So we had quite the mystery when artist Natalee Morse emailed us to ask why her Tall Tower puzzle had "darkened" since she bought it a few years ago.
I have to admit, at first I thought she was just mis-remembering how the colors, or doing the puzzle under different lighting conditions, as in general printed colors tend to lighten and fade over time, not darken!
But as an artist she knows her colors and was steadfast that her other puzzles hadn't changed but that this one had.
We were quite puzzled as to how a puzzle could darken!
Then she realized her daughter had stored the puzzle in plastic bags!
We are pretty sure that was the culprit somehow, though we are not positive why storing it in a plastic bag could darken the print.
My hypothesis is the bag somehow got humid (we've all seen plastic bags fog up), and the puzzle got damp, and we know spilling water on a puzzle will darken it.
However, Natalee thinks it might be something about the plastic itself, based on her past experience:
Indeed, as a retired preservation librarian I can tell you that yes, ordinary plastic (PVC) bags release destructive gases. For archival purposes (like keeping wooden jigsaw puzzles), you want inert plastics: mylar, polypropylene, or polyethylene. Not eco-friendly, but if they degraded, they wouldn’t be archival.
Here is more info: