This section is from the "Henley's Twentieth Century Formulas Recipes Processes" encyclopedia, by Norman W. Henley and others.
Varnish brushes, and brushes used in varnish stain, buggy paint, and all color in varnish require different handling than paint brushes. They should be more thoroughly dry cleaned, in order that all loose hairs may be worked out. After working them through the hand it is a good thing to pass the brush back and forth over a sheet of sandpaper. This rough surface will pull out the loose bristles and smooth down the rough ends of the chisel point. The brush should then be washed by working it for a few minutes in clean turpentine and swinging it dry. It should never be put in water. For carriage work and fine varnishing the brush should be broken in on the rubbing coat in order to work out all the dust particles before it is used on the finishing coats.
For the first 2 or 3 days new brushes require special care while at rest. They should be dipped in raw oil or the paint itself and smoothed out carefully, then laid on their sides over night. The chisel-pointed brushes should be set at an incline, the handle supported just enough to allow the brush to lie along the point. This is done to prevent twisting of the bristles, and to keep the shape of the brush. It is necessary to do this only 2 or 3 times before the shape becomes set.
An important principle in brush care is never to leave the brush on end while at rest. Even for temporary rest during a job the brush should never stand on end. At night it should always be placed in a "brush-keeper"—a water-tight box, or a paint keg, with nails driven through the sides on which the brushes can be suspended in water. Holes are bored in the handles so the brush will hang free of the bottom, but with the bristles entirely under water. Before placing
them in water the brushes should be wiped so as not to be too full of paint, but not cleaned.
Varnish brushes should be kept at rest in turpentine and varnish, or better, in some of the varnish that the brush is used for. They should preferably not be kept in turpentine, as that makes the brush " lousy"—roughening the bristles.