It's an old way of preparing amadou by using salt peter (potassium nitrate) and it can be made using rotten vegetable matter, urine and wood ashes, but it's much easier and more convenient to use ready made KNO3
First find your source of Amadou, horses hoof fungus is in short supply in my part of the world so I use Artists Conk, it's every bit as good as any other fungus.
get it off the tree , take off the pores and outer layer just to leave the trama (amadou) layer
once cut off you will need to dry it properly until it is totally dry, this is imperative
to make your salt peter solution you will need 30g of salt peter to 1 litre of boiling water.. this is my recipe and I find it perfect but you may want to alter this to suit your own needs
pour your boiling water into a stainless or glass container and add the 30g of salt peter.. you DO NOT NEED TO BOIL THE AMADOU!!!
I often hear people say you need to boil the amadou for hours and hours, it's not necessary at all.
Add in your dry amadou and allow it to soak up the solution, this only takes a few hours but you can leave it over night to be sure..
once it's very nearly dry, pound it with a stick to break up the fibers in the amadou and tease them out a little bit
once you've done that you can see they look like dark rabbit fur, it's really gorgeous looking!
last think to do is test it.. a flake of jasper and a steel and this piece took on the first strike and burned beautifully!
As a point of interest it's often Said that Prometheus brought fire from the Gods, but study of the ancient Greek texts actually say that he brought the method of catching the sparks from which he could create fire.. so maybe Prometheus himself actually used amadou to bring us the element of Fire!!