Gather leaves that are freshly turned and still flexible, or branches cut the same day. Discard anything spotted, torn, or already dry.
Wipe each leaf clean and blot it dry with a paper towel.
Mix 1/2 cup glycerin with 1 cup warm water and stir until the glycerin dissolves completely.
Arrange the leaves in a shallow dish in loose layers so the liquid can reach every surface.
Pour the solution over the leaves until they are fully submerged, then nest a second dish or a few clay pots on top to keep them under the surface.
Place the dish out of direct sunlight and leave it for 3 to 6 days, checking on day 3. Leaves are done when they bend easily without creasing.
Remove the leaves, lay them on paper towels, and pat away any excess solution. Let them rest overnight before using.
For branches, cut stems about 18 inches long, strip the lower 6 inches of leaves, and crush or split the cut end with a hammer or pruners.
Mix 1 part glycerin with 3 parts hot water and pour about 3 inches into a heavy jar.
Stand the branches in the jar, keep it in a warm spot out of the sun, and top up the solution as it drops. Allow 2 to 6 weeks; thick leaves like magnolia take the longest.
When the leaves feel smooth and have changed color to the tips, remove the branches, wipe the stems, and let them air out in an empty vase for a few days before arranging.