Lectures on Art by John Ruskin

146. The plan of the divisions of art-schools which I gave you in the last lecture is of course only a first germ of classification, on which we are to found farther and more defined statement; but for this very reason it is necessary that every term of it should be very clear in your minds.

And especially I must explain, and ask you to note the sense in which I use the word "mass. " Artists usually employ that word to express the spaces of light and darkness, or of colour, into which a picture is divided. But this habit of theirs arises partly from their always speaking of pictures in which the lights represent solid form. If they had instead been speaking of flat tints, as, for instance, of the gold and blue in this missal page, they would not have called them "masses," but "spaces" of colour. Now both for accuracy and convenience' sake, you will find it well to observe this distinction, and to call a simple flat tint a space of colour; and only the representation of solid or projecting form a mass.