Portraiture may be great art. There is a sense, indeed, in which it is
perhaps the greatest art of any. And portraiture involves expression.
Quite true, but expression of what? Of a passion, an emotion, a mood?
Certainly not. Paint a man or a woman with the damned "pleasing
expression," or even the "charmingly spontaneous" so dear to the
"photographic artist," and you see at once that the thing is a mask, as
silly as the old tragic and comic mask. The only expression allowable in
great portraiture is the expression of character and moral quality, not
of anything temporary, fleeting, and accidental. Apart from portraiture
you don't want even so much, or very seldom: in fact, you only want
types, symbols, suggestions. The moment you give what people call
expression, you destroy the typical character of heads and degrade them
into portraits which stand for nothing.
_Burne-Jones._