The lichen i use i gather up along the side of the road or in the woods. Then i make a mix of glycerin and a dye of whatever color i want and boil it outside for about 4 or 5 mins. Then take it out and squeeze out the excess dye and glycerin and let dry. I have several bags in my basement that are at least 5 yrs old and is still soft and pliable.
I have taken and boiled old hard lichen and it has worked on that too.