Polyester resin is different from polyurethane resin. It’s a completely different product; the main difference being that polyester resin is clear. It also takes a lot longer to cure and cannot be removed from the mold until it is completely hard.

We use polyester resin to cast anime style jewels like those used on this Trinity Blood costume. It’s a much cheaper alternative to buying jewels at a craft store and you have more options as far as color, size, and shape. The only limiter is that you need an appropriate mold.

So to get started casting, you’ll need some supplies.

Polyester resin is used by hobbyists to make paperweights so it’s fairly easy to find. You can get it at Michaels although we recommend you go with Tap Plastics as their product is better.

You’ll need catalyst. This is what you mix with the resin to make it harden. We also recommend getting the surface curing agent. The surface curing agent is pretty self explanatory: it helps to harden the outside of the cast resin jewels. We’re told you can do without it, but we always use it.

You’ll need dyes which you can get from Tap. Michaels used to carry them too but it doesn’t seem to be listed on their website anymore. The most important thing as far as dyes is to make sure it is specifically made for polyester resin.

And you’ll need molds. We use plastic paint trays for small jewels and we highly recommend buying the half-dome mold from Tap Plastics for big jewels. Just make sure the paint trays you buy are made from a thick plastic.

Lastly, you’ll need a scale to measure out the resin. The instructions for mixing the resin will tell you how many drops of catalyst and surface curing agent to add per ounce of resin. Eye-balling an ounce is kind of hard which is where the scale comes in.

Mixing the resin is really simple (on par with making Kraft macaroni and cheese). Just read the instructions, and mix up your resin, catalyst, curing agent and dye in a cup. Stir really well and then pour the resin into your molds. Polyester resin is very forgiving so you can be off by a couple drops here and there and it won’t matter.

After you pour the resin into the molds, you’ll want to leave it until it’s completely cured. This can take 4-6 hours depending on the temperature. The warmer it is, the faster the resin will cure.

Important safety note: the curing process for polyester resin generates a toxic fumes. Do not do this inside. Do it in your garage or out on your patio. Also curing resin is an exothermic reaction: it generates heat. Make sure your molds and whatever you’re resting your mold on can take heat.

When the resin is completely cured and hard, you can just flex the mold or tap it gently on a table to pop the jewels out. The finishing touch is gluing the resin jewel to kitchen foil to make it shine. You can skip this step but we find the jewels look a lot prettier if they’re shiny.

For gluing the jewels to fabric, we use E6000 which is available at Home Depot or Michaels or JoAnns. (It’s cheaper at Home Depot.) For gluing jewels to hard surfaces like armor, we use quick setting epoxy which is available at the same places as E6000.

And that’s all there is to it!

As always, feel free to ask us questions if we missed anything.

Polyester Resin Casting FAQ

– Can I use a silicone mold to cast polyester resin?
We’ve been told by Tap that they now have a mold material suitable for casting polyester resin in. We haven’t tried it ourselves but if you contact them and ask, they’ll be able to tell you which product to use.  (And let us know how it goes!)

If you find that your gems are still curing tacky, you can also try a resin finishing spray to harden the surface. Thanks to Amethyst Angel for the tip!

– I found these awesome plastic molds at Michaels used for soaps. Can I use them as molds?
Unfortunately no. Those soap molds are for cold-pour soaps and the plastic is very thin. It will melt under high temperatures and since curing resin generates quite a bit of heat…
– But you said I could use plastic paint trays!
Yes we did. Plastic paint trays tend to be made from much thicker plastic. If it’s made from thinner plastic, you can’t use it for the same reason you can’t use soap molds. Of course, you are welcome to try it… but just so you know, we’ve destroyed quite a few soap molds which is why we’re pretty sure it won’t work. =)
– Can I use baking tins as molds?
We’ve gotten asked this a couple times and we’ve never tried it ourselves but we heard from someone that they used muffin trays and it worked just fine. Thanks for the tip Shoebox! (If you have problems with the gem sticking, try adding a mold release.)