The Easiest Possible Mold-Making and Casting for Resin Art Toys
Intro:
While taking Ben Light’s Art Toys I became very interested in making resin figures using a molding and casting process… despite the fact that the shop at ITP isn’t really designed to support this toy-making method. As a result, I had to do a lot of my own research and material gathering in order to do it, and so I decided to gather all of that info in one place as an ad-hoc tutorial in case anyone is interested in doing something similar in the future.
I would like to start out by saying that this mold-making process would work with all sorts of objects whether it be an existing action figure, something kit-bashed, a hand-sculpted piece or something 3D printed. However, I will not be going into any of these processes in this tutorial. Really the only note in that regard I will mention is that ideally, the object you are casting is non-porous, so something made out of wood, for example, would likely do best with some sort of sealant coat.
Also, much of the information I have aggregated here has come from various online tutorials, with this one being my favorite if you want to go straight to the source. However, there are bits and pieces of information included in this document that I had to learn for myself the hard way too.
One or Two-Part Mold?
When making a mold of some sort of figure, you have the option of either a one-part or two-part mold. One-part molds are easier to make, but can get messed up or torn if you are attempting to make a one-part mold of an object with many appendages or overhangs. I will get to that more later. Two-part molds are more time consuming to make and a bit more finicky to cast with, but are much easier to de-mold, especially with more complex shapes. There are countless wonderful tutorials online for making two-part molds that I would recommend looking up if you are leaning that way, but if you want the absolute simplest (but potentially not most perfect) mold making strategy then you are in the right place.
One Part Mold:
Materials:
Foamcore (or a similar stiff, easily cuttable material)
Hot glue gun
(Optional) Paper Towel/Toilet Paper roll or dixie cups
(Optional) Chop Sticks or wooden grill skewer sticks
Exacto knife, box cutter etc
Smooth-On OOMOO silicone
Smooth-On Smooth-Cast resin
Various sizes of disposable Cups/containers (for mixing silicone and resin)
Disposable stirring appendages (tongue depressors, disposable spoons, etc)
(Optional) Ease Release 200 Mold Release
(Optional) Resin color pigment dye or powder
Rubber bands or tape
First things first, if your figures/objects have extremities that stick out, in order to ensure that you can easily de-mold your figure, you might actually want to remove the arms and made separate molds for each arm in addition to the torso/legs. (you would then reattach them once you have cast them in resin) For something the size of an action figure arm, you can simply make the mold in a dixie cup like I did, or even in a piece of a toilet paper roll hot glued down to mat board or acrylic. Then, for the main body, I built a box with foam core and hot glue that would fit around my figure with a minimum of about half an inch clearance on all sides. In my photos, you can see that I glued the figure into this box upside down. Don't do this, it was dumb. Instead, glue the feet to the bottom of the box. The reason to do this is that this way the bottom of the feet will be exposed when the mold dries. This way, when you then go to pour your resin into the mold, you will have an easy place to pour it in through the feet, and the only part of the original figure that won’t be cast accurately will be the bottom of the feet.
Adding Vents:
In addition to my reasoning above, the reason I removed the arms from the body before casting is to reduce the problem of air pockets during the casting process. When you pour your resin into the mold, air can (and will) get trapped in areas where it does not have a place to escape upwards and out of the mold. This usually occurs in places where appendages stick out to the side from the center area in which you are pouring. So, if you can’t or don’t want to remove your figure’s appendages, you can instead make vents. What this essentially does is add a hole for air to flow up and out from all the highest places in your mold that do not have a direct connection to the topmost part of your mold. Using cut up chopsticks or grilling skewers, hot glue them to the appendages that stick out so that the vents are parallel to where you plan on pouring your resin into the mold. Once you cast it, this will create a hole to the surface that will allow air to escape and resin to fill all parts of your mold. This description is a bit confusing, but take a look at these pictures to get a better idea of what I mean.
Finally, an optional additional material to use here is an aerosol mold release agent. Applying this to your figure as suggested on the can will allow it to be removed much more easily from your silicone. However, as I said, this is optional because silicone specifically does not aggressively stick to any other material besides itself.
Choosing a Silicone:
The next step is pouring the silicone that forms the mold. I have only ever used Smooth-On silicone, and it has always worked wonderfully. I would highly recommend the OOMOO 25 or OOMOO 30 silicone ( I have only ever purchased the Trial Size because I never need more than that). OOMOO is not the most robust of the silicones made by Smooth-On, but importantly, for us student makers, it doesn’t require you to use a vacuum degasser OR electronic scale in order to mix and cast it. It’s also the cheapest silicone from Smooth-On. You can get Smooth-On products at Blick or on Amazon, but if you want to support an amazing local business (or have questions about anything related to casting) I would highly recommend checking out The Compleat Sculptor in Chelsea. They are a huge store full of literally everything you could ever want for your art projects, and the employees are incredibly friendly and helpful (and they have an adorable shop cat!).
