Linseed oil is a good medium for adjusting the consistency of oil paints.
Compared to walnut oil, “linseed oil dries better and faster, and makes stronger, more durable paint films. For multi-layer techniques, linseed oil paints are best for all but the final layer. Walnut and safflower oils yellow less, so are often used as binders for blues, where yellowing would be more noticeable than it would in other colors.”
The yellowing of linseed oil paints is a temporary condition that reverses with exposure to light.
Alkali-refined linseed oil is good. So is cold-pressed linseed oil, and perhaps if it’s water-washed it’s even better. Procedure for water-washing linseed oil is in my book, or you can buy some already done that way by Rolf Hareem of RGH oil paints.
Linseed oil is usually available in large quantities at hardware stores and paint stores less expensively than in art supply stores or health food stores. In health food stores it’s called Flax Oil or Flaxseed Oil, for use as a nutritional supplement since it’s high in omega 3 fatty acids. But if it has vitamin E or other preservatives in it, it’s not suitable for art purposes because it won’t dry, so read the label before you buy.
Note that hardware store linseed oil is best used only for brush cleaning, as it’s less pure than artist-grade linseed oil, and therefore more likely to darken as it ages. So don’t use hardware store linseed oil for a painting medium or ingredient in a medium.
There are no significant drawbacks to walnut oil, other than it being somewhat inferior to linseed oil in film strength. The handling characteristics are more “short” than linseed oil. See page 122 of my book for an explanation of long versus short oils.
In response to a Facebook member who wants to use walnut oil as a medium for underpainting, Virgil responds:
“Ideally, no medium at all should be added to paint for underpainting. Walnut oil is not a good choice for two reasons; one, it forms weaker paint films than linseed oil, and two, it dries more slowly than linseed oil. The most structurally solid underpainting would have the leanest paints as its basis: lead white in particular, for its leanness, its fast drying, and the fact that it forms the most durable paint films of all oil paints, and confers that quality to all the paints used in conjunction with it. Tint it with high tinting strength colors such as the Mars (synthetic iron oxide) colors, or pigments that are lean by their nature, or both, all bound with linseed oil. Walnut oil is all right for the final layer.”
A Facebook member asks: “From the standpoint of constructing an oil painting soundly, is there a problem with using both walnut oil-based and linseed oil-based paints in various layers (including linseed over walnut) within the same painting?” Virgil replies: “On a rigid support, it isn’t as critical an issue as it would be on stretched canvas, but ideally walnut oil paints should be introduced only near the end of the process, after the bulk of the painting has been done with linseed oil paints, if you’re using a multi-layer technique.”
Poppy oil is a slow drying oil that produces structurally inferior paint films compared to linseed oil.
Balsams, including Turpentine
Damar or Dammar Resin
I’ve tried copal and amber mediums in the past, and found they were more compatible with painting on smooth panels in small sizes using soft-hair brushes, rather than larger paintings on canvas that has more texture to it. For the latter, these resins add too much gloss to the paint, which makes large paintings harder to read if they’re not lit from high above. I found that in order to avoid extremes in variations of surface gloss, I had to eliminate resins and polymerized oils from my paints to reduce the glossiness of those passages, and umbers from my palette to eliminate or reduce the dry-appearing patches commonly referred to as “sinking in.” My medium now is just water-washed, sun-bleached linseed oil, and not very much of that.
There is also darkening of the natural resins to consider, as it’s irreversible, and embrittlement, which would be less of a concern on a rigid panel than on stretched canvas.
I glue my canvas to a panel, but I don’t see a great need for copal or amber resins in my own work. I do add a bit of copal to the paint with which I sign my signature, because I like “long” paint for that, but otherwise I don’t bother with it.
A Facebook member asks about a Amber medium on the market made by Blockx and promoted as one of the secrets of the Old Masters. Virgil responds: Blockx’s information that forms the basis of their assertions is over 100 years old. We might entertain a degree of doubt when a company that wants to sell us a product tells us how wonderful it is. They might not be totally objective in their evaluation. Just a thought.
My concern with the Blockx amber medium is that it’s made with poppy oil. Poppy oil is a slow drying oil that produces structurally inferior paint films compared to linseed oil.
