Estimated reading time: 5 minutes
Walnut oil, for many painters throughout the ages, has been the more popular choice for oil painting for as far back as the Renaissance, when painters claimed that it produces less yellowing over time as compared to linseed or safflower oil. Additional claims are that it dries faster than other oils, and produces a softer, less artificial finish as compared to chemical blends, and can be used to wash paint off of brushes and other tools just as readily as paint thinners.
With all of these benefits, are there any downsides to using walnut oil as a painting medium? And, even more relevantly, can walnut oil be used as a painting medium when it comes to painting with water mixable oil paints?
The answer is, yes and no.
The only way to answer this question fully is to explore exactly what makes an oil so important to use when painting with water mixable oils, and why it is that some oil mediums are more popular to use with it than others.
Can I Use Any Walnut Oil?
When it comes to painting mediums, it may be tempted to skip the bill of other artisan painters and reach into your grocery store shelf for that bottle of walnut oil. But this would absolutely not work as you’d like it to when it comes to oil painting. Walnut oil mediums are notoriously finicky, needing to be stored carefully in the refrigerator in order to prevent it going rancid as much as possible. This is usually controlled in cooking walnut oil through various natural additives and vitamins, which make for great cooking oil, but very poor painting mediums. Especially since those same additives may ruin your painting experience, and will certainly add hours to your waiting time between layers, since they’ll increase the drying time of already-slow oil paints.
When it comes to mixing medium into your oil paints, it is important to shop for the correct materials, and doubly so when it comes to investing in a medium which can be as expensive and as quick to spoil as walnut oil.
When it comes to acquiring water-soluble mediums out there on the market, you’ll find that it is much easier to find linseed and safflower-based oil mediums than it is to find ones based on walnut oil, though this isn’t a reason to not use walnut oil as a medium. The important factor when it comes to selecting a medium to work with when using water mixable oil paints is whether an oil medium contains solvents – usually a turpentine mixture – or not. This is because of the way that water functions as a solvent in its own right when painting with water mixable oil paints.
The reason that water mixable oils paints (sometimes called water-washable paints for this exact reason) are so much safer than traditional oil paints is because they do not require the use of noxious solvents, such as various turpentine mixtures. These solvents, sometimes only referred to as turps, release fumes as they dry, which are dangerous to breathe in large quantities, especially over a long period of time and for children and small animals. Turpentine is also a flammable liquid, and its fumes make for a fire hazard, meaning that you should not paint using traditional oils in your apartment or small, confined space. Always paint in an art studio with necessary protections and a ventilation system, or even better, outside with them. All of the risks that we outlined here are simply not a factor with water mixable oil paints, because of their dependence on water as a mixing liquid. The water evaporates off of the paint as regular water vapour, which is safe to breath and should pose no threat to you or anyone living with you, though the paints themselves should still be kept well out of reach of children or animals.
It is important to remember that turpentine is a much less liquid substance than water, which makes water mixable oils much runnier by nature than traditional oils. In order to get the same texture and impasto painting style as traditional oils, as well as to maintain the gloss of the finished piece, since water-based paints dry into a much more matte, drier finish, it is important to use mediums correctly, and to gradually increase the amount used with each subsequent layer. This will lengthen the drying team significantly, but this is not necessarily a bad thing – a longer drying time gives you longer to work on a piece, and much more time to add surface details, textures, peaks and rises to the surface of the paint that will be seen from the outset.
So, Why Not Use Walnut Oil?
Walnut oil-based mediums are rare and are not frequently made for water mixables, which makes using them with water mixable paints a bit of a trial and error process. But this does not mean that you cannot use them altogether. The most important thing to look for is walnut oil mediums that are either completely pure, without any additives. Or at least without any additives that are considered solvents, such as alcohols or turpentines, which may compromise the integrity of the water mixable oil paints.
When searching for these purified walnut oils, you should not worry about buying a large amount. Even when it comes to traditional oil painting, most painters use walnut oil sparingly, only for the final layers, using more common and flexible mediums for the layers that do not require as much consideration.
Because of how finicky and particular walnut oil is, you should only use a small amount for the final layers, especially the finishing brushstrokes of the painting, those most exposed to light and thus as highest risk of yellowing. When used in these small amounts and without other solvents, water mixable oil paints can be used with walnut oil mediums without there being any problem. But, for safety’s sake, I recommend using it gingerly and experimenting frequently to see if the resulting paint layer is right for the painting you are using it for.