How to Keep Brushes Clean

The best way in which to clean hair-brushes is with spirits of ammonia, as its effect is immediate. No rubbing is required, and cold water can be used just as successfully as warm. Take a tablespoonful of ammonia to a quart of water, dip the hair part of the brush without wetting the ivory, and in a moment the grease is removed; then rinse in cold water, shake well, and dry in the air, but not in the sun. Soda and soap soften the bristles and invariably turn the ivory yellow.

Source: The White House Cookbook, F.L. Gillette