After several layers of negative painting the composition has become too dark and heavy. What may be the main cause?

Correct answer: Excessively dark paint and too little unpainted space were used in each layer

The governing concept is tonal balance in layered negative painting. Each added dark surrounding area increases contrast and visual weight; if the paint is too dark and the remaining unpainted spaces become too small, the composition loses openness and appears heavy. Leaving more white would generally preserve lightness, while brush cleanliness and paper size do not directly create this tonal problem. Hence option B identifies the main cause.