(five to eight days)
The speed at which oil paint dries depends on the colour. Some pigments act upon the drying oils in which they are bound, speeding up the drying process; others slow it down (see here). Earth pigments dry rapidly, acquiring a skin overnight, whereas alizarin crimson may need up to 10 days to become touch-dry.
To accommodate these extremes, some paint manufacturers add drying agents to the slower-drying pigments; others grind fast-drying pigments with slower-drying oils, to obtain a paint range with more consistent qualities. Others add no drying agents, allowing the artist to decide whether to use fast-drying mediums.
Tinting strength
There is a variation in the tinting strength of different pigments. For example, Prussian blue and alizarin crimson will produce vivid colours when added in even very small quantities to white, whereas terre verte and raw umber become very pale when mixed with only a little white. When mixing a pale tint using strong colour, always add it to the white and in very small quantities – otherwise, you may get through a great deal of paint for little result.
Differences
Manufacturers do not formulate their paints in the same ways, so although colours in different brands may have the same names, their contents vary not only in the appearance of the colour but also in their cost, consistency, handling qualities, permanence and drying rates.
Which white?
The most important pigment in the oil painter’s palette is white, because it is used more than any other colour. It is therefore essential to use good-quality whites; even if you are using student-quality paints, it is worth buying a large tube of artist-quality white, as it has better covering power than the student grade.
Several whites are available, each with different properties, although as a general rule titanium white is the most reliable and versatile (see here).
Whites ground in poppy or safflower oil should not be used for priming or extensive underpainting. They are slow-drying, and can cause cracking of subsequent paint layers unless allowed to dry thoroughly. Use flake white, which is quick and thorough-drying, or one of the alkyd or underpainting whites.
Alkyd paints
These are made from pigments bound in an oil-modified synthetic resin. They handle in the same way as traditional oil paints, but have the advantage of being much faster-drying – in normal use, the paint surface is generally dry within an hour. Alkyds may be mixed with oil paints, which has the effect of speeding up the oils’ drying time and retarding that of the alkyds, so that all the colours dry at a relatively even rate. Any supports that are suitable for oil and acrylic paints may be used for alkyds, once primed with oil or acrylic primer.
Water-friendly oil paints
A selection of alkyd and water-friendly oil paints
In recent years, a few manufacturers have produced ranges of oil paints in which the oil binder has been modified to mix with, rather than repel, water. This does not preclude the use of traditional oil-based mediums and diluents, but means that thinning paint and cleaning brushes can be done with water. The advantage is that this eliminates the use of solvents, to which many people are allergic, and avoids a possible build-up of potentially dangerous vapours.
Caring for your paints
Paints tend to solidify in the tube if left uncapped. Replace the cap once you have used the paint, and make sure the threads on the cap and neck remain clean. Stuck caps can be opened with pliers, or by holding the tube under hot running water. As a last measure, stand the tube upside down in turpentine or white spirit for a few minutes, so that the cap and top of the tube are covered. Always squeeze a tube of paint from the bottom upwards, thus ensuring that there is as little air as possible inside the tube.
Avoiding waste
Oil paints are expensive. A palette knife held at an oblique angle and scraped along a finished paint tube will help to remove the last scrap of paint.
Pigment strength
Prussian blue
Alizarin crimson
Terre verte
Raw umber
Note the contrast in tint between the two pigments on the left and those on the right, when they have all been mixed with the same amount of white.
Drying speeds of oil paint
The following is a guide to approximate drying speeds of pigments bound in linseed oil. The drying rates may vary between brands, and colours bound with safflower or poppy oil are relatively slow-drying. When colours are mixed together, their drying rates may be altered.
Flake white
Also known as lead white or silver white, this is a comparatively quick-drying, durable and flexible paint, widely used in underpainting. It accelerates the drying of colours mixed with it. Flake white lacks the opacity of titanium white and the whiteness of zinc white. It is harmful if it is swallowed, as it contains lead, so keep it out of the reach of children.
Titanium white
Also known as permanent white, this is the whitest and most opaque white, which dries very slowly to a soft, chalky film. Its strong covering power is useful for mixing tints, and for highlights and final painting. It is classed as non-hazardous.
Zinc white
This has a pure, cold white appearance which does not darken with time. It is semi-opaque, and is suitable for tinting and glazing, but not for underpainting. Zinc white dries very slowly to a hard, brittle film. It is classed as non-hazardous.
SEE
