86 THE POPULAR SCIENCE MONTHLY. 



outer wall, may prevent condensation, because the thin partition, hav- 

 ing 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 paste- 

 board. 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 with- 

 out 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 



