I bought this past weekend the first RTV I have ever had.
For those of you who don't already know, RTV stands for Room Temperature Vulcanizing. It's a silicone rubber material used to make molds for casting resin, plaster, etc. It generally can NOT be used for lead - the temperature is too high, melting the mold. I believe there are some types that can handle the high heat, though.
What I got was a Smooth-On product, called OOMO 30, IIRC. It mixes in equal parts by volume (easy!). I have read good things about it on the internet, at TMP and other places. Found it at a local art supply store.
So, obviously, the plan is to sculpt up some items, make molds, and get to casting. Some of these things will be scenics related, so I thought I would mention it here. Specifically, I want to create some doors and windows to be attached to buildings, in both 15mm and 25mm scales. It is a pain to try and scratch build them each time, so I am going to try and create some good masters to cast from. Might make some railings, chimneys and such, too. Start simple before trying something ambitious.
Anyway, wish me luck. I have a nasty feeling I am gonna need it. When I get a space cleared to work on it, I'll get to work. Hopefully, pictures and such will be involved as well.