Before making a tutorial, I’ve usually completed the project successfully a few times and know how to add my own pointers to the tutorial to help you get an extra-nice result.

Not so much 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 needs (resin molding) if I’d had a bit more patience during the curing process.

Making Your Own Silicone Mold

Any 100% silicone caulk, available for purchase from any hardware or big box store, 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- these gaps and bubbles leave ugly blister-like marks on the surface of your 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 for creating this quick-dry, smooth consistency DIY silicone mold recipe.

What You’ll Need:

coated work gloves (nitrile examination gloves- keep this off your skin!)
well ventilated work area (i.e. outdoors, this will give off a caustic odor)
turpentine
acrylic paint (craft grade paint is fine)
heavy duty zip locs
scissors
caulk & caulking gun
wood craft sticks

 

Step 1.

Begin by placing a healthy 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. the addition of pigment makes the silicone easier to see and makes it easier to visually gauge the thickness of silicone in a particular area of the mold. 2. Silicone is catalyzed to cure via exposure to moisture in the air. The addition of craft paint integrates some moisture into the mix, which means your silicone could cure within one hour, instead of 24 hours.

Step 2.

Add 8 parts 100% silicone caulk to mixing bag.

 

Step 3.

Working outside or in a very well-ventilated area, With a helper holding the bag, or using a cup to prop it upright, add 2 parts turpentine to your mixture in the bag.

 

 

Step 4.

Seal your bag and begin to squeeze to mix. (Keep your gloves on for this part, as 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:

 

mixing…

almost mixed…

 

well mixed! 

 

Step 5.

When you are ready to make your mold, squeeze the mold making material back from one corner and snip off just the tip of the corner of the bag.

 

Step 6.

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 mold.

 

Step 6.

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.

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 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 unmolding it disintigrated leaving counless particles stick inside the mold.

Second, 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. I’m blaming the polymer clay for this result, as previously I’ve had a perfect score using this exact recipe to create molds of polymer-clay-sculpted items that were fully cured and coated with an laquered finish.

 


A quick tip for easy unmolding of your art:

You’ll need (for casting objects)
dish soap
water
cornstarch
paintbrush
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 super-easy to unmold your project when the silicone dries without lots of cornstarch left behind.

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