Pamor Staining in the UK?

[Pusaka]

Harmful substances are heavily regulated in the UK, you might be able to find someone who will sell you some but it would be probably easer to import it.
I wonder what other substances could be used to etch keris, I think I recall reading that before the use of arsenic a concentrated citric acid from limes etc was heated and the keris blade was placed into the hot liquid to etch.