Some notes I copy pasted out of the stopmotion forums on working with silicone (for the corpse bride/ coraline smoothness)
Silicone is not a foam, so it is heavier.
You need a sulphur-free plasticine to sculpt with.
You can only paint it with more silicone, and it needs thinning to make it handle a little like paint. But too much thinner, or too much pigment, can inhibit the cure.
Like latex, it has a limited shelf life
But on the plus side, it doesn't wrinkle like foam latex so it's better for characters that need smooth skin.
And it should last for many years, unlike latex which deteriorates. The puppet will suffer wear from animating it, but it could probably sit in a display case forever.
It has a slight translucent quality which can look very lifelike.
Silicone is infamous for not sticking to armature/wire, which means it can sometimes slip or rotate. a suggestion is to wrap string/cotton around the armature so the silicone has something to grip onto or soak into.
The 'official' paint for Silicone is 'Psycho Paint', which is another silicone that has a much longer setting time. But people have had luck tinting it with acrylic and oil paint.
I use dragon skin pro and I am really satisfied with how it performs. I tint it with oil paints and then if I need to paint it with thinned silicone (I use naphtha) tinted with oil and dried with a hair dryer.
Smooth-On's Dragon Skin and PolyTek's Platsil Gel-10 are popular platinum silicones with a shore hardness of 10A.
A broad outline of the process:
First sculpt the character in a sulphur-free plasticine (like Chavant NSP_, or an unbaked polymer clay (Sculpey, Fimo, etc) if you prefer that stuff.
Second, make a mould from a hard plaster (like Ultracal 30 or Hydrostone) - usually in 2 halves, a front and a back piece.
Third, open the mould and remove the plasticine, make the armature to fit in the mould.
Fourth, cast in silicone rubber with the armature inside.
Fifth, remove silicone puppet, trim flashing, fill any gaps, clean up, and paint with more silicone and pigment.