Lightfastness is reported by third party sources to be poor-- quite fugitive. This pigment may actually descend to a blue wool scale of 1 on a scale of 8, with 8 being good and 1 being basically falling off the bottom of the scale.
In addition to poor lightfastness this may metabolize to a known carcinogen, see Monona Rossol's work to learn more. She notes that it may also be contaminated with PCBs.
We were very surprised to find this pigment in artists oils. One manufacturer, who is quite well thought of, mentioned its stability and reports the lightfastness of their version as ASTM II, so perhaps there is some variety.
We wondered if there is some discrepancy somewhere, as artiscreation reports quite sorrowful lightfastness testing for PY14 with the low end of moderate for masstone and dramatic fading in tints. We wondered if there was a typo somewhere, and we checked the six digit code reported by the manufacturer (21095). It does indeed seem to be PY14 and both sources mention that the color is used mainly in printing. Perhaps doing one's own lightfastness tests would be useful.
PY14 comes in several different varieties which differ in opacity.
