Phthalo Blue PB15:3 is a structural variant of Phthalo Blue PB15 that produces more greenish tones.
Phthalo Blues are completely lightfast and stable and are permanent for all paint uses. They are currently used in inks, coatings, and many plastics due to their stability and are considered a standard pigment in printing ink and the packaging industry.
Phthalo Blues have no significant hazards, although those made before 1982 contained some PCBs (polychlorinated biphenyls).
Developed by chemists using the trade name Monastral Blue, the organic blue dyestuff now known as Phthalo Blue was presented as a pigment in November 1935 in London. Its discovery was accidental. The dark color was observed in a kettle where a dye was being made from a British dyestuff plant. The demand for such a pigment came from commercial printers who wanted a cyan to replace Prussian Blue.