Rub the petroleum jelly onto your hands (avoid getting in eyes).
Hold your hands under a black light.
Ta-da, they are glowing!
You can even try writing with the petroleum jelly on a piece of paper to create glowing messages.
How does it work? Black lights were given their name for a reason - they give off very little light that our eyes can actually see. Visible light contains a spectrum of colors from red to violet, but beyond violet light is ultraviolet light. We cannot see UV light. The type of UV light found in black lights are very low energy, not like the ones emitted from the sun, so you cannot get a sunburn from black lights. Petroleum jelly contains substances called phosphors. A phosphor absorbs radiation and emits it as visible light. The phosphors in the jelly are absorbing the invisible ultraviolet radiation from the black light and emitting visible light.