Lawsone explained
Chemically, lawsone is 2-hydroxy-1,4-naphthoquinone. It is released from the leaf powder when it is mixed with a mildly acidic liquid and left to rest - a process artists call dye release.
The amount of lawsone in a batch of powder largely determines how dark the final stain can be. Good body-art powders are tested for lawsone content and freshness.
Also searched as: hennotannic acid · henna dye molecule · lawsone dye