For more context: DIY Matchprint cards
And the most important post from there, probably
Bonus points to the undisclosed CGC employee for actually posting this in that thread
XRF machines are used by some local Pawn or Jewelry shops to differentiate chemical compounds in metals. This machine can be used for anything, and if I recall hearing CGC Cards is using this type of technology to help determine authenticity of collectibles that come through their door.