Each fall, I wander through my yard, down my street, or in parks looking for interesting fallen leaves. I don't want to pull leaves directly off the plant, so I focused on the ground for gathering. After pressing the plants or leaves into the clay, most of the time they couldn't be reused because they would tear when I lifted them from the clay, or they would only be good for a day until they dried out and crumbled when pressed.
This past fall, I employed a method of preservation that has allowed me to use the leaves I gathered months ago, and except for some tips breaking off, I have been able to reuse them as much as I want!
I left them for about 24-48 hours, and looked at the leaves from time to time. They change color a bit, looking darker and you can see where the glycerin has absorbed into the leaf and replaced the water. I removed them, patted them off with paper towels, and left them to fully dry.