I've only ever used it as a stain for Walnut. Works great for that and your fingers.
It does go on the wood purple,,but then turns a nice med to deep brown color. No heat needed as in AF treatment.
Heavy purple colored crystals are usually in the hardware section of HomeDepot and Sears type stores.
They are used in water systems to regenerate iron removal filters. Comes in plastic jars now.
A small 6oz jar will last a long time.
A table spoon of the crystals in a cup of water is about the mix I have always used. Nothing fancy about it.
Remember that it is a water-based stain and will raise the grain.
Once mixed,,it lasts forever it seems. I've got a small jar mixed up under the bench that's been there for the last 8 or 10 years probably and still works fine.
I like it for touch up work in restoration especially.
Get it on anything,,clothes, furniture, rugs, etc,,and it's there for eternity.
I've read that it somehow rusts and pits steel that comes into contact with wood stained with it.
I've used it for 30+ years and never saw any such rust. Mostly used it on pistol grips, but some rifle and shotgun stocks too. Many of those I've had occasion to re-examine over the years and have seen no rust.
A furniture maker type did tell me it made his maple stuff look green especially when viewed under florescent lights. But as I said, I've never used it on anything but Walnut.
It'll stain leather nicely too like everything else it touches. A little mixed up in some cool water and soak the leather piece in it and let dry naturally. I don't know if the Permanganate does anything to leather but I know a couple of people that use the stuff.
Just an extra trick in the bag to try when the other jars of stain in the row don't seem to work right or you want something a bit different.