Please pardon the click bait on this link (not the most reliable source, I know), but although there is a lot written about this tragic story, I like the pace of this piece:
Given the 1,000+ year half-life of radium (and that the victims' bodies may still be glowing), I wonder if there is a simple effect here using cabinet cards, and the curse of The Radium Girls...
A story is told of one of these women, perhaps Margaret Looney - one of the first to pass - who was so distraught by her condition she was rumored to have held her portrait close to her, refusing to let it go until the day she died. It apparently reminded her of who she was, not what she had become.
The routine ultimately settles on the spectator choosing the portrait of one woman he thinks may be a Radium Girl. Perhaps Ms. Looney is trying to tell people the story of The Radium Girls, even after her demise. The room lights are turned off, and a special lamp is passed over the cards that were not selected. They all appear perfectly normal. Then, the light is passed over the spectator's chosen portrait, and the audience gasps. The portrait is covered with glowing fingerprints...