I have tried both UV lights, and Ruby filters + a microscope to try to detect Lead glass filling. It seeems that lead filled gems are much less active under UV.
The red Ruby filter inline with a microscope seems to show dead areas where (presumably) the leaded glass is affixed. Are either of these methods a viable way to sort Rubies to detect lead glass filling?
Mainly, you want to look under magnification and look for the blue flash. Also, there can be bubbles in the filled fractures. Just remember, flux healed rubies can also have bubbles in the healed fracture.
Uv, ruby filter or Chelsea filter are not diagnostic, because some rubies may have more iron and not show as bright while others may have no iron content. Filters are good for sorting parcels at a show, but use your other tools to make a final determination.
Lead filled and flame fusion ruby are detectable with a loupe or a microscope.
cut lead glass filled ruby under a loop and white light will give off a blue flash I believe. Move the stone around at all angles and where if has filled a crack or whole it will flash blue. Natural Ruby wont give off any kind of blue flash. Takes a keen eye to spot but once you see it you will know for sure.