What is an oil painting medium?
A medium is something you mix into oil paint to change how it behaves. Depending on the product, a medium can make paint flow more easily, change how glossy or transparent it is, thin it for early layers, or shorten or lengthen the drying time. Paint straight from the tube is often thick, so many painters use a medium at least some of the time. Others use none and rely on the oil already in the paint.
You do not need a medium to start. A small bottle of solvent and a bit of oil are enough for most early work. As you gain experience, you can try others and see what you like.
Solvents and thinners
Solvents thin paint by dissolving the oil binder, and they evaporate rather than becoming part of the paint film. They are used for early, lean layers and for cleaning brushes.
- Odorless mineral spirits: Widely used because they have a lower odor than some other options. Still use them with ventilation.
- Turpentine: A traditional solvent from pine resin. It has a strong odor and can irritate some people, so many painters prefer alternatives.
- Water-mixable oils: A separate type of paint designed to be thinned with water. They use different additives and should not be mixed carelessly with traditional oil mediums.
Solvents make a layer leaner, so they belong at the start of a painting. If you add too much solvent to later layers, the paint can become weak and underbound.
Drying oils
These oils become part of the paint film as they cure.
Linseed oil
Linseed oil, pressed from flax seeds, is the traditional oil binder in oil paint. Added to paint, it improves flow, can add gloss and transparency, and makes the layer fatter. It is a long-standing choice for glazing and for general painting. It can yellow somewhat over time, particularly in light colors and in dim conditions. Refined and cold-pressed versions exist and differ somewhat in color and handling.
Stand oil
Stand oil is linseed oil that has been heat-treated to a thicker, more viscous consistency. It is often described as giving a smooth, enamel-like flow with little brush texture, and it tends to yellow less than raw linseed oil in some accounts. It is usually diluted with solvent or mixed with other ingredients before use.
Other oils
Safflower and poppy seed oils are sometimes used in paints, especially for whites and pale colors, because they tend to yellow less. They are often described as slower or less robust drying than linseed oil. For painting mediums, linseed remains the usual reference point.
Alkyd mediums such as Liquin
Alkyd mediums are made with alkyd resin, a synthetic material. Liquin from Winsor and Newton is one familiar brand, and other makers offer similar products. Typical claims are that they speed up drying, improve flow, add some gloss, and help with glazing and fine detail. Paint mixed with an alkyd medium often becomes touch-dry in a shorter time than paint mixed with plain linseed oil, though the exact time varies by product, thickness and pigment.
Points to keep in mind:
- Read the manufacturer’s directions for the specific product, since formulations differ.
- Alkyd mediums can make paint feel stickier or more stringy for some painters.
- Because they speed drying, they can help with layered methods, but you should still respect fat over lean.
- Alkyd mediums can be used in the same painting as traditional oils, but ask the maker if you want to combine different products.
Should I use Liquin or linseed oil?
It depends on what you want.
- Choose linseed oil if you prefer a traditional approach, want a fat, glossy, workable layer, and do not mind slower drying.
- Choose an alkyd medium if you want faster drying, quick layering or smoother glazes.
- Choose neither if you like paint straight from the tube.
Many painters keep both and use them for different purposes.
Mediums and fat over lean
As covered in the oil painting method, each layer should generally have as much or more oil than the one below. A rough way to think about it:
- First layers: thinned with solvent only, or minimal medium.
- Middle layers: paint straight from the tube or with a small amount of medium.
- Final layers: more oil or medium for richer, fatter passages and glazes.
Avoid adding lots of solvent to upper layers over fat lower layers. If a medium mix contains a lot of fast-drying alkyd, treat it as a fat layer that dries faster, and follow the label guidance on layering.
Glazing and scumbling
A glaze is a thin, transparent layer of color laid over a dry layer, usually with a medium to increase transparency. A scumble is a thin, semi-opaque, often lighter layer dragged over a darker one. Both are used to alter color and soften transitions (acrylic painters glaze too; see painting layers with acrylic), for example in backgrounds. Transparent pigments work best for glazing, as explained in oil painting color theory.
How much medium to use
A common recommendation is to start with a small proportion, such as a few drops mixed into paint on the palette, and add as needed. Overdiluting weakens the paint film. Follow the label of your product and test on a scrap panel.
Varnishes are different
Varnish is a protective final coating, not a painting medium. Do not confuse the two. Waiting until the paint is dry enough is important, and manufacturers give guidance on when to varnish.
Safety and storage
- Work in a ventilated room.
- Keep solvent containers closed and away from heat.
- Rags with linseed oil or alkyd mediums can heat as they dry, so dispose of them safely in a sealed metal container or lay them flat to dry.
- Do not pour solvents down a drain. Follow local disposal rules.
Brushes and mediums
Medium use affects brush care, since oils and resins need to be cleaned out. See what type of brush to use for oil paint for brush types and care tips.
Frequently asked questions
What is an oil painting medium?
An additive that changes the consistency, gloss, transparency or drying time of oil paint.
What are the downsides of using oil-based paint?
Oil paint dries slowly, requires solvents and careful cleanup for traditional types, can yellow in some colors over time, and needs proper layering. Some painters see slow drying as an advantage, though.
Did Bob Ross use acrylic or oil?
He used oil paint, in a wet-on-wet approach, according to widely available descriptions of his television program.
What is oil painting?
It is painting with pigments bound in a drying oil, most commonly linseed oil, typically on a primed canvas, panel or other support.