Aquadoodle

Aquadoodle is an activity drawing toy primarily for preschool aged children. The patented invention is based on a hydrochromatic ink which causes color change when the user draws with a water filled pen. The user`s drawings will remain for several minutes before gradually disappearing. The hydrochromic ink technology was created by the Pilot Ink ....
Found on http://en.wikipedia.org/wiki/Aquadoodle
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