Aureolin Alert: The Defective Paint

This is a serious warning about Aureolin PY40 (Cobalt Yellow) in ALL brands. Despite the ASTM ‘s good recommendation (rated ASTM II), my tests show that the pigment Aureolin PY40 turns BROWN and FADES even in a dry state. I recommend that you do not use this paint any more. The perfect substitute for Aureolin is Winsor Lemon PY175.

The samples [BELOW] shows how closely Winsor Lemon matches the color of Aureolin- before Aureolin turned brown. Both samples were exposed to exactly the same amount of light. 

Aureolin (cobalt yellow) PY40 (Left)

Winsor Lemon PY175 (right)

Winsor Lemon PY175 (left)

Aureolin PY40 (right)


Aureolin, Cobalt yellow PY40 was first sold as a paint in 1850. Winsor Lemon was introduced in 1996.

I had been aware of the defects regarding Aureolin when researching my book Color Right from the Start in 1993. But because Aureolin-PY40 received an endorsement by the ASTM- the American Society for Testing and Materials- as a recommended pigment I felt that my research must be flawed and not the ASTM’s! I reasoned that perhaps my negative results were due to the extreme heat or humidity in Texas for instance? However, when testing Aureolin PY40 for my book Hilary Page’s Guide to Watercolor Paints and its FREE online updates I found in ALL nine brands that use the pigment, that the paint turned brown and faded.

I contacted the chemists from two leading paint manufactures and told them of my findings. They concurred with what I was saying- that Aureolin is a defective pigment. One said that the pigment even turns brown in its dry, powdered state! In addition the pigment has a tendency to react with the medium in some brands, causing the tube to explode. To crown it all the paint is very expensive! We made a concerted effort to have the ASTM re-test Aureolin. But to date this has not been done. It should be noted that although the ASTM subcommittee that handles artists’ paints is manned by professionals in the field, they nevertheless are volunteers!

The actual color of Aureolin is wonderful. As a “warm” lemon it is the color of the standard primary yellow. This color is orange biased at full strength meaning that it will mix with reds to produce bright orange colors. It is green-biased in tint meaning that it will produce fresh, vibrant greens when mixed with blues and phthalo greens. Until recently there was no pigment available to match Aureolin’s “warm” lemon, two-tone color qualities: PY3 Hansa Lemon is too green biased and PY97 Hansa Yellow is a little too orange biased.


In 1996 a new pigment appeared in artists’ paints that is the perfect match for the “warm” lemon color of Aureolin and it’s cheaper too!. This pigment is PY175, a lemon Benzimidazolone as in WINSOR LEMON (Winsor & Newton). The same color is in Cotman’s Lemon Yellow Hue PY175 or Permanent Yellow Lemon PY175 (MaimeriBlu) or (Schmincke’s) Chrome Yellow Lemon (no lead) Any paint made with PY138 is also the same “warm” lemon color as Aureolin.

A few brands list an “Aureolin Hue” or “Aureolin Modern”. Usually the manufacturers get the substitute pigment wrong. PY97 or PY151. are too “warm”. Hansa Lemon PY3 is too green biased to mix to produce bright oranges.

Without a doubt PY175 as in Winsor Lemon is the perfect substitute for Aureolin, and cheaper too!