or only a part, of their bays.  In the latter case, the grisailles are reserved for the side windows which are meant to be seen obliquely, and in that case the coloured glass fills the bays of the fond, the apsidal openings which are meant to be seen in face from a distance.  These lateral grisailles are still opaque enough to prevent the solar rays which pass through them from lighting the coloured windows on the reverse side; yet, at certain hours of the day, these solar rays throw a pearly light on the coloured windows which gives them indescribable transparence and refinement of tones.  The lateral windows in the choir of the Auxerre Cathedral, half-grisaille, half-coloured, throw on the wholly coloured apsidal window, by this means, a glazing the softness of which one can hardly conceive.  The opaline light which comes through these lateral bays, and makes a sort of veil, transparent in the extreme, under the lofty vaulting, is crossed by the brilliant tones of the windows behind, which give the play of precious stones.  The solid outlines then seem to waver like objects seen through a sheet of clear water.  Distances change their values, and take depths in which the eye gets lost.  With every hour of the day these effects are altered, and always with new harmonies which one never tires of trying to understand; but the deeper one’s study goes, the more astounded one becomes before the experience acquired by these artists, whose theories on the effects of colour, assuming that they had any, are unknown to us and whom the most kindly-disposed among us treat as simple children.

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