“We must absolutely condemn the use of any but mild vegetable acids in souring or scouring the leather, or in the dye bath, and as far as possible would avoid the use of acids and alkalis on tanned leather, both being equally injurious.
“It has been shown by careful experiment, that even a minute quantity of sulphuric acid used in the dye bath to liberate the colour, is at once absorbed by the leather, and that no amount of subsequent washing will remove it. In a very large proportion of cases, the decay of modern sumach-tanned leather has been due to the sulphuric acid used in the dye bath, and retained in the skin....
“We ... advise that the glazing of skins by friction in a damp ‘seasoned’ condition should be avoided.
“The use of nitric acid as a preparation for glazing is absolutely destructive....
“The use of oxalic acid for washing backs of books, or of leather for bookbinding, is fatal to their durability....
“The sprinkling of leather with ferrous sulphate (green vitriol), either for the production of ‘sprinkled’ calf or ‘tree’ calf, must be most strongly condemned, as the iron combines with and destroys the tan in the leather, and free sulphuric acid is liberated which is still more destructive....
“The stretching of leather tightly over books in a wet condition ... should be strongly condemned....
“It is shown conclusively that the catechol tannins, which include turwar, quebracho, hemlock and larch barks, and gambier, are unsuitable for bookbinding leathers where durability is expected, and that sumach yields a much more permanent leather, while myrobalans occupy an intermediate place, but nearly approaching sumach. It is unfortunate
that cassia bark, which is the tanning material employed for East Indian sheep and goat skins, should have proved so unreliable, since these leathers have been largely used in bookbinding without suspicion, and are in other respects a cheap and good article. With regard to sumach leathers themselves, it is possible that some of the darkening noticed may be due to the presence of adulterants, such as pistacia leaves, in the sumach used, as it is almost impracticable to obtain absolutely pure sumach, and the pistacia tannin is allied to that of the cassia.
“Of all the influences to which books are exposed in libraries, gas fumes—no doubt because of the sulphuric and sulphurous acid which they contain—are shown to be the most injurious, but light and especially direct sunlight and hot air, are shown to possess deleterious influences which had scarcely been suspected previously, and the importance of moderate temperature and thorough ventilation of libraries cannot be too much insisted on.”