Ah ye gods and little fishes, the boiling urine again
Okay, I think several ideas have become conflated to turn out this one.
Cut up and boiled fomes fomentaria is a good dyestuff. If the amadou layer is then dried a little and then pounded it makes a good spark catch. If it's soaked in saltpetre it's even better.
The muddle comes when *stale* urine, that is ammonia, is used to clean wool before it is dyed (it's an excellent degreaser and removes the lanolin leaving the wool receptive to a dye). Ammonia is also used to *pull* a reluctant dye from lichens & fungi.
Piddling into a straw pit was an old way of obtaining saltpetre for gunpowder.
Somehow or other all these ideas become mixed up and we have the truly appalling scenario of some poor sod boiling up his amadou in urine for three days
On the other hand, we really need to trial all these I suppose
Cheers,
Toddy