Oil painting mediums explained: what they do and when to use them
Oil painting mediums are one of the aspects of the medium that confuses beginners most. The paint comes out of the tube ready to use — so what are mediums actually for, and do you really need them?
The short answer is that you can paint perfectly well with oil paint straight from the tube, thinned occasionally with a little solvent, and many painters do exactly that. But mediums open up a significant range of additional possibilities — controlling drying time, adjusting consistency, achieving specific surface qualities, and making certain techniques considerably easier. Understanding what the main mediums do and when to use them makes the whole practice of oil painting more deliberate and more controllable.
This guide covers the most important oil painting mediums, explains what each one does in practical terms, and gives clear guidance on when to use them. It is written for beginners and for painters who have been working with oils for a while but have never quite got to grips with this aspect of the medium.
First: the difference between solvents and mediums
These two things are often confused, so it is worth being clear from the start.
Solvents — turpentine, mineral spirit, Zest-It — are used to thin paint to a more fluid consistency and to clean brushes and equipment. They evaporate completely as the paint dries, leaving no residue in the paint film. Solvents make paint leaner (lower oil content) and faster drying. Used alone as a thinner, in small amounts, they are perfectly acceptable — particularly for early, lean layers. Used in excess, or in later layers over richer paint, they can weaken the paint film and cause problems over time.
Mediums are added to paint to modify its handling properties in ways that go beyond simple thinning. They typically contain oil, resin, or a combination of both. Unlike solvents, mediums remain in the paint film when dry and become part of the permanent paint layer. They affect how the paint flows, how it dries, how it looks when dry, and how it behaves on the brush. The right medium for a given situation depends entirely on what you want the paint to do.
Linseed oil
Linseed oil is the most traditional and widely used oil painting medium, and the one that most artists encounter first. It is the same oil used as the binder in most oil paints — adding more of it simply increases the oil content of the paint.
What it does: it increases flow and transparency, slows drying time, and produces a slightly glossier finish. A small amount added to stiff paint from the tube makes it more fluid and easier to brush out smoothly. It improves the adhesion of each layer to the one beneath and increases the flexibility of the dried paint film.
Cold-pressed linseed oil — the type used by Wallace Seymour in their oil paints — is the highest quality variety: lighter in colour, more free-flowing, and considered to produce a more stable dried film than heat-processed alternatives. Refined linseed oil is the standard type most widely available and works well for most purposes.
The main caution with linseed oil is that it yellows slightly over time, particularly in dark conditions. This is rarely a problem in practice for most colours, but it is worth bearing in mind for very light or white areas — stand oil or a non-yellowing medium is preferable there.
When to use it: when you want to increase the fluidity and transparency of paint, slow drying time, or enrich the surface quality of later layers. Add only small amounts — a little goes a long way, and too much oil in a paint layer risks wrinkling and long-term instability.
Stand oil
Stand oil is linseed oil that has been heated and thickened to a honey-like consistency. It behaves quite differently from raw linseed oil despite coming from the same source.
What it does: it increases flow and levelling — paint mixed with stand oil tends to self-level as it dries, reducing visible brushmarks and producing a very smooth, enamel-like surface. It dries to a tougher, more flexible film than raw linseed oil and yellows less. It also dries somewhat faster than raw linseed.
Because of its thick consistency, stand oil is usually diluted with a little solvent before adding to paint. It is particularly useful for glazing — thin, transparent layers of colour applied over dried paint — where its self-levelling quality produces an exceptionally smooth, even glaze.
When to use it: for glazing, for achieving a very smooth painted surface, and in final layers where you want maximum durability and minimum yellowing.
Alkyd mediums
Alkyd mediums are synthetic resin mediums that dramatically speed up the drying time of oil paint. The most widely known is Liquin, made by Winsor & Newton, but various versions are available from different manufacturers.
What they do: an alkyd medium added to oil paint typically reduces drying time from days to hours — a thin layer can be touch-dry overnight rather than in two or three days. They also increase the transparency and flow of the paint, making them useful for glazing as well as general painting. The dried film is tough and flexible.
For beginners in particular, alkyd mediums can be transformative. The slow drying of oil paint is one of the main frustrations for people starting out, and being able to work over a previous layer the next day rather than waiting several days makes the painting process feel considerably more manageable.
The trade-off is that alkyd mediums reduce the working time of the paint — it starts to set up more quickly on the palette and on the canvas. This is rarely a problem in practice but is worth being aware of.
When to use it: whenever faster drying is useful — which for most beginners is most of the time. Particularly good for underpainting, for building up layers quickly, and for glazing over dried passages.
