[V_TWIN]

You must not have read the whole story:

“Straight away he (the doctor) identified it as black henna. I didn’t realise it was different to any other type of henna. ‘He explained it contains chemicals which aren’t meant to be used and told me that it’d burnt her skin.”

[Sans-Culotte]

Nope, did not see the part about black henna. Didn't know there was such a thing. I actually use henna to dye my facial hair, which is grayer than the hair on my head. It's a green powder that I mix with water into a paste. I use it because it is quite mild in comparison with other dyes.

The people who sell the henna that I use offer it in different colors for differing shades of hair (some people dye the hair on their head with it). I use one that results in dark brown. They also have henna for black hair. Maybe it is the "black henna"?