This article is from the Tattoo FAQ, by Stan Schwarz with numerous contributions by others.
Fluorescent ink is not the same as glow-in-the-dark ink. Fluorescent
inks glow under ultraviolet light. Phosphorescents glow after being
exposed to light, and glow-in-the-dark things that glow without any
outside stimulus are almost unknown.
There are *no* glow-in-the dark inks.
There are *no* phosphorescent inks.
For a brief time around 1991, some tattoo artists experimented with
fluorescent inks that glow under UV light. At the time, it was
thought that these could be used to make tattoos that would only be
visible under UV light. As it turned out, these inks did not perform
as expected. They were not invisible under normal light, and in some
cases turned brown. At the same time, many people reported skin
irritation problems. As a result, we are not currently aware of any
tattoo artists still using these inks.
There is a collection of information about these inks at:
http://www.bme.freeq.com/spc/experiences/glow/
 
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