Robert Phillip Jones
Posted on Thu 06 Jul 2017
Partly because it's one year since I last posted a blog, and partly because I don't want to clog up the forum with things not everyone will want to read, I thought I'd attack the whole business of solvents and mediums in oil paint.
I have a Facebook account, and belong to several art groups there. An increasingly common issue is concern about using solvents, and adding oil to oil paint. This has especially come about since the advent (or return) of Walnut Oil as a painting medium - I'm seeing posts from beginner artists, and also more experienced ones, who are horribly confused about what thinning oil paint actually means, and are running into trouble because their paintings are looking like oil slicks.
The answer would, you would have thought, be obvious. If your oil paint is too oily, either you're using paint which requires a lot of oil to be milled adequately in the first place, or you're adding far too much additional oil. Walnut oil in particular is not a light, evanescent oil which will thin your paint and allow it to dry quickly - it's almost the exact reverse. When adding it to the paint, why are you doing so? Is it because you think you should? Do you believe this what thinning paint means? Are you under the impression that it will protect your paint film? You shouldn't; it doesn't; and it won't necessarily do so.
Adding any oil will increase the tendency to yellowing later on. It may be that Walnut Oil or Poppy Oil yellow less than Linseed, but that doesn't mean you should always use them - because they're extremely slow-drying. Add them to a paint which is slow-drying in the first place and you'll have a paint film that remains tacky for weeks or months, or even never really dries at all. One person writing on FB told us she had glazed Rembrandt Translucent White (may be Transparent rather than the word I used) mixed with Walnut Oil, and was surprised that it was still tacky just two weeks later. Well - it would be. Zinc White is a very slow drying colour, and transparent white is likely to be Zinc; add a slow-drying oil ... you'll still be waiting for it to dry come next Christmas.
Thinning paint, if that's what you want to do or need to do, does not involve adding extra oil: that's not thinning it, it's making it "fat" - i.e. it directly disregards the one rule in oil painting you really can't ignore: paint fat over lean, never lean over fat. "Fat" - which is a word which confuses many - doesn't refer to the volume of paint so much as the oil used with it. Think of fat as oil - and save yourself an unpleasant painting experience, and future cracking.
Do you need to add solvents (like Turpentine or Odourless Mineral Spirits [OMS]) or oil at all to oil paint? To make the paint capable of fine detail, which you might want to add, crucially, to the end of the painting process, yes you sometimes do. But why not try doing without? All too many of us just fill our double dipper with turps on one side, oil on the other, and automatically add the solvent to the early layers, and oil to the later ones. If we could learn to use the solvent or medium when we REALLY need them, and use the paint out of the tube instead, it would solve all of this, and minimize the amount of additive. We do seem so often to forget that the paint is ALREADY mixed with oil - if you don't have to add oil, just don't. If you're not covering a large area with colour to stain the canvas before adding thicker paint, why not lay down your base colour, leave it to dry, and then come back with paint direct from the tube? Indeed, why apply a base stain at all - I know it helps - and why use more than a thimbleful of spirit to thin it?
In my e-book, Oil Paint Basics, which was intended mainly for beginners but also would-be improvers, I recommended using a medium that is part Turps (and I prefer genuine Turpentine because of its resinous base) and part Linseed Oil. I didn't go much further than that, because this is a good basic medium, and it was basics I was trying to deal with. There are of course many other mediums - Winsor and Newton make one; they also make Liquin in all its various forms, which is an alkyd medium which promotes drying; there's Stand Oil and Sun-thickened Linseed Oil - a good medium, which can be cut with Turps; then you've got Poppy Oil, straight Linseed Oil, Walnut Oil, and a quite horrible medium still sold by some makers which calls itself Copal Oil and one I'd suggest you avoid either in its original form, if it can still be obtained, or in the forms now available (it darkens paint over time). There are many others, some of which claim to be the secret recipes of the Old Masters (they never are, and wouldn't necessarily be desirable if they were) .... and there are gels, waxes, mediums containing dammar or other varnishes. You can see why I recommended sticking to the Linseed Oil/Turps mixture, I think - any beginner would be horribly confused by that lot.
Whatever you use - and waxes, and varnishes in mediums are best avoided - do just ask yourself if you really need to use it at all. This is easy for me to say, I know, because I tend to paint fairly small and rarely need to cover very large areas; it's also true that some surfaces are more porous than others and need a little medium to keep the paint moving. Even so - it is not a good idea to flood every mix of paint on the palette with oil or any medium, particularly if painting alla prima rather than in discrete layers. Try doing without, not as a penance or discipline, use medium when you need to - but have a go at severely rationing it: tell yourself it's a very expensive extra ingredient which it would be foolishness itself to use profligately: and let me know if you get on more easily without it than you did if you previously used it automatically.