white-lead. It has been remarked that a certain kind of decorative work used in the middle ages consisted of paint applied on tin-foil and protected by glass. Here was a double protection against damp, the glass before and the tin-foil behind, the glass answering to the varnish on a picture, but with more complete efficacy.
Glass is now largely used in the National Gallery for the protection of oil-pictures, but, unfortunately, the common objection that it does not allow the spectator to see the picture easily is but too well founded. What we really see is too often the reflection of a group of visitors to the gallery, almost as in a looking-glass. This happens especially when the picture is a dark one, and many of the finest old pictures are dark. We are sometimes told that it is an affair of focusing the eye, and that if we look as we ought to do at the picture itself, and not at the reflections, we shall not see the reflections. What really happens is this: If we look at the reflections of the visitors we see them wonderfully well, down to the most minute inventions of the feminine costume, and if we look at the picture we see it in a confused way intermingled with the reflections. This being so, it follows that private owners are not much encouraged to put their pictures under glass. It may be objected that water-colors are habitually protected in this way, and that no one complains. True, but in the first place, with regard to water-colors we have no choice, as any fly could spoil an unprotected water-color in a minute; in the second place, a drawing in watercolor is usually of small dimensions, so that it is more easily seen; and, lastly, water-colors are generally paler than oil-pictures, so that they do not make such perfect mirrors. A dark old oil-picture with a sheet of plate-glass before it is, in certain lights, almost as good a mirror as if the glass were lined with quicksilver. We can hardly, then, include glass among the means to be recommended for protecting oil-pictures from damp, and must trust rather to the dryness of the atmosphere in which the pictures are kept; and yet it is necessary to avoid excessive heating, which in certain cases produces or favors cracking and destroys by detaching paint from the priming of the canvas.
Canvas may not seem a very durable material, and yet, on the whole, it is preferable to wooden panels, for it may truly be said of wood, as it was said of the arch in architecture, that it is never at rest. It is always either swelling or contracting, and if a composite panel is not quite scientifically constructed, it is sure to tear itself and show fissures. Panels are therefore usually employed for small works only, and for these copper would be better still, though it has been used rarely. If a panel is well painted on the back, it will absorb damp less readily, and this precaution is very easily taken.
The art of removing a painting from an old to a new canvas is now so well understood that the operation, which many years ago seemed formidable, is now performed every day without attracting attention.
