Intro to Basic Resin Casting

resin armor

finished resin pieces and some components

One of the major challenges I faced when I was just getting started in crafting props and accessories was making the massive leap from cutting and gluing things (simple skills we began learning in kindergarten) to working with new materials like resin, plastic and various rubber compounds (which had more in common with an undergraduate chemistry class).

Granted, back when I started cosplaying, YouTube hadn’t yet been invented, and online tutorials were few and far between… (We also had to walk uphill both ways to buy thread. In the snow. Barefoot. Now get off my lawn.) That meant when I wanted to learn how to work with resin, I just bought a can and began experimenting – and while I did learn quite a bit, that trial-and-error process took its toll on my house (and probably a few brain cells, as I unknowingly purchased one of the more toxic varieties).

Fortunately, there’s now a wealth of information out there to help beginners select and approach new materials! Still, it can be daunting to take a step into working with toxic chemicals – and rightly so, as misuse can cause serious damage to your health or property. Even though I read instructions and do my research, I personally still find it helpful to watch someone experienced work with a material before I try it myself.

With that in mind, I’ve documented one of my projects and created a simple walkthrough to show, step-by-step, how I use resin to make small costume accessories. All the techniques shown here are beginner-friendly, especially if you’re starting with a fairly simple design. (If you’re looking for more advanced techniques, head over to Smooth-On‘s website and watch their product videos. Or troll that newfangled YouTube thing.) ^_^

(Links throughout are provided only for example; I recommend shopping around for the best price and availability.)

Choosing A Resin

There are several types of liquid resin. I won’t cover them all here, partly because I don’t want this to be a thirty-page tutorial and partly because I only have personal experience with about four or five types. Here’s a super-brief overview of the most common varieties, based on my own experience working with it (so should not be taken as proven fact; read the labels on your materials!):

Polyester resin is usually the cheapest and easiest to find at craft stores, but has the vilest odor of the three. You don’t want to pour it in your living space, because the fumes will do very bad things to you (though ALL resin requires proper ventilation; keep fans running and windows open, or pour outdoors when possible). Most craft-store polyester resin requires you to mix in a concentrated catalyst, which on its own is highly toxic and caustic. On the plus side, polyester resin is fairly forgiving about mix ratios, and you don’t need a gram scale or specialized equipment to cast it. I’ve also found it’s the least likely to trap air bubbles, so it’s good for gemstones or transparent objects.

Epoxy resin has a lower viscosity and is much lower-odor than polyester resin. It comes in both A-B mixtures and catalyst formulas, and what I like about the type I use (EnviroTex) is that it sets up fairly quickly, but doesn’t fully harden for about 48 hours. This means you can bend half-cured pieces to make curved shapes. (I’ll be doing this later in this demo.) Epoxy resin is less forgiving than polyester in terms of getting your proportions exactly accurate, though, so you want to make sure you measure carefully.

Urethane resin has the least odor and cures more quickly, but is also the most expensive. Also, a vacuum pump, pressure-casting or a vibrating platform is recommended if you’re casting transparent pieces, as in my experience it seems to trap more air bubbles than the other varieties.

Choosing A Mold

Slayers

Resin can only produce objects as good as the mold it is poured into. Molds for some shapes can be easy to find. You can buy commercial ones, or look for objects around the house –- for example, nearly all of the jewels for our Slayers costumes (at right) were cast in inexpensive molded plastic objects such as measuring spoons, a paint palette, or the shell of an inverted tap-light.

Molds must be rigid enough to retain their shape when filled with liquid, but flexible enough that you can bend them slightly to pop the hardened resin out. For a comparison, think of plastic or silicone ice cube trays or chocolate molds. (By the way, you can cast resin in those, too! Just… not the same ones you use for food. Please.)

Note: If you’re using a prefab or found-item mold, you can skip down to the “Prepping the Mold” section, as the next bit is about making your own molds.

Making An Original

If you need a specific design for your costume, you may have to find or create an original piece and make a mold of it. Resin can be very useful for replicating a handcrafted object down to the precise details, especially if you want to produce multiple identical objects.

originalIn this example, I’m going to cast an armored hand plate. For this costume set I need four identical plates, so rather than hand-craft them all and attempt to match the details exactly, I’ll make just one original, then use that to make a mold. I’m using Super Sculpey and half-round scrapbooking pearls to make this particular piece.

