Hi Pam,
Yes, it definitely helps - it sounds like an Ambrotype to me. This is an image on glass and you are quite right, the image is reversed because in reality the Ambrotype is a "direct positive", i.e. the glass was put in the camera, the photo taken, and then the glass had a negative image on it. The glass was taken out of the camera and processed, and then assembled, usually in this order: black card, black painted back of the glass, or black cloth; photograph; metal frame (usually oval or some fancy shape); a piece of cover glass; paper tape to seal around all the edges; a gold coloured metal frame around teh whole lot; put the package into the tray or box and there you are!
They're beautiful things and you are lucky to have one. If you can manage to post a picture of it, I'd love to see it and just confirm that it is what I say it is!!
If no-one else comes up with the info, I'll see if I can find out how much people would have had to pay for one of these photos. Are you in the UK?
Cheers
Prue