Archivists do this because framers often used cardboard and scrap wood to back photographs. In some cases, we have seen photographs where the acid in the wood backing has reproduced the knotholes and texture of the wood perfectly right on the photographic print … and ruined the photograph in the process.
Does this mean you shouldn’t have framed family photographs? Of course not. But do disassemble vintage photographs from their frames to check on the backing being used. You can still the vintage picture frames. Just have your local framer replace the backing with acid-free materials (aka museum mounting).
And it doesn’t matter what the frame is made of – the backing should be checked in all instances. You can keep your wooden frames in use if you have the framer redo an acid-free backing.
Another advantage to checking behind those framed photographs is that there may be other treasures tucked away. While visiting my mother last spring, I was taking a small photograph of my grandmother and father out of its frame when two carte-de-visites taken in Sweden tumbled out. Isn’t that great?
Let me know what you find behind those family photographs.