Black stain spreading on keris during vinegar cleaning

[Jean]

Originally Posted by jagabuwana

Jean, what do you think the role of rice water (effectively starch) is in this method?

I don't know Jaga, probably no chemical effect but getting a more homogeneous slurry? The black colour of the blade seems to indicate the presence of iron sulphide.
And I would say that sulphur and salt have an corrosive effect (chemical wear) rather than erosive (mechanical wear)?
Regards