Well, fiberglass is like using paper mache, the fiberglass mat is like the newspaper strips... in our case a mixture of 30gm (tissue), 300gm and 450gm, the various thicknesses of the mats. The resin (general purpose resin) is the flour and water.
For small detail sections we will mould and cast these in Polyurethane Resin, we might cast the hand plate in this.. undecided yet. This resin is normally a white/ivory colour and what most small solid props are made from.
As for silicone. We use T28 Silicone Rubber + T6 Catalyst, normally purchased from Tiranti. They provide very good silicone, great consistency to work with (add a bit of thixo in) and produces really strong moulds.
Onto the clay, we use Chavant NSP Medium Sulphur Free non drying modeling clay. Great stuff!
Hope that helps.
Jon