Pouring the Silicone:
Once you have your silicone, simply follow the directions included. If you chose OOMOO, it will be a one to one mixture, so just fill two identical containers to the same level before mixing them together. A couple of notes about this stage:
- Take a look at this calculator on Smooth-On’s website to determine how much silicone you will need. I have found that I always end up using more than I estimated by eye, so it is worth doing at least a preliminary calculation using their tool.
- Because you are not using a vacuum degasser to remove air bubbles from your silicone, you have to do your best to make sure you avoid introducing them into your mold. This is done by mixing the silicone firmly but not too vigorously as well as pouring the mixed silicone from high up, in a thin stream into the lowest part of the mold container and allowing it to fill up from the bottom. Once you have filled the container you can also tap the sides of the mold, or tap the mold on the table to help the remaining air bubbles to rise to the surface.
Removing the Original from the Mold:
Once your silicone has dried, you now have to remove your figure. First, remove the side of your box, ideally without ripping the sides themselves (you will need two of them later). This is the part where having a two-part mold is much cleaner and more simple. With a one-part mold, you essentially have to use an Exacto knife to cut your figure out of the mold. When you do this, try to make just one long cut that traces up one side of your figure, over its head, and down the other side. However, when you do this, try to avoid making a straight cut — instead try to make your cut wavy; this way the two sides of the mold will lock back into place when you fill the mold and won't slide around. Ideally, you will be able to keep your mold in one piece when cutting out your figure, but it is inevitable that your cut will get a bit messy. This is the reason this type of mold is not ideal — because ultimately the integrity of your mold is only as good as how clean your cut to remove the figure was.
Prepping to Pour Your First Cast:
Now that your mold is empty and ready to cast, start by applying a coat of mold release to the inside of your mold if you have it. It is also optional for this stage as well, but what it does is make removing your resin figure easier and allows the mold to last longer before breaking down. Taking two of the sides of your box from when you made your mold, place them on either side of your mold and then wrap it with tape, rubber bands, string — anything like that which will slightly squeeze the mold and keep the seam you cut to remove your figure tightly sealed.
Choosing a Resin:
Like with the silicone, I have only ever worked with Smooth-On Resin, but this is because it seems to be the most accessible, largely the cheapest, and the industry standard. Searching “casting resin” on Amazon returns many many results but, importantly, the resin we will be using from Smooth-On is a urethane resin, not an epoxy resin. This makes it possible to work without needing a scale, is better suited for figure detailing and coloring, and works much better when poured in thick shapes. The specific type of resin is called Smooth-Cast and it is worth taking a look at their list of products to get a sense of what you need for your project. If you want white or black resin those each have different number codes (I would suggest against clear resin simply because without a vacuum chamber the inevitable air bubbles will be very visible inside and your figure will not be crystal clear), and I have always used Smooth-Cast 325 because it is specifically designed to take color pigment really well. This way I have been able to cast figures with really rich colors simply by adding my own resin pigment, though it is, unfortunately, one additional thing that must be purchased.
One note: While I have yet to try this, I plan on switching to Smooth-Cast 326 or 327 when my current supply runs out, so it may be worth looking into those instead. The reason is, the higher the number, the longer the material takes to cure. 325 takes only a few minutes to cure, meaning you have to work with it really fast, or else it hardens before you can pour it in the mold. It also means there is less time for air bubbles to escape which can cause imperfections in your final figure if you are not careful.
Pouring the Resin:
Because Smooth-Cast uses a one-to-one ratio like OOMOO, the process of preparing your materials is very similar. Mix each component separately without introducing too many air bubbles, and pour them into separate identical cups. If you are adding color, make sure to add it to one of your components before mixing them — this allows you time to get the color right without worrying about your mixture hardening. Then quickly but gently mix your two parts together. Pour a small amount into your mold and then swirl the mold around to allow air bubbles in the bottom to escape and the resin to coat all parts of the inside of the mold. You can repeat this process a couple of times as you slowly fill the mold, just make sure to keep in mind you only have so much time before the resin becomes too hard to work with. Overfill your mold to make sure as air escapes the mold does not become underfilled. Tapping the mold on the table and slightly squeezing it once it is filled is another way to help air bubbles escape. (They really are the biggest enemy of casters like myself who work without a vacuum chamber). And then you wait, and hope that most of the air has escaped!
Finishing Up:
As much as I hate to admit it, Ben Light’s adage about making a series of objects applies to this process as well: like pancakes, the first cast will basically always be an imperfect throwaway. Luckily, casting figures uses relatively little material, so you should have plenty of your Smooth-Cast left to try a few more times. Once you have a figure that came out well, the final step is cleaning up your cast. When it comes out of the mold there will inevitably be excess resin attached, so just take a straight edge or Exacto knife and carefully trim it. Depending on how much excess there is where you poured the resin into the mold, you may also need to do some sanding, or use a Dremel to remove it. And then it is just up to you if you want to leave it bare or move on to painting your new figure!
