Watching Paint Dry: Understanding the drying times for oil paint
Traditional oil paints are bound with drying oils. This is what gives them their unique working properties and makes them much slower drying than water-based media.
A drying oil is a vegetable oil which dries by oxidation (explanation below) and there are many types including poppy seed oil and safflower oil among others. Linseed oil is the one used in the majority of oil paints because it dries to the most durable film.
What effects do drying times have on oil paintings?
The main effects are dependent on how you layer your paints. If done incorrectly, you could create damage to your artwork. For example when underpainting, if a faster-drying layer is applied over the top of oil underpainting, this will be pulled apart as the slower-drying colour contracts. This is also true of colours which only surface dry such as cobalt. For underpainting, we would recommend an underpainting white, alkyd white or flake white (in linseed oil) because of their quick and thorough drying time.
In addition, paintings made in layers are also less likely to crack if the underpainting is thickly applied – that is, a thin paint film, not an excessively thinned paint film. It then has more time to dry thoroughly.
Which colours dry faster?
Most brands of oil paints contain driers in some colours in order to bring the drying times closer to range between 2 and 10 days. This helps to prevent problems with slow-drying colours and is perfectly safe for the paint film when controlled by experienced chemists.
Fortunately the drying rates of colours are rarely a problem because colours are almost always mixed on the palette and so the drying times tend to equalize to a great degree.
However, the following list gives a guide to the drying rates of pigments in linseed oil. Please remember that all colours made with poppy oil or similar will dry relatively slower than in the list
• Cobalt blues
• Flake white
• Manganese blue and violet
• Siennas and Umbers
• Chromium oxide green
• Cobalt greens and violet
• Mars colours
• Phthalyocyanine blue and green
• Some natural iron oxides
• Ultramarine blues and violet
• Arylamide yellows
• Alizarin crimson
• Green earth
• Ivory black
• Lamp black
• Rose madder
• Some natural iron oxides
• Titanium white
• Vandyke brown
• Yellow ochre
• Zinc oxide
Using Winsor & Newton Oil Colours
Both Artist's Oil Colour and Winton Oil Colour are combined with Linseed oil and will behave in the way described above. In addition to this, it is worth stressing that, as Artisan Water Mixable Oil Colour is also Linseed and Safflower based (not water based) it too has exactly the same drying mechanism and therefore rate of drying.
Speeding the drying rate
The safest way to accelerate the drying rate of oil colours is to use Liquin, which speeds the drying by about 50%. Thickened linseed oil can also be used and will speed drying by about 10%.
Neat driers (such as cobalt) are not recommended because they can crack the paint. The safe addition of driers depends on each pigment and is best left to the experience of manufacturers.
The Winsor & Newton Liquin range of alkyd mediums, offer the ability to combine an alkyd resin with traditional oil colour effectively halving the drying time of the colour from the tube and result in an increased resistance to yellowing.
In particular, all the Liquin mediums will halve the drying time of oil colours from 2- 12 days to 1-6 days.
Winsor & Newton in fact used alkyds at the beginning of the 1950's in craft colours, outdoor colours, varnishes and primers. In contrast to the more traditional natural resins of dammar, copal or mastic, that were the basis of the majority of the mediums on offer at the time the alkyd mediums ability to halve the drying times of oil colours, was a characteristic not seen with other traditional painting media.
This new ability to progress a painting more quickly had a profound effect on studio practice and Liquin shortly became what it is today - the most popular and commonly used oil painting medium.
The ingredients of Liquin are complex chemicals that are far more stable than the natural resin mediums of the past. Our chemists combine their cumulative experience of traditional mediums with modern paint technology and there is no doubt about the working characteristics and stability of Liquin.
The other most common question refers to the oil painting rule - ‘fat over lean'. Liquin is usually used instead of oil as a medium. Therefore, there is no need to add oil to increase flexibility in successive layers. When painting in layers simply increase the proportion of medium by adding more Liquin or reducing the solvent used as you progress.
The Liquin range - a comprehensive family of mediums
The Liquin range offers a comprehensive and varied selection to the artist, all of which are reinforced by the reliability and durability synonymous with the Liquin name. All Liquin products are suitable for use with conventional oil colour (Artists Oil Colour & Winton Oil Colour) whilst Griffin Fast Drying Oil Colour and Artists' Oilbar and are intermixable.
The family includes:
Liquin Original – our most popular liquid alkyd medium
Liquin Fine Detail – for detailed brushwork
Liquin Light Gel – a slight gel that breaks down on brushing for a non-drip effect with colour
Liquin Impasto – a semi-gloss impasto medium that retains crisp textures and brush strokes
Griffin Alkyd Fast Drying Oil Colour
Another way to shorten the drying rate of your oil painting is to use Griffin Fast Drying Oil Colour. The Griffin range is formulated using an oil modified alkyd resin as the binder as apposed to a traditional drying oil.
Alkyds are polyesters modified by adding fatty acids. They are derived from polyols and a dicarboxylic acid or carboxylic acid anhydride. The name alkyd is in turn derived from these components - alcohol and acid or anhydride. They were introduced in 1928 by Kieule and had been used in lacquers and wood finishes.
Griffin Fast Drying Oil Colour offers a full palette of 50 colours enabling the traditional oil techniques of both impasto and glazing in considerably less time and a painting can be completed in a single session. The range was first launched in 1976 with its iconic labels, a set of which are held in the Winsor & Newton Museum.
Artisan Water Mixable Oil Colour & Fast Drying Medium
Artisan Water Mixable Oil colour differs from traditional oil colour in that it is possible to thin the colour and clean it up with water. Its benefits also include the fact that it can be used without the need for hazardous solvents, making it a more environmentally friendly option for artists who share work space, or who are painting at schools or at home.
In order to control drying times, it contains within its range of specially formulated oils, thinners, mediums and varnishes - a Fast Drying Medium. This not only improves the flow of painting but speeds up drying time by about 50%, allowing further layers to be applied more quickly.
Retarding the Drying Rate of Oil Painting
Sometimes it is also necessary for artists to retard the drying rate. To achieve this use a 50:50 stand oil and turpentine mixture to thin it.
The Oxidation Process (drying process) explained
Oil colours, unlike water based colours which dry by evaporation, dry as the result of an oxidative reaction, an oxidative reaction being the absorption of oxygen from the air. This reaction is a complex one that can be broken down into different stages; The Autoxidation phase, the Polymerisation phase and finally the Stationary phase.
Vegetable oils (such as linseed oil and safflower oil) are made up of a mixture of various triglycerides that differ in terms of their fatty acid constituents. A triglyceride is a glyceride in which the glycerol is esterified with three fatty acids. Structurally this means that these oils contain long chains of hydrocarbons.
As oxygen is absorbed during the drying process, it attacks these hydrocarbon chains and produces free radicals.
These free radicals are highly reactive substances due to the presence of an unpaired electron. As more and more reactions occur, further free radicals are produced which start to polymerise and the process terminates when they form a new bond as their unpaired electrons combine.
This polymerisation stage takes days and weeks to complete after which the paint film will feel dry to the touch. However chemical changes in the paint film continue.
During this final stage the polymer chains begin to cross link. Covalent bonds formed by adjacent molecules result in a molecular network throughout the oil colour. This results in a stable and dry paint film.
| Structure of a triglyceride found in linseed oil
It is these three stages that give the relatively long drying time for oil colours.
Understanding the drying rates of oil colours and the impacts of oils and mediums is essential for every oil painter if they are to create stable art works that will stand the test of time. By experimenting with the different mediums and getting to know your oil colours there is no doubt that you are on your way to mastering the techniques of this classical art form.