I purchased an estate in 2015. I do not know the composition of the caster's alloy (if any) - which are an alloy and which are "pure" (mostly) lead.
I do "note-by-inspection" (and not the lighting) that those I believe to be "pure" lead are dull silver and exhibit white lead-carbonate "corrosion". Those presumed to be an alloy of lead with an unknown percentage of tin (2%? to 5%?) exhibit as "shiny" silver with no lead "corrosion", which are nice properties.
These current comparison are for boolits that were cast and "canned" more than 6-years ago. I am thinking I will melt the poorer quality (wrinkled and corroded) lead, as well as the boolits of lead-tin alloy in the calibers that I do not shoot, some of which are wrinkled too.