The brush is the most expressive instrument for ink drawing. It is erroneous to imagine that it cannot produce very fine lines; with the best brushes, both broad and hair-thin lines can be drawn, smoother and finer, perhaps, than with the finest nib.
The best brushes are of squirrel, ichneumon, or red sable (kolinsky) hair. They are round and must run to a needle point when wet. It is a professional touch when buying brushes to ask for water to test the point. It may look even more professional to lick the hairs to see if they form a firm point, but it is not very dainty and is no more effective. It is not enough simply to rely on well-known trade names when buying brushes; even with the best of intentions brushes cannot be identical. A further indication of quality besides price and name is that the best brushes always have seamless ferrules.
The brush size is measured in numbers, beginning at 0 and going up to about 20 or more. It is valuable to train oneself from the first to work with the thickest possible brushes. One works more quickly and with more expressiveness, and with the best quality, thick brushes it is perfectly possible to make fine lines. Thick brushes hold a great quantity of color, so there is no need to dip so frequently into the paint as with a fine brush. One can draw with fine strokes for much longer without the brush drying. Thin brushes under No.6 are really suitable only for closely detailed work and corrections.
You will soon learn to judge and value a good brush if you try working with a poor one! There are some of badger and cow hair which are far from poor, but - you must ty for yourself and see the difference! Most brushes imported from China are of wolf's hair. They are certainly no better than sable hair brushes but perhaps more resistant. India ink and its soap solvent affects them all severely, and they soon become brittle. Perpetual rinsing is tiresome when one is at work and it does not help much. The caustic attacks the hairs as soon as they are wet. Rinsing in vinegar and water after use is helpful, as it neutralizes the alkali.
Genuine Chinese ink does not damage the brush, apart from the gradual mechanical wear inevitable for any brush. If it is not essential that the drawing be waterproof, black watercolor can also be used. It is much more pleasant to work with and a more expressive medium than India ink, and it does not damage the brushes.
There is a paint based on casein which is waterproof. It can be thinned with water, but once dry, it is not water-soluble. Casein is one of the nonreversible glues. Glues are called reversible if they can be dissolved again after they have set. Casein is soluble only in a caustic, however, and this damages the brushes. These waterproof colors are best used opaque, without making them transparent by thinning. They have a compact consistency which can be very attractive. Their black pigment is a fine soot.