Fluorescene (green) and rhodamine (red) are common water soluable
fluorescent dyes that are fairly safe (i.e., not carcinogenic).  They
should be available from most chemical suppliers. These are the dyes
added to the antifreeze you put in your car's radiator.

--
Winston Chan                            | phone: (319) 353-2398
Dept. of Electrical Engineering         | fax: (319) 353-1115
University of Iowa                      | email: wkchan@icaen.uiowa.edu
Iowa City, IA 52242