Pour two parts glycerin and one part water into a plastic bin. Add fresh fall leaves in a single layer, making sure that they are fully submerged in the solution. Let them soak for three to five days, then take them out and dry them off. By replacing the natural moisture in the leaves with glycerin, the leaves last longer. The color will stay, although it may change slightly, and the leaves should remain pliable, instead of getting dry and brittle.