Hello MITRA,
I received a gift of half a dozen tubes of pigment-rich professional paint with seemingly no strange fillers. However, two tubes have questionable pigments: PY3 and PR112. I would feel bad not finding a use for them, so I wonder if the suggestions from this post could apply to oils.
From https://www.artcons.udel.edu/mitra/forums/question?QID=776:
“If you mix a small amount of Gamblin Etching Ink Yellow Ochre (PY43), you might increase lightfastness (Iron oxides are used with an organic pigment in the paint industries). Of course, it will affect the chroma and lightness of Hansa Yellow Light (PY3).”
I also found the assertion that “adding Iron aids in increasing lightfastness for fabric dyes” at https://botanicalcolors.com/botanical-colors-how-tos/how-to-use-iron-powder-ferrous-sulfate/.
Handprint.com lists PY3 + PY42 (aureolin [hue], Holbein, in watercolor) as the most satisfactory PY3 in the listed lightfast tests ( https://www.handprint.com/HP/WCL/waterfs.html).
If you feel this tactic could work with oil paint, could the protective measure of “adding iron,” perhaps in a 1:1 ratio, also work with Napthol Red PR112 using Red Iron Oxide PR101? Or would I just have the ultimate end result of pure Red Iron Oxide after 50 years?
Also, does anyone know if PY3 ever stabilizes in its color after light exposure?
I see it darkens and browns, but does it stabilize into a greenish-brownish dark yellow after a set amount of months or years and then remain that way, or does this process last indefinitely, leaving a strange dark green-brown after 70+ years? If that’s the case and PY3 is rather useless as a yellow in the longer term, maybe the safest way would be to use it as an “extender” or sorts for dark brown shades, or perhaps a dark Chrome Oxide Green?
Thank you in advance for any information you could provide.
My advice is to replace PY 3 with a pigment that is more reliably lightfast. Iron oxides are dull. Adding those to bright pigments like PY 3 and napthol reds contradicts the main reason for using those questionable pigments in the first place. I also think the only reason the Holbein mixture did better in the testing was because the iron oxide wasn’t changed — not because the PY 3 was stabilized by it significantly.
Napthols are dye-based. Although some of them are more lightfast than others, their chemistry is not among the most stable of organic compounds.
PY 3 can be replaced by PY 175. Or, if one doesn’t mind the opacity, by PY 184 and PY 35 — both of which are more lightfast than PY 175. PY 35 can’t be used when exposed to weather (murals).
PR 112 can be replaced by pyrrole reds: PR 254, PR 255. PR 168 can also be found with good reliability if it is produced correctly. It can be produced to be more transparent than the pyrroles but also has a semi-opaque form. Handprint’s data may underestimate the lightfastness of PR 168 and overestimate the lightfastness of PR 242, although there can be variance in the lightfastness of different companies’ products using the same codes. One industrial manual describes PR 168 as being one of the top organic pigments in lightfastness.
I am not an art conservation expert nor a professional chemist so take what I have to say on an advance amateur’s basis.
— SRS
