, and work in a protected and well-ventilated area, even heavy-duty bags can manage to leak!
The addition of paint also helps you track how well mixed your DIY silicone mold mixture is:
Step 5. Cut Bag
When you are ready to make your mold, snip off the tip of one corner of the bag.
Step 6. Make Mold!
You can now use the heavy duty zip bag as a piping bag. This will help you apply your silicone precisely to the item you are casting a mold of.
In this image, I’m preparing to create a mold of a small polymer clay sculpture of an ocean wave so I can then reproduce the wave in clear epoxy resin.
Using the thinned down silicone and the finer-tip application of the mixing bag turned piping bag, I can carefully apply the silicone to delicate detail and fragile areas of my item to be molded.
Carefully cover all surfaces and smooth to create a mold. You’ll want to carefully check for gaps in silicone (a bright contrasting color makes this easy!) so when you later pour your material to be molded it won’t leak out.
Step 7. Cure.
Allow to fully cure. Depending on humidity, the thickness of cast, and ingredient levels this may take anywhere from 1 hour to 1 day. When you can gently touch the surface and it firmly bounces back to touch without any hint of stickiness, you’re ready to unmold your cast object.
Where I Went Wrong: After a few previous successful test casts using this method, this time (while shooting the photos above) I didn’t end up with a usable mold. Here’s where I think I went wrong:
First, the polymer clay I used to create my sculpture was about 10 years old and either not fully fired in my oven or simply crumbly from age (and the additives used to reconstitute it after so many years), so upon unfolding, it disintegrated leaving countless particles stuck inside the mold.
Second, I expect there was some kind of unanticipated chemical reaction between the polymer, silicone, and epoxy resin. Each batch of resin cast in this mold emerged yellowed, sticky, and unusable. In the past, I HAVE successfully cast epoxy resin in silicone molds made with this recipe, so I’m blaming the polymer clay for this result.
A quick tip for easy unmolding of your art:
You’ll need (for casting objects)
paper coffee filter or folded paper towel
For easier uncasting of objects, begin by mixing 2-3 drops of dish soap in 2-3 tablespoons of water and mix thoroughly. Paint this mixture onto the object to be cast with a clean paintbrush. Allow to dry. Once dry, the surface should have a slightly textured, tacky surface feel. (if it doesn’t, apply another coat of soapy water and let dry).
Place 1-2 tablespoons of cornstarch into a porous package (a folded paper towel or coffee filter, etc) and pat the package of cornstarch against the surface of the object. This should create a very light and even dusting of cornstarch across the surface, making it easy to unmold your project when the silicone dries.