To determine where values change when light moves over an uneven surface by using a range of values to paint the different values in a realistic, monochromatic self-portrait;
To effectively communicate an image that looks like you through careful examination of the values and structure of your face.
There are a few crucial skills for painting facial features. Such as sizes of the shapes, getting the proportions right. And getting the right values white, gray, and black. The last one being accuracy, how accurate your painting is to your picture.