Advice: Never use BLACK HENNA
Never use BLACK HENNA. Don't even go near it. A chemical called PPD, present in black henna, can cause chemical burns on your skin. Escaping an allergic reaction the first time you use black henna does not mean that you will have the same luck next time. Some artist/henna supplier listings here may use black henna. I have attempted to contact artists to learn whether they use black henna, and I appreciate your feedback on artists. However, ultimately it is up to you to find out whether artists use black henna or not. This task is not easy, but interviewing your artist carefully will help.
Henna is NOT black.
Henna does NOT cause blisters and open sores.
PPD black hair dye CAN cause blisters and sores.
This dolphin was done with PPD black hair dye,
but the artist called it "Black Henna".
There are several things marketed as "Black Henna", and some things believed to be "Black Henna". Some are very dangerous. Some are harmless.
When para-phenylenediamine is used to make black temporary tattoos, often called “black henna”, it can cause blistering, open sores, scarring, and lifelong health problems.