essential purpose of the sculptor.  The chief reason why the terra-cotta bust of St. John at Berlin looks flippant and fastidious is, that the painter was indiscreet in drawing the eyebrows and lips:  owing to his carelessness, they do not coincide with the features indicated by the modeller, and the entire character of the boy is consequently changed.  The question of polychromacy in Donatello’s sculpture is of great importance, and requires some notice.  It is no longer denied that classical statues were frequently coloured.  The Parthenon frieze and many celebrated monuments of antiquity were picked out with colour.  Others received some kind of polish, circumlitio,—­like the dark varnish which is on the face of the Coscia effigy.  Again, the use of ivory, precious stones, and metal was common.  The lips and eyeballs were frequently overlaid by thin slabs of silver.[160] The origin of polychromacy, doubtless, dates back to the most remote ages.  It was first needed to conceal imperfections, and to supply what the carver felt his inability to render.  It connotes insufficiency in the form.  The sculptor, of all people, ought to be able to see colour in the uncoloured stone:  he ought to realise its warmth, texture and shades.  Nobody has any right to complain that a statue is uncoloured:  the substance and quality of the marble is in itself pleasing, but relative truth is all that is required in a portrait-bust.  If one wants to know the colour of a man’s eye, or the precise tint of his complexion, the painter’s art should be invoked, but only where its gradations and subtleties can be fully rendered—­on the canvas.  Polychromacy is a mixture of two arts:  it is one art trying to steal a march upon another art by producing illusion.  That is why the pantaloon paints his face, and why the audience laughs:  the spirit which tolerates painted statues ends by adorning them with necklaces.  Donatello, whose sense of light and shade was acutely developed, least required the adventitious aid of colour.  Polychromacy was to a certain extent justified on terra-cotta, to soften the toneless colour of the clay, and on wood it served a purpose in hiding the cracks of a brittle substance.  Nowadays it is happily no more than a refugium peccatorum.  There is, however, no doubt that in Donatello’s day it was widely used, and used by Donatello himself.  It began in actual need, then became a convention, and long survived:  il n’y a rien de plus respectable qu’un ancien abus.  During the fifteenth century statues were coloured during the highest proficiency of sculpture:  buildings were painted,[161] and bronze was habitually gilded.  Donatello’s Coscia, and his work at Siena and Padua, still show signs of it.  The St. Mark was coloured, and the Cantoria was much more brilliant with gold than it is now.  The St. Luke, which was removed from Or San Michele,[162] has long been protected from the weather, and still shows traces of a rich brocade decorated with coloured lines.