Most people opt to have a professional moldmaker and caster produce their piece, such as Randy Buckler at Resins By Randy, whose work is innovative and outstanding. But for those of us who want ultimate quality and production control, doing it at home is the inevitable option. This article is intended to give you some technical points and ideas on which to grow your own technique.

An overview of molds

The concept of a mold is very simple, but the execution of one is unfortunately not. Due to the nature of horse models, with their many varied shapes, surfaces, long thin legs poking out at odd angles, complex flying manes and pointy little ears, we have picked an inherently difficult object to duplicate easily. (If you want easy, sculpt apples and oranges.)

So what is a mold? In essence, negative space in the shape of your positive model. When material is poured into the negative space and hardens, the mold is pulled off and you have an exact duplicate of your original.

Though not absolutely 100% vital, the waste mold is an important midway step for most artists. Because it is sometimes difficult to achieve perfection in the soft clay, a hard resin casting is made from the original. In the resin, detail can be sanded and epoxied onto the model with a degree of precision sometimes impossible in clay. The production mold is then made from this perfected resin casting.

Another reason for a waste mold is that it’s almost impossible to get a good production mold from a soft clay model. More on this later, when you have a good idea about what the heck I’m talking about.

It’s an excellent idea at this point to draw your projected seams onto the model. This is where you will cut the mold open when you’re ready to take your horse out. Because most mold rubbers are opaque, it’s nice to cut down to a line and follow it without having to blindly visualize where you are.

Preparation includes applying a release agent to the model to minimize the chance that the rubber will somehow make a chemical bond with the clay. That would be the end of your horse as we know it!

Note that her stand is just a pencil jammed into the clay of her belly. Baaaaaaad idea! Do as I say, not as I do. Always have a good armature and connections.

The next step must be done with great care to minimize problems later on. At this point you will be very thankful that you spent so much time on your armature and wires-to-base connections because the model needs to be turned upside down, sideways and every which way. If you weren’t careful and snug with your armature, now is the time to cry, or do some major overhauling. You might end up with a vaguely horse-shaped clay pancake on the studio floor and slimy silicone rubber all over everything.

We use silicone because of its amazing tear strength (you can stretch it a LOT before it tears, which can be a useful attribute!), non-toxicity and stable chemical properties. Silicone is more expensive than other rubbers such as urethane and latex, but has some nice advantages for our type of molds. Though it is a more or less benign material, it is still a good idea to wear skin protection, a mask, and work in a well-ventilated area. Always take precautions when working with all this chemical stuff.

Most mold rubbers come in two separate containers, A and B. Depending on the type and brand, the liquid parts are mixed equally or by percentage, and by weight or volume.

The first coat of rubber is the most important. It must be put on thoroughly and carefully to minimize bubbles on the surface of the model. The horse should be rotated in all directions to allow the rubber to flow over the surface evenly. A small, stiff-bristled brush is handy for pushing rubber into the details. Just be careful not to push too hard and damage the clay. The detail coat should be allowed to set for the proper amount of time so it is not runny or sticky when you apply the second coat.

(As is often the case when working with unfamiliar materials, you may end up having to make a tool or two. In the lefthand illustration above, we are using a homemade brush that consists of a few bristles cut from a cheap paintbrush and held onto a Popsicle stick with tape. It allowed us to poke rubber into very tiny spaces, and it’s disposable!)

Silicone is an RTV rubber (Room Temperature Vulcanizing), which means it does not require extreme temperatures to set. If you want it to set faster, increase the room temperature or take it outside into the sun. (Only if it’s sunny, obviously.)

The number of coats that should be applied varies depending on the material you’re using and the specific model, but do make your coats thin and even. If you apply too much rubber at once it can be nasty. Keep the model rotating so the liquid rubber doesn’t droop and fall off!

Highland Heather took nine coats before we were satisfied. Your goal is to have a smooth outside of the blanket mold with no undercuts, so your mother mold (the outer shell that supports the inner mold and holds its shape) can release from it easily.

As the name implies, the mother mold goes all around the blanket mold, holding it together and acting as an exoskeleton. If your model is small like Heather, you might just want to use regular epoxy, which is a common item in most hobbyists’ households. For larger models it’s a money-saving measure to use a material like Freeman’s two-part 1010 Aluminum Epoxy Modelling Compound. I have no idea what application this stuff has in the real world, but it works great for mother molds. Definitely wear gloves, and work with it outside if possible! Foul-smelling substance.

Flatten out a well-mixed lump with a rolling pin until it is about 1/8 to 1/4 inch (3 to 6mm) thick, and lay it on one half of the blanket mold, pressing lightly so it follows the basic contours of the mold. After one side has set, apply Vaseline to the edges so the next application won’t bond to it, and repeat the same procedure on the other side. Now, once both halves have set, you have a rigid shell around your soft rubber that will hold it in place nicely. If you applied the epoxy right, it should pop off the inner mold in two halves, and will go back together snugly.

This is also a gut-wrenching procedure. When both the rubber blanket mold and epoxy mother mold have set (you should wait at least 24 hours to make sure), it’s time to remove the clay model so you can finally achieve that hard-won negative space we’ve been talking about.

It’s best to keep the mold in one or two pieces, but sometimes a complex model will require more cuts.

Of course, the faint of heart can always go home.