Here’s a video on how to cut in a clean, sharp line when painting walls
Cutting in Top Tips
1. Use a Purdys 3" brush for ceilings and walls
2. Generously spread paint on to the surface an inch or so away form the ceilings edge
3. When brushing against the ceilings edge make your brush strokes as long as you can
4. Keep your eye on the line you want your brush to cut and your brush will follow
5. Practice makes perfect