A brush consists of three parts: the tuft, the ferrule and the handle.
- The tuft is a bundle of animal hairs or synthetic fibres tied tightly together at the base;
- The ferrule is a metal sleeve that surrounds the tuft, gives the tuft its cross sectional shape, provides mechanical support under pressure, and protects from water wearing down the glue joint between the trimmed, flat base of the tuft and the handle;
- The lacquered wood handle, which is typically shorter in a watercolour brush than in an oil painting brush, has a distinct shape—widest just behind the ferrule and tapering to the tip.
When painting, painters typically hold the brush just behind the ferrule for the smoothest brushstrokes.
Hairs and Fibres
Brushes hold paint (the “bead”) through the capillary action of the small spaces between the tuft hairs or fibres; paint is released through the contact between the wet paint and the dry paper and the mechanical flexing of the tuft, which opens the spaces between the tuft hairs, relaxing the capillary restraint on the liquid. Because thinned watercolour paint is far less viscous than oil or acrylic paints, the brushes preferred by watercolour painters have a softer and denser tuft. This is customarily achieved by using natural hair harvested from farm raised or trapped animals, in particular sable, squirrel or mongoose. Less expensive brushes, or brushes designed for coarser work, may use horsehair or bristles from pig or ox snouts and ears.
However, as with paints, modern chemistry has developed many synthetic and shaped fibers that rival the stiffness of bristle and mimic the spring and softness of natural hair. Until fairly recently, nylon brushes could not hold a reservoir of water at all so they were extremely inferior to brushes made from natural hair. In recent years, improvements in the holding and pointing properties of synthetic filaments have gained them much greater acceptance among watercolourists.
There is no market regulation on the labelling applied to artists’ brushes, but most watercolourists prize brushes from kolinsky (Russian or Chinese) sable. The best of these hairs have a characteristic reddish brown colour, darker near the base, and a tapering shaft that is pointed at the tip but widest about halfway toward the root. Squirrel hair is quite thin, straight and typically dark, and makes tufts with a very high liquid capacity; mongoose has a characteristic salt and pepper colouring. Bristle brushes are stiffer and lighter coloured. “Camel” is sometimes used to describe hairs from several sources (none of them a camel).
In general, natural hair brushes have superior snap and pointing, a higher capacity (hold a larger bead, produce a longer continuous stroke, and wick up more paint when moist) and a more delicate release. Synthetic brushes tend to dump too much of the paint bead at the beginning of the brush stroke and leave a larger puddle of paint when the brush is lifted from the paper, and they cannot compete with the pointing of natural sable brushes and are much less durable. On the other hand, they are typically much cheaper than natural hair, and the best synthetic brushes are now very serviceable; they are also excellent for texturing, shaping, or lifting colour, and for the mechanical task of breaking up or rubbing paint to dissolve it in water.
A high quality sable brush has five key attributes: pointing (in a round, the tip of the tuft comes to a fine, precise point that does not splay or split; in a flat, the tuft forms a razor thin, perfectly straight edge); snap (or “spring”; the tuft flexes in direct response to the pressure applied to the paper, and promptly returns to its original shape); capacity (the tuft, for its size, holds a large bead of paint and does not release it as the brush is moved in the air); release (the amount of paint released is proportional to the pressure applied to the paper, and the paint flow can be precisely controlled by the pressure and speed of the stroke as the paint bead is depleted); and durability (a large, high quality brush may withstand decades of daily use).
Most natural hair brushes are sold with the tuft cosmetically shaped with starch or gum, so brushes are difficult to evaluate before purchasing, and durability is only evident after long use. The most common failings of natural hair brushes are that the tuft sheds hairs (although a little shedding is acceptable in a new brush), the ferrule becomes loosened, or the wood handle shrinks, warps, cracks or flakes off its lacquer coating.