How do you stop the dark Hogwarts colours from bleeding on the canvas?

Work in small sections and let each area dry before painting next to it, especially where dark colours sit beside lighter ones. Keep your brush rinsed and dried between colours, and use a light touch rather than loading the brush heavily.

Paint from the top of the canvas downwards where you can, so you are less likely to rest your hand on wet paint. A clean, dry cloth under your wrist also helps protect finished areas.