Phosphorescent Glow in the Dark
Phosphorescent ink is made up of phosphorescent powder mixed into a clear ink base.
The powder particles take on a "charge" while worn in a light environment and once charged can be worn into pure darkness and will glow until the charge runs out.
As the ink mixture has no real opacity, this ink is used as an overprint over other light coloured inks.
The phosphorescent flakes have a slight green tinge, so when printed over white ink the result is a slightly off white colour. They also work well when printed over yellow, green & most fluorescent colours.