Create an evening-sky image that glows realistically under black light. Use glow-in-the-dark chalk to draw spots for stars and a circular shape for the moon. Draw on a pale or white wall and ceiling so that the sky image will only show up in the dark, just like the real celestial objects in a night sky. While this effect will work in normal darkness, the stars and moon will have a particularly intense glow beneath a black light, as well as the appearance of added dimension.
Hide portions of white black light chalk within a white wall or the white portions of an image to create symbols or a picture that will only show up clearly under the special lighting. Create a hidden image within the colors of the original image, emphasizing areas that would otherwise have been less noticeable. Alternately, trace outline areas of the image in order to transform a more complete, realistic image into a symbolic representation by night; for example, outline the top of a mountain range to create a curvy line representing its shape.
For a humorous chalk art gimmick, use the glowing chalk to give austere, old-fashioned portrait painting props features that glow under black light, especially eyes. You can also add humorous add-ons like speech bubbles or hats.This idea makes a tongue-in-cheek decoration, fitting for haunted Halloween effects.
Mandalas are a sacred Buddhist/Hindu art form consisting of complex geometric images enclosed in circles. Draw a mandala freehand or use a black-and-white coloring sheet. Color the outside of the mandala sheet black and use color inside the shapes of the mandala itself. Under black light, the black area will recede while the colored portion will appear to come forward and glow.
Make face masks from papier mache and paint them black, or paint plastic craft store masks. Decorate the masks with lines of glowing chalk, using the black foundation much like a school chalkboard. These completed masks will have a striking look even in normal light, but in black light, all but the colored lines will seem to disappear. If the wearer dresses in black garb (including a black ski mask), the lines of the mask will seem to float in mid air.