You would use a release agent- for urethanes a silicone release should work well.
Or a wax that is NOT water based.
The issue in my mind is that no matter WHAT clear material you make the wings out of, short of glass, they will yellow over time. So anytime I have to make something for display that involves clear parts- I generally plan to make it out of the most stable clear resin I can that is not too fragile… and water clear urethanes fit that bill nicely- they will last longer, are resistant to breakage and can be painted and clear coated with a UV resistant urethane top coat.
There are 2 ways to make the mold- one would be to print the tool you would cast into…that would end up being a rigid tool into which you would be casting a rigid resin. That is simply creating 2 keyed blocks each of which has a cavity printing one half of the wing shape.
The Other way is to print a Split master. That is 2 keyed blocks also- but instead of a cavity- each block has a Positive image of half the wing. With this tool you would take the print and pour a thin silicone rubber over each half- the 2 silicone parts would then be peeled off the split master halves, and fit together with keyed surfaces, to form the final mold- but your mold would be in a flexible rubber capable of casting multiple copies and easily releasing from your cast parts.
the silicone mold would require No release agent- cast silicone releases cleanly from acrylics like grey resin- and no release would be needed for the urethane- so your parts would be both dry and clean of any release and easier to paint with better paint bonding.
The only issue here is to find out if the water clear urethane you can source has an inhibition issue with certain silicones- condensation cure silicone’s give off ethanol vapor that can prevent certain water clear urethanes from compounding properly. So find out what silicone they are compatible with before pouring silicone mold parts.
PS- Durable printed that thin is still not clear- and its really bendy.