The draperies with which you dress figures ought to have their folds so
accommodated as to surround the parts they are intended to cover; that
in the mass of light there be not any dark fold, and in the mass of
shadows none receiving too great a light. They must go gently over,
describing the parts; but not with lines across, cutting the members
with hard notches, deeper than the part can possibly be; at the same
time, it must fit the body, and not appear like an empty bundle of
cloth; a fault of many painters, who, enamoured of the quantity and
variety of folds, have encumbered their figures, forgetting the
intention of clothes, which is to dress and surround the parts
gracefully wherever they touch; and not to be filled with wind, like
bladders puffed up where the parts project. I do not deny that we ought
not to neglect introducing some handsome folds among these draperies,
but it must be done with great judgment, and suited to the parts, where,
by the actions of the limbs and position of the whole body, they gather
together. Above all, be careful to vary the quality and quantity of your
folds in compositions of many figures; so that, if some have large
folds, produced by thick woollen cloth, others being dressed in thinner
stuff, may have them narrower; some sharp and straight, others soft and
undulating.
_Leonardo._