I think the only way is by using a UV/blacklight, im not 100% sure on that though.
You can pick the little tourches up for a couple of pound off of ebay well worth the investment if your gonna be collecting/dealing with glass. Ive also got a large strip light on for home but i think i paid about £20 for that so still not incredibly expensive
If there is Uranium in the glass it will glow bright green (even visable in daylight), manganese glows orange (and i think dull green?), high lead content glows a blue and sometimes white (all under UV)
michelle