I have a number of original photos from the late 1800's through the 1930's that were mounted on non-archival cardboard. It was probably done in the 1960's and it looks to me like they were dry mounted. The photos themselves are in fairly good condition. How can I get them off? Can I heat them with a dry-mounting iron? I really need to remove them because a flood damaged other areas of the cardboard. (The water damage and mold has not touched the photos)
thanks....

You could try a hand-held hair dryer set to hot. Then use a very thin spatula, (the one I have is only 3/4" wide), and gently start to lift the print from the cardboard. I have used this method to remove prints from those old "magnetic" album pages. It may not work with old dry mount tissue the hair dryer may not be hot enough to soften the tissue. If you try this, let us know

It worked! I used a palette knife and a 1875 watt hair dryer. It was slow going and worked best when I left the dry mount tissue attached to the photo but removed it from the board. Thank you so much.