If you’re using a substance like polymer clay, make sure it is completely finished — baked, sanded, textured, whatever else you may want to do with it — before moving on to moldmaking. Even small flaws like fingerprints can reproduce in a resin cast, and it’s much easier to eliminate those from the original than it is to try to polish them out of each replica you make.

Note: In general, whatever you’re using to make your original should be a nonporous material. If you’re using a porous or semiporous material (fabric, wood, Paperclay, et al.), you will likely need to coat it in sealer or varnish before making your mold. This will depend largely on what moldmaking material you choose, though; read the directions on your material to determine if it will work with your object.

Prepping Original For Molding

This step will also vary dramatically depending on what moldmaking material you use. If your mold material is a putty type (Alumilite) or a paste (liquid latex), you probably won’t need to put the pieces inside a box. If you’re using any sort of fluid material such as silicone or urethane, however, you’ll need some means of containing the material in its liquid form.

Since I’ll be using silicone to make my mold, I’m using a plastic food container with raised edges. The piece is small and flat enough that I can place it on the bottom of the container and pour over it. (For larger pieces, I might have to construct a larger container to fit around my object.) Food containers such as carryout boxes, plastic plate lids and disposable cups are great moldmaking resources. For very small pieces, I cut paper cups in half and glue them edge-down on a piece of aluminum foil on a tray. Don’t spend any extra money on this step; recycle your trash instead!

glued
Because I need my piece flush to the “floor” of the box and don’t want any of the silicone seeping beneath it, I’ll use hot glue all around the edges of the back of the piece and glue it down flat. I have some extra room in this box, and I don’t want to waste expensive silicone, so I also add a couple of small armor plates that I need to cast to utilize the extra space. (If I didn’t have these, I would use some foil or cardboard to block off that part of the box to avoid filling it with silicone, or use a smaller box.)

Note: It should go without saying that you should NOT use the same containers for moldmaking and food storage. Plastic food boxes are three for a dollar at the dollar store. Go buy some specifically for your cosplay hobby, and don’t risk poisoning yourself.

Pouring the Mold

The silicone I’m using is Dragon Skin 30 from Smooth-On. As a platinum-cure silicone, it’s not cheap, but I like working with it (and also casting things from it, but we’ll save that for a different tutorial!). For less expensive options (also in smaller quantities), you can try tin-cure silicone, urethane, silicone putty, or liquid latex (though I’ve never had much luck with latex molds, as they seem to distort and lose detail fairly quickly). Read the directions for your material of choice, as each of these uses a different process!

pouring dragon skin
Dragon Skin is an A-B compound; it comes in two parts, of which you measure equal amounts and mix together. I use disposable paper cups to measure each part, then combine them into another container for mixing. This is not only for ease of measuring, but also for cleanup. It’s very difficult to clean part A or part B individually, since they are very gooey and resist washing, but once they’re mixed together, they cure into a dry, stretchy rubber. This means the individual measuring cups can’t be cleaned, but it’s easy to clean out the larger mixing bowl later; you just peel the layer of rubber off the glass in one piece!

mineral spirits

I’m using a high-viscosity silicone, but I want it to pick up the fine detail from my object, so I add a small amount of mineral spirits to thin it. (Using a lower-viscosity version like Dragon Skin 20 would eliminate the need for this step, but I have Dragon Skin 30 left over from a previous project. If you’re buying something specifically to make molds, you’ll probably want to go with one of the MoldMax products, so you won’t need to worry about this.)

mixing

When mixing any A-B compound, you want to stir aggressively for at least 30 seconds (longer for large quantities), scrape the sides and bottom of the container, and repeatedly scrape off the mixing stick against the edge of the cup to make sure all the material is mixed in. If there are areas of material that don’t get mixed properly, it could ruin your mold or make it sticky.

pouring dragonskin

Once the silicone is mixed, I pour a little of it into the mold. When pouring, always start from the lowest point of the mold; that way, air is pushed up and out as the box fills, rather than being trapped in bubbles at the bottom (bubbles can ruin your mold, as they’ll add unsightly tumors to the object you’re casting).

