You can read the rest for yourselves. Grisaille is a separate branch of colour-decoration which belongs with the whole system of lighting and fenetrage, and will have to remain a closed book because the feeling and experience which explained it once are lost, and we cannot recover either. Such things must have been always felt rather than reasoned, like the irregularities in plan of the builders; the best work of the best times shows the same subtlety of sense as the dog shows in retrieving, or the bee in flying, but which tourists have lost. All we can do is to note that the grisailles were intended to have values. They were among the refinements of light and colour with which the apse of Chartres is so crowded that one must be content to feel what one can, and let the rest go. Understand, we cannot! nothing proves that the greatest artists who ever lived have, in a logical sense, understood! or that omnipotence has ever understood! or that the utmost power of expression has ever been capable of expressing more than the reaction of one energy on another, but not of two on two; and when one sits here, in the central axis of this complicated apse, one sees, in mere light alone, the reaction of hundreds of energies, although time has left only a wreck of what the artist put here. One of the best window spaces is wholly filled up by the fourteenth-century doorway to the chapel of Saint Piat, and only by looking at the two windows which correspond on the north does a curious inquirer get a notion of the probable loss. The same chapel more or less blocks the light of three other principal windows. The sun, the dust, the acids of dripping water, and the other works of time, have in seven hundred years corroded or worn away or altered the glass, especially on the south side. Windows have been darkened by time and mutilated by wilful injury. Scores of the panels are wholly restored, modern reproductions or imitations. Even after all this loss, the glass is probably the best-preserved, or perhaps the only preserved part of the decoration in colour, for we never shall know the colour- decoration of the vaults, the walls, the columns, or the floors. Only one point is fairly sure;--that on festivals, if not at other times, every foot of space was covered in some way or another, throughout the apse, with colour; either paint or tapestry or embroidery or Byzantine brocades and Oriental stuffs or rugs, lining the walls, covering the altars, and hiding the floor. Occasionally you happen upon illuminated manuscripts showing the interiors of chapels with their colour-decoration; but everything has perished here except the glass.