Ruskin on Pictures, pp.23-4: notes from John Ruskin's review of Cimabue's Celebrated Madonna in the 1855 Royal Academy Exhibition:

"This is a very important and very beautiful picture. It has both sincerity and grace, and is painted on the purest principles of Venetian art - that is to say, on the calm acceptance of the whole of nature, small and great, as, in its place, deserving of faithful rendering. The great secret of the Venetians was their simplicity. [...] Everything in [their art] is done as well as it can be done. Thus, in the picture before us, in the background is the Church of San Miniato, strictly accurate in every detail; on the top of the wall are oleanders and pinks, as carefully painted as the church; the architecture of the shrine on the wall is well studied from thirteenth-century Gothic, and painted with as much care as the pinks; the dresses of the figures, very beautifully designed, are painted with as much care as the architecture; and the faces with as much care as the dresses - that is to say, all things, throughout, with as much care as the painter could bestow. [...]
    The painting before us has been objected to, because it seems broken up into bits. Precisely the same objection would hold, and in very nearly the same degree, against the best works of the Venetians. All faithful colourists' work, in figure-painting, has a look of sharp separation between part and part. [...] Although, however, in common with all other works of its class, it is marked by these sharp divisions, there is no confusion in its arrangement. The principal figure is nobly principal, not be extraordinary light, but by its own pure whiteness; and both the master and the young Giotto attract full regard by distinction of form and face. The features of the boy are carefully studied, and are indeed what, from the existing portraits of him, we know those of Giotto must have been in his youth. The head of the young girl who wears the garland of blue flowers is also very sweetly conceived. [...]"

Ruksin also associated Leighton's painting with lines from the Mrs. Elizabeth Barrett Browning's Casa Guidi Windows:

          "I hold, too,
    That Cimabue smiled upon the lad
    At the first stroke which passed what he could do;
    Or else his Virgin's smile had never had
    Such sweetness in't."

Royal Collection, Windsor Castle