With epoxy some things are hard to sculpt - like ears and tails - because they flop. They have to be done in stages unless you have a tail armature (and ear armatures? What would you use?). I've found you have to do a basic shape (or armature) with the epoxy to build on later when hardened. Sometimes ears have to be done in 3-4 stages because they're so delicate and mostly point straight up (something epoxy doesn't like to do).
Elaine's alternate method:
I do tails in stages. First I just sort of build the basic shape (and I try to build it so it isn't a great big weight just hanging by a tiny narrow bit at the dock, because those seem to break), and then I'll put epoxy all over it and do the sculpting. You can do it all in one go for certain shapes, but I find it easier to do a quick-n-dirty base, and then build the detail on top. I have also used a wire and aluminum foil armature for the tail, which works pretty well to keep the whole thing light when I want a nice bushy effect.
When I am doing the actual 'hairs,' I place the epoxy down and then let it set for a bit before working it. One thing that works really well is to put the epoxy down in 'snake' sections, so that the mane (or tail) already has a bit of texture to it, rather than doing it in a sheet of epoxy. Depending on the effect you want, you can just blend the 'snakes' together a bit, or you can (after giving the epoxy maybe 15- 30 minutes to set up) go back over with a pencil moistened with alcohol and draw in individual hairs, sometimes blending the snakes together and sometimes letting them stay very distinct. It's fun!
This Clydesdale gelding was created from the Little Bit drafter, and features a new sculpted mane and tail, sculpted feathers, and brand new ears, eyes, and muzzle.
Don't be afraid to wrinkle and 'smush' the epoxy a bit. On tail tips especially, you'll need to support the off side with a moistened fingertip while you stroke the other side with the pencil. Unfortunately, this tends to crush what you already did! Don't worry; you just keep going back and forth until the epoxy is stiff enough to hold exactly the look you wanted. When you like it, it's done!
With ears, I start with epoxy that's stiffened just a bit, and then shape them into ear shapes and leave them on some wax paper for about a half hour. I make the ear shape by flattening the epoxy into a 'leaf' (oval with a pointy end), then curl it to make the shape of the ear and curve the tip inward a bit. I usually have to go back to make the final profile of the ear correct along the back where it attaches to the head; on the first pass, I only concern myself with the shaping of the front. Sometimes I put them directly on the horse, and just check it every 10 minutes or so to prop up the tips if they're sagging. I've also had good success with shaping the ears, letting them cure on the wax paper, and then attaching them later with fresh (stiffened, again) epoxy. But I always do the entire ear in a single "go." Often, I find that making fresh ears is easier (and more elegant) than carving out the original plastic ones. This is especially true if I want to turn the ears at all.
Cash For Gold was created from the SM QH stallion. Sculpted manes and tails are easier on minis, since they aren't so heavy that you have to worry about support, and can be very effective.
On larger horses, especially horses with a large tail, an armature can be important. I have one piece (in progress) where a #8 threaded stainless steel rod was used as the armature, because the horse's third point of support is from the tail. If you build a tail that is thin at the dock, it will very likely break in shipment without some additional interior support.