means of expression among the last refinements of shadow, which are almost invisible except in a strong light, and which the finest pencil can hardly follow. The whole essence of their work is expression, the passing of a smile over the face of a child, the ripple of the air on a still day over the curtain of a window ajar.
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, a limitation which results from the essential conditions and material of all sculptured work, and which consists in the tendency of this 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 that hard presentment of mere form which tries vainly to compete with the reality of nature itself, all noble sculpture is constantly struggling; each great system of sculpture resisting it in its own way, etherealising, spiritualising, relieving its hardness, its heaviness and death. The use of colour in sculpture is but an unskilful contrivance to effect
