From Paul W. McCormack‘s “Mixing Color” article in a previous issue of The Artist’s Magazine:
To get the best painting results, keep your tools in good working order. For starters, that means taking the time to clean your brushes as you work. Keep some paper towels and a cup of turpentine or other solvent handy for this purpose. Simply wipe off thet bristles with a paper towel and dip the brush in the solvent, using a swirling motion to loosen remaining paint. Then remove the brush from the cup and wipe the bristles clean.