Wallace Seymour Fast Drying Oil Glaze Medium
This is the medium we most commonly recommend alongside Wallace Seymour oil paints at Craft and Canvas, and for good reason. Because Wallace Seymour oils are made without added driers, drying times naturally vary across the palette — earth colours and cadmiums dry relatively quickly while blacks and some blues dry more slowly. The Fast Drying Oil Glaze Medium, added at 10 to 20%, brings drying times into balance across the palette and adds a beautiful depth and translucency to the paint.
It works particularly well for glazing — thin, luminous layers of colour that allow the paint beneath to show through — and for painters who want the quality of Wallace Seymour oils with more predictable drying times than the unaided paint provides.
When to use it: with Wallace Seymour oils throughout the painting process, and specifically when glazing, when balancing drying times across the palette, or when you want to increase the translucency and depth of a colour.
Retarder mediums
Retarder mediums do the opposite of alkyds — they slow down the drying time of oil paint further. Given that oil paint already dries slowly, beginners sometimes wonder who would ever want this.
The answer is painters working on large canvases, or using techniques like wet-into-wet blending across wide areas, where they need extended working time to keep the entire painting surface workable simultaneously. Retarder can also be useful in hot, dry conditions where paint dries faster than usual.
When to use it: large-scale wet-into-wet work, complex blending passages, or any situation where you need more working time than straight oil paint provides.
Impasto mediums
Impasto mediums are thick gels added to oil paint to increase its volume and body without diluting the colour. They allow paint to be built up into heavy, sculptural textures — raised brushmarks, palette knife passages, thick gestural marks — that retain their three-dimensional quality as they dry.
Oil paint from the tube, particularly a high-pigment paint like Wallace Seymour, already has enough body to hold some impasto without medium. Adding an impasto gel extends this capacity significantly, allowing much heavier applications without the risk of the paint cracking or sagging as it dries.
When to use it: for texture work, expressive palette knife painting, and any technique where physical surface quality is part of the intention.
Varnish
Varnish is not strictly a medium — it is applied to the finished, fully cured painting rather than mixed with the paint. But it is worth including here because it is a final step that beginners often overlook and that makes a significant difference to both the appearance and the longevity of finished oil paintings.
Varnish protects the paint surface from dust, atmospheric pollutants, and physical damage, and it unifies the surface sheen of the painting — areas of the paint film that have dried matt alongside areas that are glossy can make a painting look patchy and unfinished, and a coat of varnish resolves this immediately.
A removable, non-yellowing varnish is strongly recommended. This can be taken off and replaced if the painting is cleaned in the future, without disturbing the paint film beneath. Apply varnish only when the painting is fully cured — typically six months to a year after completion for a thickly painted work.
When to use it: on fully cured finished paintings, as a protective and finishing layer.
Frequently asked questions about oil painting mediums
Do I need to use a medium at all? No — oil paint can be used straight from the tube, thinned only with a little solvent if needed. Many painters work this way, particularly in the early stages of learning. Mediums become useful as your practice develops and you want more control over specific properties of the paint. Starting without mediums and introducing them one at a time as you identify a specific need is a perfectly sensible approach.
Can I mix different mediums together? Some combinations work well — stand oil diluted with a little solvent, for instance, is a classic glazing medium. But mixing an alkyd medium with a slow-drying oil works against itself and produces unpredictable results. As a general rule, stick to one medium type at a time until you understand what each one does on its own.
How much medium should I add to paint? Less than you think. A small amount of medium — typically 10 to 20% of the paint volume — is sufficient to change its handling properties noticeably. Adding too much medium weakens the paint film and can cause problems with drying and long-term stability.
What is the best medium for a complete beginner? An alkyd medium such as Wallace Seymour Fast Drying Oil Glaze Medium, or Liquin, is the most immediately useful for most beginners because it solves the most common frustration — slow drying — while also improving the flow and transparency of the paint. A small bottle alongside your paints from the start is a very practical choice.
Can I use linseed oil from the kitchen? No. Food-grade linseed oil (also sold as flaxseed oil) is not the same product as artist's linseed oil. It is processed differently and will not dry correctly in a paint film. Always use artist-grade linseed oil specifically formulated for oil painting.
What happens if I use too much medium? Too much medium — particularly oil — can cause the paint film to wrinkle as it dries, to remain permanently tacky, or to crack over time. It can also cause paint to run and pool rather than staying where it is applied. The fat over lean principle (each successive layer should be at least as oil-rich as the one beneath) provides a framework for managing medium use across the layers of a painting.
Shop oil painting mediums at Craft and Canvas
We stock Wallace Seymour oil painting mediums — including the Fast Drying Oil Glaze Medium — alongside the full Wallace Seymour oil colour range at Craft and Canvas in Hebden Bridge and online at craftandcanvas.co.uk.
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