What is a grisaille, and why paint one first?
Short answer: A grisaille is a painting made only in greys or a single neutral color, so the whole image is built from value alone. Painting one first lets you solve drawing, light and form before color adds a second set of decisions.
The idea
The word comes from the French gris, grey. In a grisaille every passage is judged only by how light or dark it is. If the grisaille reads as a convincing form, color laid over it has a solid structure to sit on.
Why it still matters
Most failed paintings fail in value, not color. A face with correct values and odd color still looks like a face. A face with lovely color and wrong values looks flat or confused. The grisaille isolates the part that matters most.
How to paint one
Mix a short value scale from ivory black and white, often five to seven steps, before you begin. Block in the shadow shapes as one mass, then the halftones, then the lights. Keep edges soft where form turns gently and firm where planes meet.
Let it dry, then glaze or paint color over it, or simply treat it as a finished study. Both are legitimate. Clint Atelier uses grisaille studies as the value before color step in its teaching.