Quick answer: You should not use cooking oil as a medium in oil painting. Most kitchen oils (olive, canola, vegetable, peanut, corn) are non-drying or semi-drying: they never fully harden, so paint mixed with them stays soft, attracts dust, yellows, and can eventually go rancid or bead on the surface. Oil paint relies on drying oils such as linseed, walnut, safflower, and poppy, which oxidize into a solid film. Cooking oil is fine for one job only: cleaning oil paint out of brushes before washing with soap, where it is wiped away rather than left in the painting.
Can you use cooking oil for oil painting? The question is reasonable. Linseed oil comes from flax seed, walnut oil comes from walnuts, and both can be found in the grocery store next to the olive oil. If artists’ oils are food oils, why not the reverse? The answer hinges on one chemical property that separates a painting oil from a frying oil, and once that property is clear, the rest of the question answers itself.
This explainer covers what a drying oil is, which oils qualify and which do not, what actually happens to a painting made with cooking oil, the special cases (sunflower, walnut, and food-grade linseed), the one job cooking oil does well in a studio, and the proper cheap alternatives. Oil’s chemistry is also the root of its slow drying and its handling differences from acrylic, which the oil versus acrylic painting comparison explores in depth.
What makes an oil a “drying oil”
Oil paint does not dry by evaporation. The oil in it reacts with oxygen in the air and the fatty acid chains cross-link into a tough, solid polymer network. This is called oxidative drying or curing. It takes days to become touch-dry and months to years to complete, but the result is a durable film that holds pigment in place for centuries.
Whether an oil can do this depends on how many reactive double bonds its fatty acids contain. Chemists measure this as the iodine value; the higher the number, the more readily the oil oxidizes and hardens.
| Category | Iodine value (approx.) | Examples | Behavior in paint |
|---|---|---|---|
| Drying oils | Above ~150 | Linseed (flax), walnut, poppy seed, perilla, tung | Cure to a solid film; suitable as binders and mediums |
| Semi-drying oils | ~115–150 | Safflower (high-linoleic), sunflower (high-linoleic), soybean, corn, grapeseed | Dry slowly and incompletely; some (safflower) are used commercially with care; most kitchen versions are unreliable |
| Non-drying oils | Below ~115 | Olive, canola (rapeseed), peanut, high-oleic sunflower and safflower, coconut, palm, mineral oil | Never harden; remain liquid or sticky indefinitely |
Linseed oil, with an iodine value around 170 to 200, is the standard binder for artists’ oils because it dries fastest and forms the strongest film. Walnut and poppy dry more slowly and yellow less, so they appear in whites and pale colors. Everything in the kitchen cabinet except linseed and walnut falls into the semi-drying or non-drying groups.
Can you use cooking oil for oil painting: what actually happens
Suppose a painter thins or extends oil paint with ordinary vegetable oil, canola, or olive oil. The likely sequence is this:
- Wet handling seems fine. The oil thins the paint and it brushes smoothly. Nothing looks wrong on day one.
- The surface stays tacky. After a week, the linseed oil already in the paint has begun to skin, but the added cooking oil has not. The surface feels soft and picks up fingerprints and dust.
- Oil separates. Non-drying oil has nowhere to go. It can migrate to the surface and bead, or soak into the ground and leave a dark halo around the paint.
- Yellowing and darkening. Food oils are refined for cooking, not for color stability. They tend to yellow and darken significantly as they age and oxidize partially.
- Rancidity. Food oils contain free fatty acids and impurities that break down. Over months a painting can develop a rancid smell.
- Permanent softness. Because the film never fully cures, the layer stays vulnerable. Later layers painted over it (fat over lean reversed) are likely to crack, and varnishing a surface that is still soft traps the problem under the varnish.
The painting may survive as an object, but it will not behave like an oil painting, and its appearance will keep changing in ways you did not intend.
Can you use sunflower oil for oil painting?
Sunflower oil gets asked about more than the others because sunflower is a semi-drying oil in its traditional form and has been used in some commercial paints. The complication is that modern grocery sunflower oil is often “high-oleic,” bred to resist oxidation for a longer shelf life and better frying. Resisting oxidation is exactly the opposite of what a painting oil needs to do.
