Oil pictures commonly suffer from being attacked at the back by damp from walls on which they may be hung. The canvas on which they are painted is often incapable of resisting moisture, that it not only soon becomes rotten, but the damp finds its way through it, to the colours in the front surface. This form of decay, for the most part, may be prevented, or at least checked, by painting the back of the canvas with a coat of white lead. Painter's canvas is usually prepared by first covering one side of it with a coat of whiting, to which glue size has been added...[therefore it is susceptible to damp from the back] It is not unusual to find the back of a newly painted picture covered with a compact fur, or fungus. In such a case an organic change has taken place in the priming of glue and whiting, the effect of damp on the glue size, and which if not arrested, will ultimately end in the destruction of the picture. Whenever this may have happened a certain damage will have been done to the work which cannot be repaired and this will be more distinctly shown in the course of time, by the paint peeling of the canvas wholesale. In rooms where gas is used for lighting, any textile fabric which may be in them greatly suffers. Indeed, in some instances, a few years are sufficient to effect a complete decay. This is shown by the breaking of picture-cords, window-blind-cords, etc. The backs of oil-pictures on canvas are subject to the same influence. It must therefore be seen that unless they are protected, destruction must ensue.,,It may be said, in answer to this, that oil pictures on canvas may be lined, and relined when necessary; and this is quite true. At the same time, it would be a mistake to suppose that a work escapes injury whenever this is done. The writer is well acquainted with the various processes resorted to for cleaning, restoring and lining pictures, and feels assured that every effort should be made to protect works of art from the necessity of undergoing any operation of this kind. A coat of oil paint, applied to the backs of canvases, will prevent the form of decay alluded to.,