brushing
Since my object has a lot of detail, I use a paintbrush to push silicone down into all the depressions and make sure there aren’t any air bubbles lurking in the recesses of the design. Once the surface is completely covered, I pour the rest of the silicone in and let it settle. It’s often a good idea to tap the sides of the box or the table surface to shake additional bubbles to the top. (Or you can set your phone to vibrate, balance the box on it, and call it repeatedly… but I’m not responsible for any damage to personal electronics due to, say, being covered in liquid rubber.) ^_^

setting

Make sure your mold is sitting on a completely level surface while it cures. Since you’ll be flipping the mold over to cast the resin, you want the surface to be perfectly horizontal.

peeling moldmold

Removing the Mold

I let the mold cure overnight (read the directions on your material to know how long it must sit before demolding). When I’m ready to pull the mold, I start by loosening the block of rubber with a butter knife around the edges of the box. Silicone is pretty forgiving, so I’m not too worried about damaging it (but don’t force it). When I have a corner of the rubber free, I can just pull it gently out of the box, and presto! My original design is perfectly replicated in negative, ready for casting.

If your originals pop off and get stuck in the rubber, no worries; just ease one corner free and pull the rubber back gently until your original comes out. (If the rubber has soaked in or adhered to your original, it’s possible that your material was too porous or wasn’t sealed well enough.)

Preparing the Mold

powdering moldMany molds will need some sort of release agent applied to ensure that the resin does not adhere to the mold itself. You have a few options here: You can use a commercial release agent; you can make your own out of a spray solution of dish soap and alcohol; or you can use a coating of fine powder to line the mold. This third option is not viable for transparent casts, as the powder becomes embedded in the plastic, but it’s great if you happen to want your cast to have a colored finish!

I use a paintbrush to smooth a layer of super-fine metallic powder all over the inside of the mold (in this case, mixing silver and gold in different areas). It’s important not to have too much, as a heavy buildup of powder can create pits in the surface of the cast. The powder sticks to the silicone, so I blow gently on the mold when I’m done to clear away any excess powder.

You can purchase commercial resin powders, which are actually finely-ground bits of metal and tend to be quite costly, or you can use extra-fine craft glitter or any pigmented powder for a cheaper option. I’m particularly fond of theatrical makeup pigments and powders, which are not as cheap but go a long way.

Mixing the Resin

For this project, I’m using EnviroTex Lite epoxy resin. The formula requires mixing equal parts A and B, so I use graduated measuring cups to pour each part.
measuring resin

Note: I’m a big fan of reusing and recycling and saving money where I can, so I save things like liquid laundry detergent caps and plastic yogurt cups, wash them out, and use them for mixing resin. These graduated measuring cups came with a laundry detergent bottle over a year ago, and I’m still using them. Just clean out the uncured resin with a cotton ball soaked in acetone (nail polish remover) after each use, and you can reuse your cups indefinitely.

combining resin

Once you’ve measured your resin, combine the parts in a mixing container. Stir thoroughly, scraping sides and bottom, until resin is fully mixed. (I use wooden craft sticks, also known as Popsicle sticks, for this. They’re available by the hundred at craft stores.)
pouring resinPour the liquid resin into the mold, starting at the lowest point. Fill it 2/3 of the way, let the resin spread out, and then add a little at a time to avoid overfilling the mold.

bubble fishing

If your mold has undercut or recessed areas (such as the little dots across the edge of my piece), use a toothpick or pointed object to fish out any air bubbles that may have been trapped inside them. You may also want to tap on the table or blow gently over the surface of the resin to loosen any remaining bubbles trapped in the resin.

armor plates

I try to measure my resin accurately, but in case I overestimate the volume of the mold, I like to keep several extra molds lying around so I don’t end up wasting any resin. In this case, I have more small armor plates to cast, so I’ll pour the excess resin into those until I run out. If you don’t have any other molds prepared, pour surplus resin into a disposable container (Dixie cup, bottle cap, etc.) and let it harden before you throw it away. (If you throw it away in liquid form, resin WILL find a way to leak and permanently cement things to the inside of your garbage can.)

