Editor’s note: Mediums and solvents are covered in Virgil’s book, pages 132 -142.
All oil painting solvents are inhalation hazards, no matter how ‘non-toxic’ they claim to be. Use with ventilation.
It really isn’t necessary to use turpentine or any other solvent when painting in oils. Solvents weaken the binding power of oil paints, and the vapors are harmful to breathe. Your painting and your health will fare better if you adapt to solvent-free oil painting.
I’m not advocating for solvents of any kind. I’m advocating painting without solvents, in the interest of the longevity of the painting and the health of the painter and whoever else shares the air in the painting space.
I’ll reiterate that it is not necessary to use turpentine, or mineral spirits, or spike oil, or citrus peel solvent or any kind of solvent when painting with oil paints.
Two good reasons not to thin oil paints with solvent:
1) you and all who share your air space are spared the potential harm to your/their health that inhalation of solvent vapors could cause, and
2) solvents mixed with oil paint weaken the binding power of the oil binder, thus increasing the likelihood of problems developing in your paintings at some point in the future.
If you find your paints too thick for good control, mix in a tiny drop of linseed or walnut oil to each pile of paint on the palette, and mix it in thoroughly with a palette knife. The longer you work it with the knife, the softer it will become, so not much oil is needed.
Solvents are not needed to clean brushes. To clean brushes while painting: have two jars of linseed, walnut, or safflower oil ready for that purpose; wipe the brush on a rag or paper towel, rinse in the first jar, wipe again, rinse in jar #2, wipe again, and the brush is ready for a new color. Use the same procedure after the session is over, then wash each brush with soap and water.
Odorless Mineral Spirits (OMS)
Gamsol is the mildest kind of odorless mineral spirits.
You can use it to clean an oil painting prior to varnishing by gently wiping the surface of the painting with a soft cloth very lightly moistened with it. There should be no adverse effects from this procedure if the painting has had at least six months to cure. This is not theory or guessing on my part, but is based on actual experience doing it at the suggestion of Ross Merrill when he was Chief of Conservation at the National Gallery in Washington DC.
The solvent that speeds drying is gum turpentine. Mineral spirits does not, nor does spike lavender, which is a slower drying solvent. However, they are all best left out, because they can compromise adhesive strength and film strength of the paints to which they are added.
What effect does using gum turpentine have on oil paint?
Gum turpentine will thin oil paints, and is used in that way by many painters; however, thinning oil paints too far will weaken the adhesive strength and potentially compromise the adhesion of the paint to the ground or previous layers. It can also remove dried oil paint that is not well cured. Mixed with oil paints while painting, it’s reported to increase the tendency to yellow with age. It does speed up the drying slightly.
In the context of dissolving varnishes: gum turpentine dissolves Damar varnish.
If you feel you have too thick a coat of varnish on your painting, you can thin it out by brushing over it with the appropriate solvent, and then again with dry brushes while it’s wet. Which solvent is the right one to use would depend on what resin the varnish has in it. If it’s damar, then gum turpentine would be the right solvent. If it’s an acrylic MSA varnish , mineral spirits is the correct solvent; if regalrez (Gamvar, etc.), then odorless mineral spirits will do it.
Another reply to a reader who wants to remove Damar varnish from an old painting before touching it up again:
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.