Conventionalism by cause of inefficiency of material.
If, for instance, we are required to represent a human figure with stone only, we cannot represent its colour; we reduce its colour to whiteness. That is not elevating the human body, but degrading it; only it would be a much greater degradation to give its colour falsely. Diminish beauty as much as you will, but do not misrepresent it. So again, when we are sculpturing a face, we can't carve its eyelashes. The face is none the better for wanting its eyelashes--it is injured by the want; but would be much more injured by a clumsy representation of them.
LECTURE III - MODERN MANUFACTURE AND DESIGN - THE TWO PATHS by JOHN RUSKIN