Assuming the jewellers position? On the floor looking for lost stones a laser pointer can be positioned for the beam to just touch the floor surface and the area can be swept like radar the stone shows up quite dramatically even 2 pointers. A black light/UV can also be used to find diamonds, sometimes, yup you turn the lights off and find them in the dark.
Black light/UV that is an ingenious idea! So simple and obvious.
I love it. I keep one of those long soft brushes used by
architects to sweep away eraser dust hanging from a nail on the
side of my bench to quickly sweep an area so I can find my flying
objects and pray to the Floor Gods to help me out.