So the answer splits:
- High-linoleic (traditional) sunflower oil can partially dry over a long period. It is a poor substitute for linseed: slow, weak film, uncertain long-term behavior. Some manufacturers have used refined sunflower oil as a component in paints, but as a controlled, refined ingredient rather than a kitchen bottle.
- High-oleic sunflower oil, which is what most supermarket bottles now contain, is effectively non-drying. It will not cure.
Since bottle labels rarely make the distinction obvious and food-grade refining differs from artist-grade processing, kitchen sunflower oil is not a reliable medium. The same applies to safflower oil: artist-grade safflower is a legitimate slow-drying medium used in many whites, but the high-oleic safflower oil sold for cooking is non-drying.
What about walnut oil and linseed oil from the grocery store?
These two are genuine drying oils, and the question becomes about refinement rather than chemistry.
Walnut oil. Food-grade walnut oil is a drying oil and some painters do use it, particularly cold-pressed, unflavored varieties. Caveats: it may contain antioxidants added to extend shelf life, which slow drying; it is not filtered to artist standards and can carry impurities that affect clarity over time; and it goes rancid in the bottle faster than artist-grade walnut oil. Artist walnut oil is processed to remove these variables. It is usable in a pinch and is a far better choice than any other kitchen oil.
Food-grade flaxseed oil. Chemically the same as linseed oil. But the flaxseed oil sold as a dietary supplement is often cold-pressed, unrefined, sometimes mixed with antioxidants or lignans, and stored refrigerated to prevent exactly the oxidation that painting depends on. It can dry, but unpredictably, and it yellows more than refined artist linseed. Artist-grade linseed oil (cold-pressed, refined, or alkali-refined) is inexpensive enough that the saving is negligible.
Hardware-store “boiled linseed oil” is a separate case: it contains metal driers and often petroleum solvents, dries very fast, darkens heavily, and is formulated for wood finishing. It is not suitable for fine art.
Why artist oils cost more than kitchen oils
Processing explains most of the price difference. Artist linseed oil is pressed, then refined to remove mucilage, free fatty acids, and color bodies; some grades are sun-bleached or heat-polymerized (stand oil). Those steps control drying speed, yellowing, clarity, and film strength. Cooking oil is refined for flavor, smoke point, and shelf life, and often has antioxidants added. The two products come from the same seeds and then diverge completely.
The one good use for cooking oil in a studio
Cooking oil is an excellent brush cleaner for oil paint. Because wet oil paint dissolves in oil, a cheap vegetable oil lifts pigment from bristles without solvent fumes.
- Wipe excess paint from the brush on a rag.
- Pour a little vegetable, canola, or baby oil into a shallow dish.
- Work the brush in the oil, pressing gently, then wipe on the rag. Repeat until the rag stays clean.
- Wash with brush soap or dish soap and lukewarm water to remove the oil completely.
- Rinse, reshape, and dry flat.
The soap step matters. Oil left in the bristles will go rancid and stiffen them. Cooking oil also removes oil paint from skin more gently than solvents; follow with soap.
Used oil from this process should be disposed of with pigment sludge, not poured down the drain.
Inexpensive, correct alternatives
If the appeal of cooking oil is cost or availability, these options solve the same problem properly:
- Artist-grade refined linseed oil. A small bottle lasts months and costs little more than a bottle of good olive oil.
- Artist safflower or walnut oil. Slower drying and less yellowing, for whites and pale colors.
- Stand oil. Thickened linseed oil for glazes and leveling.
- Odorless mineral spirits. For thinning lean early layers (not an oil, but the companion to one).
- Solvent-free painting. Use the paint straight from the tube with a touch of linseed oil; many painters never thin further.
- Water-mixable oils. Thin and clean with water; no solvent or extra oil required.
How to check whether any oil will dry
If you are curious about a bottle that is not on the lists above, a simple thin-film test shows how it behaves without risking a painting. Brush a very thin layer of the oil onto a scrap of glazed tile, glass, or primed board and set it somewhere dust-free at room temperature. Check it at one day, one week, and one month.
