When creating his silverpoint drawing heads of the virgin and child, raphael employed a process in which the artist uses closely arranged parallel lines to create value.

When creating his silverpoint drawing Heads of the Virgin and Child, Raphael employed "hatching"...

Hatching is a procedure used to make tonal or shading impacts by moving closely dispersed parallel lines. The fundamental idea is that the amount, thickness and dividing of the lines will influence the brilliance of the general picture, and underline frames making the illusion of volume. Hatching lines ought to dependably pursue the frame.

variety in color and variety in texture