CLEANING THE COVER. It is possible, without being obliged to touch the boards of a book, to clean and repair the covering, either entirely or in spots. To accomplish this, I know some methods which are simple and practical, although, of course, too imperfect to restore to an ancient binding all the brightness and vigor of its youth. A rather mature prima-donna may, perhaps, within certain limits, soften the ravages of time; but, when observed closely, the lines on her face cannot be concealed. And this is also the case with the coquettish old bindings of which I speak.
Morocco or calf which has become soiled by constant handling may be cleaned with a fine sponge dipped in a jelly of white soap. If there are spots of oil or grease, this soap will not suffice; it will be necessary to use black soap, or perhaps a weak solution of some alkali, such as potash or ammonia. In using such alkalis, it is best to first try them on some odd pieces of leather of the same color or upon some part of the bindings not likely to be noticed, because certain colors in leather are apt to decompose or change their tint under the action of an alkali. It has been observed that alkalis tend to darken the leather, more or less; therefore, after employing them, a little acidified water must be applied to neutralize their effect. Also that morocco should be moistened only very slightly, as, otherwise, the surface grain may be smoothed away.
One might begin by trying benzine; this liquid will not attack any color or, at least, only a color formed principally of fatty or resinous substances. Benzine does not act like an alkali; it does not saponify the greasy body, but it dissolves it as water dissolves a salt, a gum or gelatine. It must be used quickly, as it evaporates much more rapidly than ammonia, which itself is considered volatile. The latter will mix with water, but benzine combines only with alcohol.
Thus benzine, like all other essential oils, operates only as a dissolvent and, after having been applied, either pure or mixed with alcohol, upon the book cover, it must be wiped off with a soft cloth before it evaporates, so that the particles of grease which it has dissolved, but not decomposed, will not sink again into the leather and later reappear on its surface.
The best method, after having poured some drops of the liquid upon one side of the book, is to turn this side toward the ground. In this position the benzine, charged with part of the greasy substance, will run down and accumulate upon the lowest edge of the cover, from which it can quickly be wiped off with the substances it holds in solution. Perhaps an even better method of operation may be discovered.
This manner of employing benzine, alcohol or turpentine as dissolvents for the greasy body is equally applicable for removing oily spots from prints, and I recommend it to the reader for experiment. When grease is removed with alkaline water, it is useless to proceed in this manner; the soapy substance which forms on the leather after rubbing should be removed with a damp sponge, after which the book should be dried in the air and then placed under pressure.
Fresh spots of oil or grease may sometimes be removed by impalpable powders of some clay-like nature, absorbent and slightly alkaline.
A spot of ordinary black ink upon morocco, sheepskin, calf or smooth parchment, loses its color when touched with a few drops of sorrel salt or oxalic acid; but I will repeat here the advice already given that these substances may alter certain colors and that it is best to first try them on extra pieces of leather. If the tint lightens or changes only slightly, the spot can be retoned and brightened simply with properly mixed water-colors, after having neutralized, with an alkali, the traces of the acid.
The yellowish spot which remains after the black ink has disappeared is not very noticeable upon brown or yellowish skins, but on vellum or parchment it is more or less apparent. How can this be removed? For if one is obliged to prolong the action of the oxalic acid on the iron oxide which causes it, this portion of the skin not only loses its gloss, but also becomes subject to a more or less rapid process of dissolution.[10]
When the spots are of Chinese ink, old or recent, and have sunk into the texture, as sometimes happens, they resist all known agents.