George O’Hanlon of Natural Pigments adds: “If you read my article on resins I do not recommend resins in oil painting but, if resins are used, hard resins such as alkyd, copal and possibly amber are better than soft resins such as dammar and mastic. However the main issue with resins is their differences in solubility and drying mechanism. They complex the paint film and should only be used sparingly, if at all. There is little evidence of the use by the old masters and there is even less knowledge of how it performs with age.”
Liquin is an alkyd medium made by Winsor & Newton that contains both alkyds (modified oils that dry faster than regular vegetable oils) and solvents. It should not be used as a varnish.
Virgil’s assessment: Liquin is a good medium if you want fast drying and your working space is well ventilated. It contains a volatile solvent, so there are vapors to consider. It isn’t intended to be an impasto medium for thick painting…
I see no problems in it as far as the structural soundness of the painting itself is concerned… the solvent in the Liquin give off vapors that can be harmful to breathe, however, which might or might not bother you right now, but could cause health consequences at some point after longer exposure. If you’re painting outdoors it shouldn’t be a problem, but otherwise make sure there is good ventilation in your workspace, and do everything you can to keep the solvent vapors there down to as low a level as possible.
My top recommendation is to use no solvents or mediums that contain solvent. If the paint is too thick for good control, as it is with some brands, a very small addition of linseed oil mixed into the paint on the palette thoroughly with a palette knife should correct that problem, and if it doesn’t, a change of brands might be in order.
In response to a Facebook group user’s concerns about older bottles of Liquin appearing too dark, Virgil writes: “Liquin doesn’t darken in paint any more than linseed oil does, unless too much is added to the paint, but the darkening of Liquin and also of linseed oil is not enough to cause any legitimate concern. The yellowing/darkening seen in short-term aging reverses with exposure to light. The secondary yellowing that occurs after long aging is so slight as to be negligible, as long as the ratio of medium to pigment is not excessive.”… “It’s not enough to affect the appearance of the paint as long as the mixture is 15% or less Liquin/85% or more paint. 10% Liquin/90% oil paint would be still better.”
Used without paint in it, as a varnish, Liquin will be very difficult to remove if or when it ever darkens (which it will) or develops some other problem that interferes with the viewing of the painting or alters its appearance in some way. The solvents that will be needed to remove it will take the paint off too. Winsor & Newton advise against using Liquin in that way.
Odorless Mineral Spirits (OMS)
Spike Lavender Oil
Spike lavender oil is a solvent, not an oil; it thins oil paints, mediums and varnishes in the same way that odorless mineral spirits (OMS) would do. It is a strong solvent that dries slowly.
Beware of art suppliers who claim that spike lavender oil is safer than other solvents or even non-toxic. The effects of inhaling spike oil for artists are unknown; precautions should be taken. Use spike lavender oil with adequate ventilation and/or protective gear.
Keep in mind that it is not necessary to use any solvent in order to paint well with oils.
Everything you need to know about lavender and spike oils: Natural Pigments article.
The bottom of the article discusses the historic use of spike oil in art.
Virgil supports the advice of expert conservator, Kristin DeGhetaldi, PhD, who worked in the Conservation Department of the National Gallery in Washington DC before starting the MITRA website. She has written: “Spike Lavender oil contains a number of terpenes and other materials with the same health code rating as OMS. Spike lavender oil is much slower evaporating so it is more likely to bite into underlayers….the only reason to use it instead of OMS is if one likes the smell…if you are however trying to dilute things like stand oil or resinous medium (which is not particularly encouraged) some grades of OMS will not work as well compared to MS, Turp, and/or spike lavender. If you are looking for something that is less aggressive at thinning oil paint OMS is probably the best option.”
More from Virgil: There are some products being marketed as lavender spike oil for use in oil painting that have other ingredients in them that might not actually qualify as non-toxic, so I would not be too eager to accept salesmen’s claims of wonderful properties, health safety in particular. We should not assume that things that have not been tested for their health effects and declared toxic are therefore necessarily non-toxic. I would expect any volatile solvent’s vapors to pose health risks.
In any case, it isn’t necessary to use any solvent in order to paint well with oils.
Another resource: Tad Spurgeon’s article reviewing the available products on the market.
Virgil also recommends avoid using varnish that contains lavender oil. (Example: Chelsea Studio Classic Lavender Damar Varnish). The lavender oil is a strong solvent that dries slowly. There is the chance that it could eat into the paint, and possibly smear it or remove some of it unless the paint is well cured before the varnish is brushed on. Wait at least one year after the last brushstroke is dry before applying it.
Citrus Peel Solvent