- Dries to a firm, non-tacky skin: a true drying oil. It may still need refining before it is suited to fine art, but the chemistry works.
- Stays tacky or gummy: semi-drying at best. Fine for experiments, a poor choice for work you want to keep.
- Stays wet, soaks into the board, or leaves a greasy ring: non-drying. It will never cure in a paint film.
Keep the sample thin. A thick puddle of any oil can wrinkle on top while staying liquid underneath, which tells you nothing useful about how it would behave mixed into paint.
What to do if you already used cooking oil in a painting
It happens, usually to someone who ran out of medium mid-session. The right response depends on how much oil went in and how long ago.
- Caught while wet: scrape the affected paint off the surface with a palette knife and blot the area with a lint-free rag. Mineral spirits on a rag will lift most of the remaining oil from a non-absorbent ground.
- Dry to the touch but still soft or greasy: do not varnish or paint over it. Give the piece several more weeks, then test a hidden corner with a fingernail. A film that dents easily has not cured.
- Oil has beaded or left a halo: the affected passage usually has to be removed and repainted. Sanding or scraping back to the ground and starting that area again is more reliable than trying to seal the problem in.
- Only a trace was used: when the oil was a few drops stirred into a large amount of tube paint, the surrounding linseed will often carry the film. Keep that layer thin, let it dry fully, and watch it for signs of softness before adding further layers.
Whichever case applies, keep the painting flat and out of the sun while it is in question, because a soft surface collects dust and picks up marks quickly.
Common misconceptions
“Oil is oil.” Chemically, drying and non-drying oils are different in the exact property that makes paint harden.
“The old masters used whatever they had.” They used linseed, walnut, and poppy, which were understood as drying oils even then. Olive oil was abundant in Renaissance Italy and was not used as a paint binder.
“It dried for me.” The linseed oil already in the tube paint will dry around the added cooking oil, giving a skin that feels dry while the layer beneath stays soft. The problems show up months later.
“Walnut oil from the store is the same as artist walnut oil.” Close in chemistry, different in refinement, additives, and shelf life.
FAQs
Can you use vegetable oil to thin oil paint?
No. Generic vegetable oil (usually soybean, canola, or a blend) is semi-drying or non-drying. Paint thinned with it stays soft, attracts dust, yellows, and can go rancid.
Can you use olive oil for oil painting?
No. Olive oil is a non-drying oil and will never harden. It is one of the worst choices because it stays liquid indefinitely and beads on the surface.
Can you use sunflower oil for oil painting?
Not reliably. Traditional high-linoleic sunflower oil is semi-drying and cures slowly and weakly; the high-oleic sunflower oil in most supermarket bottles is effectively non-drying. Use artist-grade safflower or linseed instead.
Is grocery store walnut oil okay for oil painting?
It is a true drying oil and the best of the kitchen options, but it may contain antioxidants that slow curing and impurities that affect long-term clarity. Artist-grade walnut oil is the dependable version.
What household oil can clean oil paint brushes?
Any cheap cooking oil or baby oil lifts wet oil paint from brushes. Work the brush in oil, wipe, then wash thoroughly with soap and water so no oil remains in the bristles.
Why does oil paint dry if oil does not evaporate?
Drying oils harden by oxidation: oxygen bonds to the oil’s fatty acids and links them into a solid network. Non-drying cooking oils lack enough reactive bonds for this to happen.
Final Thoughts
Cooking oil fails as a painting medium for a simple chemical reason: it does not cure. Linseed, walnut, poppy, and artist-grade safflower do, which is why they are the oils in the paint to begin with. Keep the kitchen oil for cleaning brushes, where it is wiped away, and buy a small bottle of refined linseed oil for the painting itself.
How oils cure, and how long that takes, is one of the defining traits of the medium and a major factor in deciding whether oil or acrylic suits you. The detailed breakdown of how oil and acrylic paints differ covers drying, handling, surfaces, and cleanup side by side.
