There was something I considered was impedance its a dynamic measurement. and I can hit it with AC setting on my TIG welder that I use for welding aluminium.
The crystal that I have been working with has no faults. but I have one that does its 4 in dia

I have a black light around here somewhere
It just hit me, I am a ASE L1 Master tech. We use UV dye to check for refrigerant leaks. I actually have a UV lamp its 12volt and is bright as hell and can only be on intermittently because it overheats.
It does not florescence (the crystal)