Unique way to home test without damaging .999 silver:
Hard boil an egg. Once finished, while egg is still hot, mush it up and put on a plate. Place silver near egg and wrap up with saran wrap, so mostly air tight. (Could also use Tupperware or anything that keeps air from escaping whatever you are using.) The sulfur gases released from the egg will turn the .999 silver coloring into a beautiful rainbow.

To return back into shiny silver color again. Wash with a little soap in warm water, dip in acetone for 3-5 seconds. Rinse off with water....and .999 silver back to original condition, undamaged.

EDIT: If you have children, it's a fun science experiment to do with them.