Bristle Brushes.—The sable brush or pencil is often necessary; but oil painting is practically always done with the bristle, or "hog hair," brush. These are the ones which will make up the variety of kinds in your six dozen. A good bristle brush is not to be bought merely by taking the first which comes to hand. Good brushes have very definite qualities, and you should have no trouble in picking them out. Nevertheless, you will take the trouble to select them, if you care to have any satisfaction in using them.
The Bristle.—You want your brush to be made of the hair just as it grew on the hog. All hair, in its natural state, has what is called the "flag." That is the fine, smooth taper towards the natural end of it, and generally the division into two parts. This gives the bristle, no matter how thick it may be, a silky fineness towards the end; and when this part only of the bristle is used in the brush, you will have all the firmness and elasticity of the bristle, and also a delicacy and smoothness and softness quite equal to a sable. But this, in the short hair of an artist's brush, wastes all the rest of the length of the hair; for it is only by cutting off the "flag," and using that, which is only an inch or so long, that you can make the brush. Yet the bristle may be several inches long, and all this is sacrificed for that little inch of "flag." Naturally the "flag" is expensive, and naturally also the manufacturer uses the rest of the hair for inferior brushes. These latter you should avoid. These inferior brushes are made from the part of the bristle remaining, by sandpapering, or otherwise making the ends fine again after they are cut off. But it is impossible to make a brush which has the right quality in this way.
Selection.—Never buy a brush without testing its evenness, as has been advised in the care of sables. Feel carefully the end of the bristles also, and see that the "flag" is there. All brushes are kept together for packing by paste in the bristles. See that this is soaked off before you test your brush.
Round or Flat.—It will make little difference whether you use round or flat brushes. The flat brush is most commonly preferred now, and most brushes are made that way. So you had better get that kind, unless you have some special reason for preferring the round ones.
Handles.—Whether the handles are nicely polished, also, is of no importance. What you are to look to is the quality of the bristles and of the making; the best brushes are likely to be nicely finished all over. But if you do find a really good brush which is cheaper because of the plain handle, and you wish to save money, do it by buying the plain-handled one.
Sizes and Shapes.—You will need some quite large brushes and some smaller ones, some square ones and some pointed.
[Here] are three round brushes which, for all sorts of painting, will be of very general utility. For most of your brushes select the long and thin, rather than the short and thick ones. The stubby brush is a useless sort of thing for most work. There are men who use them and like them, but most painters prefer the more flexible and springy brush, if it is not weak. So, too, the brush should not be too thick. A thick brush takes up too much paint into itself, and does not change its tint so readily. For rubbing over large surfaces where a good deal of the same color is thickly spread on the canvas, the thick, strong brush is a very proper tool. But where there is to be any delicacy of tone, it is too clumsy; you want a more delicate instrument. The same proportions hold with large and small brushes, so these remarks apply to all.