The K-55 is filled with fluorescent, water-based inks that are environmentally friendly and odor free, perfect for use indoors where solvent fumes are undesirable. True to their name these fluorescent colors will glow under a black light. The K-55 is available in 5 colors. 30ml Ink is water-based and does not contain harmful solvents. Xylene free. Conforms to ASTM D-4236. Handmade in the USA.