covered by the first, and leave the two in a quiet place where dust will settle upon them, the unprotected margin of the second sheet will in course of time become discolored and show a contrast. Many drawings are so delicate that the dust can not be cleared from them without injuring the drawings themselves. Unfixed charcoals and pastels are the most delicate drawings of all, and require the most perfect protection against dust. The tidy housekeeper who dusts the unfinished charcoal on the easel is alluded to with horror in the little treatises on that art as the most destructive of all its enemies. As the charcoal itself is nothing but unfixed dust, it obeys the housekeeper's feather brush only too readily, and disappears with the other dust that means nothing and is valueless. The housekeeper in such cases seems strikingly like the blind destructive forces of the natural world which respect genius and its productions no more than the commonest matter; she is like the sea which drowns Shelley and rolls the fragment of a Greek statue among its pebbles.
Protection against damp and dust may seem less necessary in the case of oil-pictures, but here also it has its importance. Unquestionably an oil-picture has a much stronger constitution than a water-color, yet it is admitted that some colors used in oil-paintings are affected unfavorably by moisture, and are insufficiently protected by pure oil. De Mayerne affirms that indigo fades in oil without varnish, but is durable under varnish, and the following quotation from Sir Charles Eastlake's "Materials for a History of Oil-Painting" will show the peculiar kind of danger that may arise from damp:
"The effect of moisture on verdigris, even when the color is mixed with oil, as noticed by Leonardo da Vinci, shows that such a vehicle, unless it be half resinified, affords no durable protection to some colors in humid climates; and the efficacy of resinous solutions, as hydrofuges, is at once exemplified by the fact that they answer the end which (unprepared) oil alone is insufficient to accomplish. Colors which are easily affected by humidity require to be protected according to the extent of the evil. Whatever precaution of this kind was requisite in Italy was doubly needed in Flanders. The superficial varnish which sufficed in the extreme case referred to by Leonardo was incorporated with the color by the oil-painters of the North. So in proportion as the Flemish painters adopted a thinner vehicle, the protecting varnish was applied on colors which the Italians could safely leave exposed, at all events till a general varnish was spread over the work. It will be remembered that this last method was unnecessary in the original Flemish process, according to which the colors, being more or less mixed with varnish, and being painted at once, remained glossy, and needed no additional defense."
It would not be safe, however, to conclude from this that a simple coat of varnish is a perfect insurance against damp, for varnish itself may be ultimately penetrated by damp, as Field showed in his chapter
