Henk, that was an etch with sulphuric acid, not a stain with sulphur.
You can get some sort of a result with just about any acid, nitric is probably the best result from an acid, but its horrible stuff to use, and I would not recommend it.
The sulphur stain job that I did years and years ago was powder sulphur mixed to a paste. The description in the book called for it to be wrapped in a banana leaf, but I wrapped it in plastic.The process took about a week.
I've had a look for that book, but its not in my book cases, which means it is in a cardboard box in my garage. I forget the name, but it was by an Englishman, it was an Oxford University Press reprint, and it has red dust covers.I'll locate it one day.
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