This is a question that comes up a lot in beginning oil painting classes: “Can’t I use olive oil instead of linseed? It’s much less expensive and I already have some! All oils are the same, right?”
Oils can either be drying, semi-drying, or non-drying. For the sake of this conversation, I’m going to lump semi-drying oils in with non-drying oils because they still don’t harden completely, which is what you want when oil painting. There are some nuances, however, in which occasionally a semi-drying oil will be mixed with a drying agent which makes it workable for oil painting (I’m talking walnut and poppy here) but to keep this conversation somewhat simplified, we’re going to just discuss drying versus non-drying oils.
Here are some examples of each type:
Linseed Oil (which is derived from flax and has many forms: raw linseed oil, refined linseed, varnish linseed, stand oil, blown/bodied/boiled oil, sun-refined or sun-bleached oil)
Tung Oil (used mainly for woodworking and not recommended for painting)
It can be a little confusing because all the oils are derived from some sort of natural source (flax, olives, various nuts, etc.), but some are better at drying into hard films than others. Non-drying oils are ones that you would eat or cook with and drying oils are ones you would paint with. Granted, there are certain walnut oils that are used in cooking, but they’re processed in a different way. Don’t ever use the same oil for both painting and cooking! Either your paint will run right off the canvas or you’ll make yourself very, very sick.
How do drying oils work?
The way that these oils dry is through a chemical process called “oxidation”. It’s different than evaporation, a process in which moisture is drawn out by exposure to air–think about watercolors. They dry by the process of evaporation. Exposure to air causes the water in the paint to dry up, essentially, leaving behind just the pigment on the paper. Oil paints work in a different way in that they don’t require air for moisture to be drawn out, but they do require exposure to oxygen in order to draw it in allowing for the oxidation process to begin and a film to develop or the oil to “cure”.
Here’s an example. I have a bottle of olive oil next to my stove. It has a cork top and an open pour spout so I can use it to dress salads/add a little bit of olive oil at a time to a dish. It’s constantly exposed to air, but never dries. This is a perfect example of a non-drying oil.
I also have a bottle of linseed oil in my painting supplies. It has an air-tight lid on it. When I put a bit of linseed oil into a cup to use as I’m painting, if I don’t clean the cup, the linseed oil will become sticky and start to develop a film over the top. That’s when oxidation is taking place.
If you have some oil paints in your house and read the label on the back, you’ll often notice that the pigments are mixed with either a drying or semi-drying oil (linseed and poppy are common). This is just a binder that allows the pigments to move when you’re painting with them (otherwise they’d just be dry, dusty pigments and those can pose serious health concerns when inhaled). If you’ve ever left a tube of oil paint with the cap off, you’ll see the oxidation process happen. The oil used as a binder will often harden, at least to some extent, so that you have to remove that bit or poke a hole in it in order for the fresh paint to emerge from the tube.
How are drying and non-drying oils different?
Other than the obvious that some dry and some don’t, there are a few other differences. Drying oils, used for oil painting, often go through a refining process to help prevent them from yellowing or discoloring your painting. Non-drying oils, or oils that you use in food, are refined to make them not only safe to consume but palatable (tasty!). Drying oils produced for use in art are specifically formulated for that purpose. Drying oils also have the capability to spontaneously combusting during the oxidation purpose. For instance, if you spilled a bunch of olive oil and used a rag to clean it up, then balled the rag up and put it in the laundry bin for a week, it would be fine. Oily, maybe a bit stinky, but fine. On the other hand, if you spilled a bunch of linseed oil and cleaned it up with a rag, and did the same thing–balled it up and left it in the hamper for a week–it’s VERY possible that it would burst into flames and take the rest of your laundry with it. This brings up an important note: if you do spill a drying oil and clean it up with a rag, soak the rag with water and lay it our FLAT to dry. Balling up the rag only creates more spaces for heat to build during the chemical reaction process by which it dries, making it more likely to catch fire.
What happens if I use non- or semi-drying oils in my oil painting?
Well, the paint will never cure and your painting could potentially develop mold. That’s basically the gist of it.
Are there any alternatives to oils?
Yes! In the last decade or so, drying oils are being replaced by alkyds or alkyd driers which are synthetic forms of drying oils produced specifically for art purposes and eliminate some of the uncertainties that come with drying oils. They are much less fussy to use and tend not to crack. For example, linseed oil is a very popular oil to use, but it tends to yellow over time, making it unsuitable for mixing with white or light colors. Poppy oil is paler in color, which makes it fine to use with white or light colors, but dries much slower than linseed. Both can cause your paint to crack if used incorrectly or in inconsistent mixtures.
If you wanted to use a mixture of linseed and poppy oil in a painting, you’d need to be very mindful about it. Because the drying times between linseed and poppy oil are different, you would need to remember which you put where and when. This can be a rather confusing endeavor, especially if you’re like me/most artists and work on multiple paintings at any given moment. Unless you keep extensive notes on exactly what oils/mixtures you used where and when, it’s easier to use an alkyd medium that replicates the look and feel of drying oils but without the bother. I used to be very old school about my oil paintings–mixing up little vials of differing types of oils/oil-solvent mixtures and keeping extensive notes, being careful to only place this here or there–but then I decided I’d rather give that energy to my painting and not the traditional mediums of old masters. To each his own, but for me, I think alkyd mediums are the way to go, especially if you’re a new oil painter. It eliminates worry and gives your brain a little more room to think about other things (am I using a cool or warm blue? Is this the right shape brush for this object? etc.). We recommend Neo-Megilp for our oil painting course, though Liquin and Galkyd are also great options.
If you want more information on specific mediums used for painting, check out this post:
In short, I would recommend you always use oils purchased from an art store–not a food store–for your use in oil painting.