: Nick, I tried to put some maple leaves that were turning colours last fall
: into my fiberglass but when she dried the leaves had turned brown?
: Reason?
: Answer?

UV, humidity and oxygen all both going to conspire to change the color of anything you put under the glass. As a result you are going to want any thing you use to be dry. Then make sure it is very well sealed. This probably means you want to seal it from the wood as well. Then make sure it is protected by a good UV varnish and also keep it out of the sun as much as possible.

Even done perfectly you will have to expect some discoloration. My brother put some green fern fronds under the glass on the inside and outside of the hatch of one of his early boats. Those on the outside turned brown rather quickly, those on the inside stayed green for years. I don't know if he still has that boat or the current condition of the ferns.

I would place leaves under a carpet for a few months to get them flat and dry and to see how the color holds up.