outer wall, may prevent condensation, because the thin partition, having little substance, rises easily in temperature. It would be quite worth while, in a house where valuable works of art are hung, to have thin inner walls with a circulation of warmed air between them and the thick external wall of-the building. Tapestry is a very effective remedy against visible condensation, as it absorbs a great quantity of water, which it afterward gives off slowly into the atmosphere, and it may prevent or greatly diminish real condensation by being more easily warmed than a mass of stone can be.
The evil of injury from damp ought, however, to be combated as much as possible in the framing of the pictures and prints themselves. I will begin with prints because they are more common, so that the preservation of them concerns a greater number of my readers. In the first place, I would never trust to a backing of mill-board or pasteboard. A print may appear to be safe with such a backing for years, and then there may be a damper winter than usual, or you may go and live in a damper house, or you may be absent, and the house may not be heated with sufficient regularity, with the result of unexpected injury to your print. Why not make it safe from the beginning? It is easy to do this, so that the print may be hung on a damp wall without danger. Instead of mill-board put sheet-zinc for a backing. It need not be thick, and you can always get a piece of sheet-zinc as big as the largest print. By way of completing precautions I am careful to expel any moisture there may be in the print itself by heating it well over a spirit-lamp before inclosing it between the zinc and the glass, and instead of ordinary paste for the slips of paper that join the glass to the inside of the frame and the backing to the back of the frame I employ a strong solution of gum-lac in spirits of wine, which is impervious to moisture. The print is thus inclosed in a little space that is not only water-tight, but even air-tight as well, so that damp air can not get to it. I have tried the experiment of hanging prints so framed against the dampest walls that I could find, and they have passed more than one wet winter in perfect safety, while prints framed in the usual manner, with mill-board backings, were soon spoiled by mildew and rust-spots when hung upon the same walls. All that has just been said about the protection of framed prints applies with still greater force to water-color drawings, as a water-color is far more delicate in its constitution than a print, and therefore much less easily restored to its first appearance after it has been damaged by mildew.
Engravings can not be injured at all by light, the only effect of which is to bleach slightly the paper on which they are printed, but it appears to be quite an ascertained fact that water-color drawings fade when they are painted in full colors, though water-color monochromes in sepia, bistre, or Indian-ink may resist light almost indefinitely. If, then, the object is to preserve water-colors for future generations, they ought to be kept in cabinets; but it is also intelligible that the owner
