I recently came across this great experiment that was shared on the Artist’s Network Wetcanvas forum. It was an experiment carried out and shared by artist Ben Sones:
One of my medium yellowing tests–this one has been stored in the light (on the wall of my studio, where it receives daily north light) for about three years. These are swatches of straight medium on a piece of Arches Huile (sized) oil painting paper:
The mediums are, starting on the top left:
Gamblin Galkyd Lite
Gamblin Solvent Free Fluid
Winsor & Newton Liquin Original
Winsor & Newton Liquin Fine Detail
Graham’s Walnut Alkyd
Winsor & Newton Damar
Groves Amber Medium
Studio Products’ Mastic
Gamblin Cold Pressed Linseed Oil
Graham’s Walnut Oil
Winsor & Newton Stand Oil
Holbein Sun-Thickened Linseed Oil
Blue Ridge Sun-Thickened Linseed Oil
Studio Products’ Black Oil
Holbein Sun-Thickened Poppy Oil
Gamblin Stand Oil
Mixture: 50% W&N Stand Oil + 50% Graham’s Walnut Alkyd
Mixture: 50% W&N Stand Oil + 50% Gamblin Solvent Free Fluid
Winsor & Newton Drying Linseed Oil (linseed + manganese drier)
Mixture: 50% W&N Drying Linseed Oil + 50% W&N Stand Oil
When I first made the sheet, the Groves Amber was, by far, the darkest swatch on the sheet. Over time, it has stayed basically the same, while some of the other swatches have darkened a bit, particularly the sun oils, the solvent-free alkyds, and the black oil. The black oil has actually almost “caught up” with the amber, but not quite. They look similar in this photo (it’s hard to eliminate all glare and provide completely even lighting), but in person, the amber is definitely darker. Just a bit, though.
However! One thing this test doesn’t highlight is the fact that, like paints, different mediums actually have different “tinting” strengths. So the colors you see here are really only half the story. For example, on this sheet, the sun thickened oils look like they are almost as dark yellow as the amber medium. In practice, though, the amber medium has a considerably higher “tinting strength.” If you add it to some titanium white paint, it turns the paint noticeably oranger. If you add the same amount of sun thickened oil to some titanium white paint, it sort of disappears into the paint and doesn’t affect the color much at all. When stored in the light, at least–in dark storage, sun-thickened oil will yellow paint noticeably.
Linseed oil gets more of a bad rap for yellowing than it deserves. Probably because many people who test for yellowing store their samples in the dark. Dark storage aging is a pointless test, IMHO (though I do have a similar sheet that I keep in a drawer). Yes, linseed oil-based mediums yellow considerably in the dark. But that doesn’t really represent the typical display conditions for a painting, and the yellowing caused by dark storage is reversible. So it’s not a thing that I worry about. In my light-storage tests, linseed oil actually tends to yellow a little bit less than walnut oil, over time.
Graham’s Walnut alkyd has a bit of a bad rap for yellowing, but in my tests, it is almost indistinguishable from straight walnut oil in terms of yellowing. The alkyd is a touch darker, but it’s close. Both yellow a fair amount, but as with sun-thickened linseed oil, it’s not particularly noticeable when the mediums are mixed into paint.
Alkyds generally seem pretty good when it comes to yellowing. The “solvent free” variations (Graham’s Walnut and Gamblin’s Solvent Free Fluid) tend to yellow more than the traditional alkyd mediums. Liquin Original was the best performer, yellowing almost not at all.
The 50/50 mix of a solvent-free alkyd with stand oil (Graham’s Walnut Alkyd + Stand Oil is a favorite mixed medium of mine) yellows a little bit on this sheet, but is basically non-yellowing when mixed into white paint–even when stored in the dark. This mixture performs a lot like a straight sun thickened linseed oil–viscous and leveling, but with more flow than straight stand oil–and generally dries overnight.
Top five least-yellowing: Damar is easily the least yellowed sample on the sheet, in that it hasn’t yellowed at all (in light storage, or in dark storage). The mastic hasn’t yellowed, either, but was very slightly more yellow to begin with, right out of the bottle. It places second. Winsor & Newton’s Stand Oil comes in third, followed very closely by Liquin Original, followed by Gamblin’s Stand Oil.
Stand oil is amazing. The Winsor & Newton stand sample has yellowed basically not at all–even on my dark storage sheet. The Gamblin Stand Oil sample is a touch yellower; Gamblin’s stand oil seems to be a lower quality product in general, and I wouldn’t recommend it. The bottle that I have was clear when I bought it, but now is full of bits of floating mucilage that have separated out of the oil over time (see my review for Blick’s for more details). My bottle of W&N Stand, despite being years old, is still crystal clear.
The only mediums on this sheet that I would specifically recommend against are Black Oil and Groves Amber. Both are just too dark and yellow/orange, even when mixed into paint. The sun thickened linseed oils are kind of borderline–personally, I used to use sun thickened oil a lot, but this test actually convinced me to start using stand oil instead.
Hopefully that will be helpful to someone.