Keeping brushes in good shape contributes significantly to good finishing results. Often cheap brushes are bought because one assumes that it won't be possible to clean a brush sufficiently well after use anyway. This is, however, a totally wrong assumption. The following instructions for cleaning are intended to give you long-lasting delight with more expensive, good-quality brushes; always carry out all steps of the cleaning process whenever a brush has been used and don't just leave a brush soaked in a solvent-filled container overnight, not even if you intend to continue painting the next day already. Follow these instructions and you will be rewarded with brushes that remain in perfect shape.
First remove any material left on the brush by squeezing it against the walls of the container. Then wash the bristles in a sufficient amount of thinner and, wearing protective gloves, massage them thoroughly with your hands. After this twirl the brush between the palms of your hands so that any solvent left is removed.
Don't worry about using too much solvent for washing the brush: it won't go off and you can use it again later. If you leave it to stand until the solid particles have settled to the bottom of the container, you can pour it through a coffee filter and get fairly clean solvent again for the next time you need some.
After the brush has been thus rough-cleaned, wash it properly in a mixture of plenty of warm water and a bit of hair shampoo by running your fingers through the bristles (commercials will tell you what shampoo to use!). Then wash out the solvent with running water. Repeat and rinse the bristles a second and a third time with fresh water.
Finally, carefully wrap the bristles in paper and put a rubber band or adhesive tape around it to hold the paper in place. This will ensure that the bristles remain straight while the brush is not used.Excerpt from my book Building Electric Guitars