What is the precise value of this system of sculpture, this low relief? Luca della Robbia, and the other sculptors of the school to which he belongs, have before them the universal problem of their art; and this system of low relief is the means by which they meet and overcome the special limitation of sculpture.
That limitation results from the material and other necessary conditions of all sculptured work, and consists in the tendency of such work to a hard realism, a one-sided presentment of mere form, that solid material frame which only motion can relieve, a thing of heavy shadows, and an individuality of expression pushed to caricature. Against this tendency to the hard presentment of mere form trying vainly to compete with the reality of nature itself, all noble sculpture constantly struggles; each great system of sculpture resisting it in its own way, etherealising, spiritualising, relieving its stiffness, its heaviness, and death. The use of colour in sculpture is but an unskilful contrivance to effect, by borrowing from another art, what the nobler sculpture effects by strictly appropriate means.
To get not colour, but the equivalent of colour; to secure the expression and the play of life; to [66] expand the too firmly fixed individuality of pure, unrelieved, uncoloured form:--this is the problem which the three great styles in sculpture have solved in three different ways.
Allgemeinheit--breadth, generality, universality,--is the word chosen by Winckelmann, and after him by Goethe and many German critics, to express that law of the most excellent Greek sculptors, of Pheidias and his pupils, which prompted them constantly to seek the type in the individual, to abstract and express only what is structural and permanent, to purge from the individual all that belongs only to him, all the accidents, the feelings and actions of the special moment, all that (because in its own nature it endures but for a moment) is apt to look like a frozen thing if one arrests it.
In this way their works came to be like some subtle extract or essence, or almost like pure thoughts or ideas: and hence the breadth of humanity in them, that detachment from the conditions of a particular place or people, which has carried their influence far beyond the age which produced them, and insured them universal acceptance.