shading techniques.
When you understand how shading works, you can begin to draw the illusion of depth. Simply stated, values are various shades of gray. A broad range of different values is the primary ingredient of shading.
value scale.
The value scale is a system of organizing values. It consists of nine values ranging from white to black, with several shades of gray in between. These shades help to create the illusion of depth and three-dimensionality in a work of art.
hatching.
Hatching is a series of straight or curved lines drawn beside one another to give the illusion of a value. Depending on the shading effects you want, you can make the individual lines in hatching sets far apart or close together. In the hatching set in the upper left , you can clearly see each individual hatching line. However, the hatching lines in the second set are drawn closely together to create a more solid ton
stippling.
Stippling is a series of dots drawn beside or atop one another to give an illusion of depth and value. The closer the dots are placed, the darker the area will appear.
crosshatching.
Crosshatching is a shading technique in which one set of lines crosses over another set. In the upper set, the crosshatching lines are far apart and lots of white spaces are visible. Lines that are close together look like a solid tone.