Pewter. That's interesting. I don't know how strong that stuff actually is.
If you're restricted to low-temperature casting, it might be helpful to visit your nearest high-quality metal scrap yard and see if they have any zinc die-casting alloy. These guys know metals rather well and can likely give you hints on melting temperatures and such. Most die-casting today is done with aluminum, but that requires a crucible that can withstand a fairly violent furnace.
Having said that, I can attest that it's fun to melt aluminum: dig a 12" hole in the ground, bury a pipe so that it slants down into the bottom of that hole, fill the hole with charcoal from the grocery store, dump in some crumpled newspaper and maybe charcoal lighter, add a match, wait a few minutes for the charcoal to catch, and then apply an old hair dryer to the pipe (you can attach it to the pipe with duct tape for an added touch of elegance.)
When the air from the hair dryer (set it on 'cold') reaches the smoldering charcoal interesting things start to happen: red flames issue from the ground, and the roar of the fire will keep the neighbors from ever bothering you again. Smoke issues from cracks in the soil near the hole.
Do not use the family barbecue grill for this sort of thing, for it will essentially burn up.
The crucible can be a piece of iron pipe closed at one end: feed it crushed aluminum cans and other aluminum scrap. Molten aluminum doesn't glow brightly, so caution is advised. Borrow a tablet of swimming-pool chlorine and dump it into the melt to purge dissolved gases and thus eliminate bubbles, and pour your casting.
You will never look at an aluminum shower stall or screen door the same way again.
M Kinsler