Invisible black light chalk appears white under normal light. This chalk contains chemicals that glow with color under black light. A picture is pre-drawn on a white background to hide the black light chalk. Black light reveals this ‘invisible’, hidden picture.
For Example, this Chalk art picture was drawn by Cindy Palmer Massey at a women’s meeting. The invisible black light picture of Jesus and child in the sky could not be seen until black lights were turned on at the end of presentation.
The following video is a demonstration of black light chalk by Matt Bowman, artist, instructor, and chalk manufacturer at eternityarts.com.
Not all black lights are the same. There are Incandescent, UV LED, Fluorescent Tube and Mercury Vapor UV Black Lights.