When painting with acrylic paint, it is important to keep the brush clean. This means cleaning it regularly with a mild soap and water solution, and then rinsing it off completely. If the brush is not kept clean, the paint will start to build up on the bristles and create a film on the canvas. This can cause problems when painting, as the film can cause glare and reflections in your work. To avoid this, make sure to keep your brush clean by cleaning it regularly with a mild soap and water solution, and then rinsing it off completely.