Resin 101: How to Cast Resin and Make a Custom Silicone Mold

Resin is a useful tool in cosplay, especially when you need to create multiple copies of one costume piece. A custom resin mold makes it easy for everything on the costume to look uniform.

You can easily purchase ready-made molds to use for resin casting, but some costumes will need their own specialized pieces. The good news is that making a custom silicone mold is not very difficult. It may seem a little intimidating if you’ve never used silicone or resin before, but all you really need to do is mix together the ingredients in a kit and wait for them to cure (or dry).

Once you get started casting your own resin in custom silicone molds, you’ll start to see how useful it can be, especially for intricate cosplay costumes. Instead of carving, molding, or gluing each piece individually, you can create it once (with clay for example) and just copy the rest, saving you so much time.

How to use resin

Resin is a liquid substance that you mix together and pour into a mold. After 1-2 days the liquid will solidify (or cure) to be a hard substance. In cosplay, you will most commonly see it referred to when people make jewels and gems. However, you can also use it to make a wide variety of other props and costume pieces. Some types of resin are clear and can be colored with translucent dyes, and other types that are opaque.

Resin also has a limited amount of time that you can work with before it begins the solidification process. You’ll want to be finished mixing and pouring the resin in this limited window of time. Usually, the resin will give you around 30 minutes of working time, but this will vary depending on the type of resin you purchase (it should be labeled on the bottle or directions your resin kit comes with). To make sure you’re using your time wisely, have all of your supplies ready to go before you start mixing the resin.

You also need to pay attention to the room temperature when working with resin. If the temperature is too cold, your resin creation will likely end up with bubbles trapped inside. In some cases, resin that is mixed in cold temperatures won’t be able to cure at all.

Ideally, you should work at a room temperature between 75ºF and 85ºF. At the very least keep the temperature above 65ºF, since the resin will not cure properly below this temperature. Working at lower temperatures (65º-75º) makes it more likely bubbles will form in your resin.

Supplies needed to work with resin:

• Epoxy resin
• Resin hardener (this usually comes packaged together with resin)
• A silicone mold or a plastic mold (silicone is easier to work with)
• Optional: Translucent resin dye (for colored gems)
• Optional: acrylic paint (for opaque coloring)
• Disposable gloves
• Beakers and stirring sticks

1. Mix equal amounts of resin and hardener in a beaker

In your resin kit, you should have two bottles of liquid substance. One is the resin, the other is the hardener. Take your beaker and pour in equal volumes of the substances. Being exact is important for helping the resin to harden correctly, so use the measurement lines on the beaker to help you pour the correct amounts.

It’s also a good idea to wear gloves for this whole process. While some resin brands are non-toxic, most can cause irritation and rashes if they come in contact with skin. Once the resin hardens, it’s no longer toxic. It’s just the liquid form that you have to be careful with.

After measuring the resin and hardener, mix the two substances slowly and carefully for about 5 minutes. Make sure to scrape the sides and bottom of the beaker so you get all the liquid incorporated. You’re finished mixing when no streaks or swirls are remaining in the mixture. 

Do not rush the mixing step. Aggressive stirring will cause extensive bubbles to form and they’ll be almost impossible to get rid of. Be patient and mix the two ingredients at a slow and steady pace.

2. Add color to the resin mixture

If you want your finished resin product to be colored, this is where you will add the dye. You do want to be careful not to add too much color since that can mess with the consistency of the resin mixture. But, a little color goes a long way with resin.

If you are using a clear resin, you may want to create something with transparent color. In this case, you will want to get translucent dye. You can find translucent dye specifically made for resin, or you can use drops of acrylic ink to color your resin.

If you don’t need a transparent color, you can also use acrylic paint. Add a little squeeze of the paint to your resin, and continue to carefully mix it until the paint is fully incorporated. The color that you see when mixing is usually pretty accurate to what you’ll get in the final product. It doesn’t cure to a lighter color like paint does.

If you want to have swirls of color instead of solid colored resin, you can add the paint or dye and mix it just a little before adding it to your resin mold.

3. Pour the resin into the mold

After you’re happy with the color of your resin, it’s time to pour it into the mold. This is another area where you may get bubbles if you are not careful. You want to try to pour slowly and carefully. Fill the mold to the very top, but avoid any overflow.

If you have a small or shallow mold, you can use a small scoop or even your mixing stick to pick up some of the resin mixture and put it into the mold. If you have a large mold, you can pour the resin mixture directly from the beaker. 

You want to pour the resin as close to the mold as you can get so that you don’t create air bubbles during this process. Hold the mold at a slight angle and start by pouring the resin onto the side of the large mold. As the mold fills up, you can move it back to an upright position so that you can fill it to the top.

4. Allow the resin to harden

After the mold is filled, you have a waiting game. Your resin kit should come with instructions that tell you how long it takes for the resin to cure. Usually, this will be 24-48 hours, but some products are quick-cure and will be ready sooner. As it hardens, you’ll want to keep the resin in a warm place (ideally 75ºF to 85ºF) to prevent air bubbles from getting trapped.

After the resin has fully cured, you can remove it from the mold and use it with whatever project you want. The resin will work with most types of glue, including hot glue. You can also drill holes in it to use the resin as beads.

