The first step in cleaning a paintbrush used for oil-based paint is to prepare a fully ventilated workspace before you touch any solvent. Open nearby windows, turn on a ventilation fan, and make sure there are no open flames, lit cigarettes, or high-heat sources anywhere near your work area. Many common solvents for oil-based paint release strong, volatile fumes that can cause dizziness if inhaled in large amounts, and they carry a significant fire risk if exposed to high temperatures. You should also put on a pair of durable protective gloves to keep solvent off your skin, and wear basic eye protection to avoid accidental splashes while you work.
Before you introduce any solvent, take a moment to remove as much excess oil-based paint from the brush as possible. Press the bristles gently against the inner edge of your original paint can, and wipe the brush back and forth on a clean piece of scrap cardboard or old newspaper. This simple step removes the thickest, most concentrated paint residue right away, so you do not waste large amounts of solvent on material that could have been scraped off easily. It also makes the rest of the cleaning process far faster, and reduces the amount of paint you end up introducing into your cleaning solvent.
Initial Solvent Rinse for Caked-On Residue
Pour a small amount of your chosen solvent into a clean, wide-mouthed container that gives the brush plenty of room to move. You only need enough liquid to submerge the bristle portion of the brush, not the entire handle or ferrule. Dip the brush into the solvent, and work the bristles gently against the bottom and sides of the container in slow, circular motions. This motion pushes the solvent deep between the bristles, and dissolves the thick layers of oil-based paint that are trapped near the base of the brush.
Do not scrub the brush hard against the bottom of the container, because this can bend and fray the bristles permanently, ruining the fine, even edge you rely on for clean painting work. Instead, squeeze the bristles gently between your thumb and forefinger as you pull the brush out of the solvent, working the dissolved paint out from the core of the bristle cluster. Repeat this process a few times, and replace the solvent with a fresh batch once the liquid turns thick, cloudy, and dark with dissolved paint.
Deep Cleaning for Trapped Residue Near the Ferrule
Even after several rinses, small traces of oil-based paint often get trapped right at the base of the bristles, where they meet the metal ferrule. If you leave this residue in place, it will harden over time, make bristles stiff and uneven, and eventually cause the brush to lose its shape completely. To reach this hidden area, dip the tip of a soft, lint-free cloth into a small amount of clean solvent, and wrap it around the base of the bristle cluster. Wipe gently in a twisting motion to dissolve and lift out the trapped paint that the initial rinse could not reach.
For brushes that have dried slightly with oil-based paint still left in the bristles, you can let the brush soak in a shallow bath of solvent for a short period of time. Make sure you only submerge the bristle portion, and never let solvent sit high enough to seep under the ferrule for hours on end. Leaving the brush sitting too deep in solvent for too long can dissolve hidden adhesives that hold the bristles in place, and cause whole clumps of bristles to fall out the next time you use the brush. Check the brush every few minutes during soaking, and work the bristles gently with your fingers once the hardened paint starts to soften and break apart.
Final Rinse and Post-Cleaning Care
Once no more colored paint residue is coming out of the bristles, you can move on to the final rinse step. Wash the brush gently with a mild, soap-based solution and warm water, working the soap through the bristles with your fingers to remove every last trace of leftover solvent and dissolved paint. Keep rinsing under running warm water until the water runs completely clear and free of any cloudiness or color. This step removes all remaining solvent residue, so it does not stay trapped in the bristles and affect the finish of your next painting project.
After rinsing, shake out any excess water gently, and reshape the bristles back to their original, flat or pointed form with your fingers. Hang the brush upside down in a well-ventilated area, so any remaining water or small traces of residual liquid drip out of the bristles, instead of seeping back up into the ferrule. Let the brush dry completely in this position before you store it away, and this will keep the bristles soft, straight, and ready for your next oil-based paint project. Properly cleaned and cared for this way, a good brush will hold its shape and deliver smooth, even coats for a very long time.