How can I safely display a hand-tinted photograph?
Q. Dear Donia,
A. Dear Rita,
What a great idea to be able to enjoy your hand-tinted positive!
As you know, you want to be sure that anything you use for your viewing box to be chemically stable to not cause the image layer of your glass plate to deteriorate. Ideally, the frame would be metal rather than wood but I can understand that this can be expensive. If you are using wood, you will want to seal it to prevent the volatile organic compounds (VOCs) from the wood having an impact on the image. The best way to do this is to seal the wood with a product called Marvelseal. It is a true vapor barrier and will prevent the transmission of VOCs. You can seal only the inside if you want to leave the exterior wood for aesthetic reasons. If you use the Marvelseal you would also want to consider using Volara foam as a gasket to provide extra protection against airborne pollutants.
Not as effective, but easier to use is water- (not oil-) based polyurethane. This will block a good percentage of the VOCs but not all of them. If you use poly, be sure to read the can and let the surface cure completely before putting the frame together and put the glass plate inside.
Good luck with your project and if you have any further questions, please don't hesitate to ask.