utside of x-raying/spectral density determination (pretty sure you don't own or have access to a machine like that) then destructive testing is what is commonly available; however, potassium dichromate test is about the least destructive test out there and should not compromise the amount of junk silver you plan on testing (yeah it will add up over lots of testing but on a %-loss-per-ounce effect it is really small) - pennies per ounce if you get the technique down quick.

Unless you are absolutely postivie about the source, then you need to test it; testing it affordably means NDT is out of the question.

With bars and rounds, it's easy, I just get a powerful magnet and if the bullion is attracted to the bullion, it's a fake since silver is not attracted to magnets. How about junk silver? Modern coins such as nickels, dimes, quarters, halves, and dollars are also non magnetic. If I do the acid test, wouldn't that destroy some of the silver? How do I test junk silver (90%, 40%, and 35%)