Here is a copy of a post I made else wheres. Rebound 25 captures detail down the smallest measure I could see. But most of my experience with it is in molding sculpting waxes and replicating my own resin castings. Not designed for metal casting but I did pull off a few good castings by coating it first with powdered graphite.
www.contenti.com sells fine graphite as well as mica and perfume free talcs.
I have used Smooth-On Silicon for plastic casting for some time and you would learn a good bit browsing their site as well as one of their distributors. Bear in mind successful thick mold in rubber or resin castings for that matter usually require pressure or vacum casting, but not neccasarily, this is a skill set in of its self. Mold-Max 60 is listed as able to handle low melt alloys. I did a few castings in some Rebound 25 and they degraded quickly until I brushed some graphite onto the mold first, and then no wear at all that I could see. That is a durometer-hardness of 25A, So MoldMax 60 although tin based and not platinum would likely do even better.
www.smooth-on.com/
www.reynoldsam.com/
www.reynoldsam.com/index.php?cPath=1135 Haven't tried this rubber yet but I plan to.
