I have a small pile of tin ingots from a cleanout of my dad's former casting area. They're labeled "Tin", and look and sound different than lead ingots, so I have no doubt they are tin. They do have a "Lyman" mark from an ingot mold so I doubt it's from a commercial supplier like Roto. Whoever did cast them made them thinner than the lead ingots typically are, which was smart, so you can tell at a glance it's the tin.
I have a the question out to my dad on if he recalls the source, but in the meantime is there a cost efficient way to test them? I'll be selling them so I'd like to have some idea of the pureness or at least the source. Thanks!
UPDATE EDIT: I'll leave the above original text for context. I talked to him on the phone last night and he's said he had it for about 30 years. He used to do a lot of lead wheel weight melting and he'd alloy with these. He'd keep them handy by the casting machine for when he did full wadcutters too, as sometimes he'd need to add a little extra tin if he was having trouble getting all the grooves to fill in the mold.
He confirmed my assumption that it was melt down and cast into the Lyman ingots by a guy he'd buy tin and lead from occasionally. Most likely source was tin solder, but it's been thirty years and he can't remember. Makes sense to me, though.
Once he switched over to buying ingots from suppliers rather than melting the wheel weights (the smoke from the ever present rubber stems, stickers, and trash in the buckets... ugh... ) he didn't really use much of it anymore and it sat on the shelf.
FINAL EDIT: Great suggestion to contact user BNE on here. I did exactly that, followed his instructions to send him a sample, and received the following result:
Sn = 99.6%
Cu = 0.4%
Excellent! Granted it's not a certification by any means but definitely gives me a good idea of what I actually have.