XRF is x-ray fluorescence, a non-destructive method for determining the composition of materials based on illuminating them with x-rays and observing the emitted fluorescence.
They are now handheld:
(Image credit: Niton)
It's basically a tricorder. Point it at a metal and it'll tell you the composition. I'd like to get one to probe watch cases, bands, etc. I strongly suspect I'd learn that 316L varies quite a bit, and that some companies cut corners on steel.
They even look Star Trek:
(Image credit: Bruker)
I've seen used units on ebay, and would likely go that route to get one. Please donate if you'd like to see WatchOtaku gain this capability!