Black stain spreading on keris during vinegar cleaning

[A. G. Maisey]

Actually Jean, sulphur and salt has an erosive effect.

I once saw a keris blade taken from a bath of sulphur and salt, it had been in the bath for about a week and had been forgotten. More than 50% of the blade had been eaten.

Why?

The sulphur and salt was mixed with water so it was a slurry, but these two things are opposites.

I do not understand.