A well-cleaned paintbrush will perform better, since clean bristles will spread finish more evenly. Residue can cause flagged bristle ends to clump, which will reduce their ability to distribute finish.
Nearly all finishes used to be petroleum-based, so brushes required mineral spirits for cleanup. But water-based finishes dominate the market now, and along with them comes the ability to clean up with water and soap, which means you can avoid harsh solvents.
1. Mix a liquid solution of 1 tsp laundry or dish detergent to 1 litre of water in an empty paint can. Swirl your used paintbrush in the can to dissolve residual finish on the brush.
2. Work the bristles with a rubber-gloved hand before rinsing them with clean water.
3. Put a lid on the can, and label it so you can reuse the detergent solution. When it’s no longer effective for cleaning, set the can outside with the lid off to let the water evaporate.
4. Gather up the residue with a shop spatula, and transfer it to a second labelled spent paint can. When you have a full can of residue, take it to your local hazardous waste depot to be disposed of properly.