The word value is interesting. It’s origin is Latin, and its basic meaning is strength or worth. In art, value is the relationship of one part of a composition to another in terms of lightness or darkness. Color has value. We’ll deal first with just the value of light and dark as shades of grey.
Value is often also referred to in art as tone. However, the word tone has more varied meanings and can be confusing.
It’s important to note that, while value ranges from brightest white to darkest black in a continuous scale in nature, the artist has maybe 9 or 10 easily distinguishable shades between white and black. Because of that, the artist actually has to “lie” in painting to establish relationships in value. Value, in other words, is relative. (Here, by the way, is where color comes in handy. It can be effective to use color to distinguish an edge where the value of tangential fields is the same.)
To discover this for yourself, do a value scale, using any media—pencil, charcoal, ink, paint—in a series of 9 distinct steps from black to white. Start by delineating 5 steps: white, light grey, medium grey, dark grey and black. Now try to delineate at least 9 steps.