Bonus Step: Curving Pieces

curvedSo far as I can tell, this only works with certain kinds of epoxy resin, and your mileage may vary – but if you catch it in the right window, you can bend the mold while the piece is curing and get a flat piece to hold a curve. (Otherwise you have to make a curved mold and do slush casting, which is much more complicated and time-consuming.)

For the resin I’m using, the ideal window is between ten and twelve hours after pouring. That’s when the resin has set up so it’s solid to the touch, but isn’t yet hard. If I gently bend the mold and fix it in place, then leave it for the next 24 hours or so, the resin will finish curing in a curved shape. (If I miss that narrow window, the resin will still bend somewhat, but will revert to its flat form over time.)

I’ve tied the entire mold in place inside another curved piece so the plate has a slight curve and will fit comfortably over the back of my hand. I’ll leave it like this for another day.

Demolding

demolding

Once the resin is fully cured – which, depending on the kind of resin you use, can take anywhere from twelve hours to two days – it can be removed from the mold. If you prepared your mold with a release agent, this step is simply a matter of peeling the soft mold away from the cast, or flexing your rigid mold just enough to pop the resin piece out (just like a plastic ice tray).

(On the piece pictured, note that the flexible mold returns to flat, but the fully-cured resin piece retains its curve. SO much easier than slush casting in a curved mold!)

Once you’ve demolded the piece, you may need to trim or sand any irregularities along the edges. Then you’re ready to paint, drill, distress, glue or otherwise finish your piece.

resin armor…And voila! You have a custom-made hard plastic costume accessory. If you need more than one, just repeat the process as needed.

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9 Comments

  1. Hello. Excellent tutorial. I”m casting playing cards in polyester resin and am having a terrible time. pieces are coming out great but the resin is soaking into the edges of the cards. I got the suggestion to use Krylon Workable Fixative to coat the cards. Didn’t work. My fear is that any poly based spray is just going to break down in the resin. Any suggestions would be MUCH MUCH MUCH appreciated!

    I love how much thought you have put into this post!

    Thanks for sharing!!

  2. would this method allow for enough curving for pauldrons? Also what type of envirotex resin did you use? Thanks a bunch.

  3. Wow, very nice tutorial, thanks for that!
    I am from Germany, and the only way i could get smooth-on is via internet, which would be very very expensive due to the shipping, zoll and so on.
    (i don’t know whether i am allowed to post links, but…)
    if i had something like that: https://www.amazon.de/Epoxidharz-Epoxydharz-Epoxi-Laminierharz-Terra/dp/B019286D6A/ref=sr_1_1?ie=UTF8&qid=1482169381&sr=8-1&keywords=Epoxidharz,
    would it be possible to make entire pieces of armor (like your leg/ arm plates) out of it?
    Or do you think i need to get smooth-on?
    Thank you again 🙂

    • I’m not familiar with that brand, but assuming it’s a similar epoxy resin, it should work the same. However, I don’t recommend using resin for constructing body armor, because very large pieces don’t flex and can be extremely brittle. Resin works well for small detail pieces, but for leg armor, etc. I’d suggest using a more flexible material such as foam or thermoplastic.
      Alena recently posted…Product Review: FlexbondMy Profile

  4. When I cast or pour anything in resin I place it in or on top of an electric jewelry cleaner. It can then be turned on to vibrate on one of two speaks and all of those tiny little bubbles dissapear.

  5. Awesome tutorial.
    Can you give please ratios for homemade release agent and details of which alcohol?
    Warm regards from South Africa.

  6. I have a vibrator from a vintage water bed. Yah, the kind you used to see in flee-bag motels where you put a quarter in a box next to the bed and it starts vibrating. Attach the vibrator to a board or tray of some sort and plug into household current. Place your molds and poured resins (inside the mold) onto this board/tray for a few minutes until all the air bubbles rise to the top and then let it sit until cured. We also have a vacuum chamber to remove air bubbles, but we use that mainly for degassing silicone (it takes it down to 3 atmospheres).
    Not my video, but found this on the tube. https://www.google.com/search?q=degassing+silicone&oq=degassing+s&aqs=chrome.1.69i57j0l5.6453j0j7&sourceid=chrome&ie=UTF-8#kpvalbx=1

  7. Very good article .. well written .. easy to understand and follow directions .. you are a PRO .. well appreciated ..
    THANK YOU .. waiting for more

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