Tips for getting better results with resin

• Place the bottles of resin and hardener in a warm bath for 30 minutes before starting. This is really only necessary if you’re working in a cooler than ideal environment. It will warm up the liquids so that they don’t bubble as much when you are mixing them together.
• Be slow and patient when stirring your resin. It’s so much easier to prevent bubbles from forming in the first place than to try to get rid of them after the fact.
• Wave a lighter under the mold and over the surface to help them rise to the top and pop. Do this after you’ve added your resin to the mold.
• Use a toothpick to pop large bubbles.
• You can use cooking and baking molds too. They don’t have to be molds that are specifically made for resin.
• A shiny mold will give you a shiny result, a dull mold will give you a dull finish. Keep that in mind when choosing the right mold for your project.
• Do not put leftover resin down the drain. It could potentially cause a severe blockage. Instead, let the resin cure in the beaker overnight, then throw away the beaker or remove the hardened resin and clean out the beaker for reuse.

How to cast your own silicone mold

A lot of the time, you can purchase ready-made silicone or plastic molds to use for your resin project. However, sometimes you won’t be able to find what you’re looking for, especially for cosplay where you often need something very specific. 

In these cases, you will need to cast your own silicone mold for your project. This is especially great if you have multiple pieces of your costume that need to look exactly the same. You can build the first one with clay, Worbla, EVA, etc., then create a silicone cast and create copies out of resin.

Supplies needed to make a silicone mold:

• An object to copy
• A non-silicone container that fits your object (or you can create your own, see step 1)
• A small digital scale
• A silicone mold kit (should include 2 parts)
• A beaker and stirring stick (do NOT use silicone beakers or stirring sticks)

1. Find or create a container for your mold

Before touching the silicone, you have to make sure you have a container ready to pour into. Just like with resin, liquid silicone can only be used for a short period of time before it starts to cure and harden. So you want to have everything ready to go first.

Find a container that is flat on the bottom. Place your object inside and make sure there is at least ¼ inch on all sides and enough vertical space to cover the object. If there is less than ¼ of space, you may risk ripping the mold as you remove your object later. If possible, try not to use a container that is too big. There’s nothing wrong with it, per se, but you’ll end up wasting a lot of silicone if you’re just trying to make a mold of a small object.

Do not use a silicone container (or a silicone object). The silicone casting material can be easily removed from almost any other material, but it will adhere to anything that is silicone, making the mold useless.

How to create a quick mold container

If you don’t have a ready-to-use container, you can make one for yourself pretty easily. 

1. Set up a perimeter for the mold. You can tape together cardboard in a square or use any other stiff material you have available. I have a set of old cookie cutters that I use. Make sure your perimeter is tall enough to fully cover your object with room to spare.
2. Place the perimeter on a piece of cardboard and glue it in place. Use hot glue on the inside and outside all along the bottom of the mold to prevent the silicone from leaking out. You’ll also want to use hot glue on any seams you created in the perimeter, such as the corners of a square.

2. Mix your silicone

With your silicone kit, you should have received two bottles of liquid substance that you need to mix together. You’ll want to add equal amounts of these and mix them. However, you should add equal amounts in weight, not volume. You should use a small kitchen scale to help you measure the two liquids correctly. After adding equal amounts, you’ll want to carefully stir the silicone mixture for 3-5 minutes until there are no streaks left.

Unlike resin, silicone is actually more likely to get bubbles when it’s warmer rather than cooler. For that reason, your working temperature can be less than it is when working with resin. Usually, around 70ºF will be fine, but be sure to check the recommendations of your specific silicone brand. 

Silicone also usually has a shorter working time than resin, some brands have a working time of as little as 5 minutes. So you want to be prepared to immediately add the silicone to the prepared container as soon as you’re finished mixing the two parts.

3. Pour your silicone until you cover your object completely

When you’ve fully mixed the silicone, all you have to do is pour it over the object that you’re making a mold from. Just like with resin, try to keep the tip of the beaker close to the container to avoid adding any bubbles to the mold. Cover the object completely with ¼ inch of silicone covering it in all directions (sides and on top).

4. Allow the silicone mold to cure

After you’ve added your silicone to the container, all you have to do is sit back and wait for it to cure. When it’s finished it should have a rubbery texture, but it should not feel sticky at all. If it feels sticky, that usually means it either needs a little longer to cure, or the two silicone parts were not correctly measured in equal amounts. 

Usually, the silicone will need to cure for 24-48 hours. Refer to the instructions in your kit to know what to expect for your specific brand. Temperature can also alter the amount of time it takes for the silicone mold to cure fully.

5. Trim the excess silicone

When it’s finished, you can remove the silicone mold from the container and pull the object out of the mold. You may have to use a small plastic knife around the edges of the container to help release it from sticking on the edges (like flipping a cake out of a tin after baking). 

Sometimes the mold will be absolutely perfect and there will be no further action required. However, there will often be some silicone that you’ll need to trim from the edges of the mold. This is just liquid that managed to get underneath your object as the silicone was curing. It looks a little sloppy, but it won’t affect the final look of any objects that you cast in resin.

Now you can use the molds with resin to create copies of your custom cosplay props and accessories.

Tips for getting a better silicone mold

• You can get rid of some bubbles by placing the mold in the refrigerator for an hour or so after pouring it into the mold. This gives the bubbles time to rise to the surface before the silicone starts to cure.
• Tape your object to the bottom of the container. Use tape to secure your object to the bottom of your container. This makes it less likely the silicone will leak under the object, making the last step easier.
• Use a paintbrush to get silicone in detailed pieces. Before pouring the silicone onto your piece, take an old paintbrush and paint a layer of the silicone onto the surface first. This will ensure that the silicone solution gets into all the nooks and crannies, giving you an exact copy.
• Sand your object before you make a mold. Your silicone mold will take on the exact surface characteristics of your original piece, so if you want a smooth surface, you’ll need to sand and polish the object you are copying.