A dark boundary has formed at the bottom of an even colour fill. What is the most suitable way to prevent it?

Correct answer: Lift the excess pooled paint with a clean damp brush

The governing concept is controlled paint flow in an even wash. As liquid colour moves downward, it can collect at the lower edge; the extra pigment then dries as a dark boundary. Option D is correct because a clean, damp brush can lift the pooled excess before drying. Adding paint or pausing the brush increases pooling, while a flat sheet alone does not remove accumulated colour.