Posted By:
Scott ForrestJohn, I thought this was an item that had been discussed before, but can't find anything. I am about to try removing some 1800's lithos that were glued with "horse glue" to construction paper type album paper, and I'll report back here. We know it can be done, because we've seen the results sold on ebay.
My initial procedure will be to remove as much paper as possible without damaging the litho, then soak for a few minutes (on a non-important litho card for practice). I'm hoping that the litho card is stronger than the backing paper, so that I can rub off the backing paper - horse glue is not water-soluble, so I might be screwed, but we'll see.
For photo-quality cards, you can't soak. What has worked for me: I suggest removing as much paper as possible, then bend up the backing paper and dab water at the intersection of the backing and photo back, making sure the photo is resting on a dry cloth and that you absolutely do not touch the front with wet fingers. I can email you "before and after" scans of a photo I removed spots of paper from.