Here are number of web sites for more than you will ever need to
know about casting and mould making RTV Smooth on has great videos
and are worth the cost.
Is an industrial supply for the casting industry they have good info
on their site.
Video's of making of a mould and casting resin
Micromark has small kits for casting along with the low temp metal
to use in the RTV or to make a metal model.
The usual disclaimer apply satisfied customer
glen, been there done that, and got it all over the shop!