Nice, the sun test will tell you alot. If it greys or goes purple, that definately points to silver chloride, and vinegar won’t move it, so a quick hot-water dip is a cross-check for lead chloride. If it does darken, you can reduce a small pinch with aluminum foil plus baking soda in warm water to prove it’s silver, then keep the bulk for a cleaner run later. Mind keeping one speck sealed in the dark as control so your sure the change is light-driven? :)