MITRA Forum Question Details

​Williamsburg explained this in a 2015 bulletin: http://www.williamsburgoils.com/blog/?p=220

"...a transparent version of  PY83, a diarylide yellow that in its opaque form is among the most lightfast yellows available. However, based on the test results, this transparent version would need to be rated as Fair, or the equivalent of ASTM III, the same category as Alizarin Crimson. "

Hi -

So glad you asked this question as it definitely IS confusing and having a chance to clear up the situation is always welcomed. Plus, we also happened to write an article, beyond the blog post that Matt Kinsley mentions, that goes into it this and other changes in some detail:

Beauty and the Best: Wrestling with Changes in Williamsburg

I would also want to make sure if you do have a tube listing it as PY83 HR, as that would be a mistake and we would certainly want to know about it. And sadly we are aware that the mislabeling of a transparent version of PY83 as HR is not uncommon and it is always worth double checking. To just touch base on the main point of the article, here is the most relevant passage:

"All of which brings us to the last three colors: Alizarin Orange, Alizarin Yellow and Indian Yellow. Unfortunately, the pigment at the center of these, a type of Diarylide Yellow, comes in various forms that all share the same Color Index Name of PY 83. As you can imagine, this can lead to some confusion when assigning a rating. The opaque version, which carries the additional designation ‘HR-70’ in its chemical description, has excellent lightfastness and is on the ASTM list of rated pigments. However, our testing showed that the transparent version Williamsburg had chosen could only be rated as Fair, or the equivalent to ASTM III. And here lies the crux of our quandary. These three colors have had exceptionally long and beloved histories within the Williamsburg brand, going back to its earliest days. Many painters who have used Williamsburg throughout these decades are passionately connected to their uniqueness, so a sudden change would be felt as particularly disruptive. And as if to confirm that, when searching for an alternative pigment we could use, we simply could not find anything with the same brilliance, transparency, and glow. So a choice needed to be made: dramatically change the look of these colors, discontinue them, or keep them as part of our offerings but clearly label their lightfastness as Fair, a rating similar to Alizarin Crimson."

And here is the table of data that we show, which might be somewhat reassuring.  ASTM Lightfastness I allows up to 4 Delta E of change, and ASTM LF II allows 8. However, ASTM states - and we think fairly - that you must label the tube with the lightfastness of the weakest pigment. Thus why we list them as fair. But because they are mixed with very lightfastness pigments in the blend, they are just a touch over LF II in the very harsh South Florida Test, and would qualify as LF II in the indoor accelerated Xenon testing. And they certainly do better that Alizari Crimson, which many artists have come to accept.

​Thanks so much Sarah.