Found it, I've used this light, has the correct filter installed.
Makes all ground types look black, even white clays.
The only thing you will see with this is opal.
365nm is that right wavelength I can't remember the name/number of the correct filter needed that goes over it that blocks out what you don't want to see and illuminate what you do.
The light will charge the tiny amount of uranium present even in common opal(potch) and coloured opal(the stuff...
This was found covered in pipe clay in one of the drives a couple of weeks ago.
Was told it's an old Chinese soy sauce bottle?
It's another reason why I haven't bothered sampling..
Custom carbon fibre shaft extended as long as the coil lead will go for maximum reach, I hear ya with the lateral problem. Skid the coil, no weight ,2 arms swinging, all problems solved 😎