Many tests in watercolor have contradicted the ASTM rating for this pigment, by showing a terrible grey color from what was originally a yellow. However, I have yet to find any swatches for oil paint testing with this pigment. I scoured Google and found only one person who said “Aureolin did what it always does — darken.”
I also remember reading, many years ago, people discussing various brands. Some believed that Grumbacher’s (at least historically) was lightfast, arguing that its darker color out of the tube related to its greater resistant to color change. I have used Grumbacher’s aureolin and it, indeed, is more of a medium-dark straw yellow out of the tube, versus the much lighter and more saturated paint I have seen from other brands’ swatches. The painting I used it on also didn’t show a color shift toward grey. It, though, wasn’t exposed to any strong sunlight.
I have created this post because, as with the other pigment I asked about, I can’t find any conservation literature about this pigment’s lightfastness. All I can find are various tiny bits, unsupported with charts/data, about how some pigment chemists didn’t believe it could be stable due to its odd (for a pigment) chemistry. I am wondering if it is lightfast in oils, particularly if it is kept out of bright sunlight (i.e. museum conditions). I also have read, I think, that it reacts with true emerald green but no one uses that anymore so that’s moot.
Does anyone know of any research into this pigment that would answer these questions? It seems that the matter of its use in watercolors has been thoroughly resolved. It turns grey. However, it oils, I am inclined to believe that if it isn’t exposed to much UV it will last long enough to be considered “lightfast enough” for serious oil painting, in a manner similar to quinacridone rose and carbazole violet.
— SRS
I’ve seen two samples of Aureolin oil paint turn grey, but only as tints with white. One was by someone else with a sample left outside under glass and another by myself about thirty years ago under shelter but outside and exposed to half day sunlight for a full year. My full strength sample displayed only the slightest of changes, if still visible. The cobalt yellow tint I considered a complete failure so have never used it since.
I imagine under museum conditions one would never live long enough to see any change though.
Marc.
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