I have been preserving autumn leaves today, for use at a craft workshop I am running in a few weeks time.
The method is quite simple, pick leaves, immerse in a mixture of 1 part glycerine, 2 parts water mix in a tray. Make sure the leaves are submerged, you might want to put something on top of them. Keep away from children and pets!
I will let you know how it turned out in a few days time.