In art, what term refers to the technique of adding dark areas to an artwork to create the illusion of depth and volume?

What is the term used for the gradual transition from light to dark in a drawing or painting?

What is the name of the shading technique where small dots are used to create texture and value in a drawing or painting?

What is the shading technique that involves using closely spaced parallel lines to create shadow and texture in a drawing or painting?

What is the term for the shading technique where lines intersect at right angles to create a grid-like pattern for shadow and depth?