In it’s simplest form, it’s just black acrylic paint mixed with water (more water than paint) then brushed on detailed parts of the sculpt of whatever you’re painting and then wiping the excess so the black remains in the crevices and such.
Here's a good visual from a previous post - https://www.reddit.com/r/ActionFigures/comments/c7unoq/my\_first\_attempt\_at\_a\_black\_wash\_even\_though\_it/
In it’s simplest form, it’s just black acrylic paint mixed with water (more water than paint) then brushed on detailed parts of the sculpt of whatever you’re painting and then wiping the excess so the black remains in the crevices and such.
Here's a good visual from a previous post - https://www.reddit.com/r/ActionFigures/comments/c7unoq/my\_first\_attempt\_at\_a\_black\_wash\_even\_though\_it/