I've been looking into this myself so here are some links for metals.
I plan to buy some of this material note they are an actual manufacturer:
www.ebay.com/ Search item # 200428350147
Here is their home page:
www.hallmarkmetals.net/index.htm
Good people, and they directed me to this site and its forums.
Check out his "See other items." Link. This is an excellent price for 6 pounds of white metal with silver. They also sell a 92-8 that is highly regarded for fine detail but here you are in pewter territory so electroplating would likely be necessary for finished jewelry. His MPK sounds perfect for my needs.
I am guessing here and relating what I learned when I called Contenti. And based on experiments with other similar metals I have collected. You will need to do your own trials or experiments or whatever you refer to it as.
MPK should result in a silver finish with polishing or "tubing" that is professional cleaners and ceramic media in a vibratory machine.
Here are a couple jewelers suppliers that will have most everything you need, but as always it pays to comparison shop, especially for raw materials.
www.contenti.com/index.html
Got to a knowledgable person quickly today and have bought tools from them including fine finishing burs that are most excellent.
www.riogrande.com/
Good folks but not as helpful knowledge wise, and often send slightly wrong stuff but quick to discount you in that case and have the best prices on much of their stuff.
Here is where you can get new Lee 10 pound pot the cheapest.
www.Cabelas.com I see the link is ridiculously long so if it doesn't work just search Lee Pot.
www.cabelas.com/cabelas/en/templates/links/link.jsp;jsessionid=AVRLTBPV310RTLAQBBICCNVMCAEFCIWE?id=0002838210653a&type=product&cmCat=SEARCH_all&returnPage=search-results1.jsp&Ntt=lee+pot&Ntk=Product_liberal&sort=all&Go.y=0&_D%3AhasJS=+&N=0&_D%3Asort=+&Nty=1&hasJS=true&_DARGS=%2Fcabelas%2Fen%2Fcommon%2Fsearch%2Fsearch-box.jsp.form1&Go.x=0&_dyncharset=ISO-8859-1&_requestid=108732
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.
This is my first post in these forums, I hope you or someone finds something of use in it.
Stephen Casey