On the question of the causes of the decay noticed and the best methods of preparing leather in the future, I may quote the following:—
“The work of a sub-committee, which was composed of chemists specially conversant with the treatment of leather, was directed specially to the elucidation of the following points: an investigation of the nature of the decay of leather used for bookbinding; an examination of the causes which produced this decay; a research into the best methods of preparing leather for bookbinding; and a consideration of the points required to be dealt with in the preservation of books.
“Taking these points in order, the first one dealt with is the question of the nature of the decay of leather. To arrive at their conclusions on this subject, the sub-committee made a number of tests and analyses of samples of decayed leather bookbindings, as well as of leathers used for binding. The committee found that the most prevalent decay was what they term a red decay, and this they think may be differentiated into old and new, the old red decay being noticeable up to about 1830, and the new decay since that date. In the old decay, the leather becomes hard and brittle, the surface not being easily abraded by friction. The older form is specially noticeable in calf-bound books, tanned presumably with oak bark. The new form affects nearly all leathers, and in extreme cases seems absolutely to destroy the fibres. Another form of deterioration, more noticeable in the newer books, renders the grain of the leather liable to peel off when exposed to the slightest friction. This is the most common form of decay noted in the more recent leathers. In nearly all samples of Russia leather a very violent form of red decay was noticed. In many cases the leather was found to be absolutely rotten in all parts exposed to light and air, so that on the very slightest rubbing with a blunt instrument the leather fell into fine dust....
“The second point is the cause of the decay. An extensive series of experiments was carried out with a view of determining the causes of the decay of bindings. The sub-committee find that this is caused by both mechanical and by chemical influences. Of the latter, some are due to mistakes of the leather manufacturer and the bookbinder, others to the want of ventilation, and to improper heating and lighting of libraries. In some cases inferior leathers are finished (by methods in themselves injurious) so as to imitate the better class leathers, and of course where these are used durability cannot be expected. But in the main the injury for which the manufacturer and bookbinder are responsible must be attributed rather to ignorance of the effect of the means employed to give the leather the outward qualities required for binding, than to the intentional production of an inferior article.... Leathers produced by different tanning materials, although they may be equally sound and durable mechanically, vary very much in their resistance to other influences, such as light, heat, and gas fumes.
“For bookbinding purposes, the sub-committee generally condemn the use of tanning materials belonging to the catechol group, although the leathers produced by the use of these materials are for many purposes excellent, and indeed superior. The class of tanning materials which produce the most suitable leather for this particular purpose belong to the pyrogallol group, of which a well known and important example is sumach. East Indian or ‘Persian’ tanned sheep and goat skins, which are suitable for many purposes, and are now used largely for cheap bookbinding purposes, are considered extremely bad. Books bound in these materials have been found to show signs of decay in less than twelve months, and the sub-committee are inclined to believe that no book bound in these leathers, exposed on a shelf to sunlight or gas fumes, can ever be expected to last more than five or six years. Embossing leather under heavy pressure to imitate a grain has a very injurious effect, while the shaving of thick skins greatly reduces the strength of the leather by cutting away the tough fibres of the inner part of the skin. The use of mineral acids in brightening the colour of leather, and in the process of dyeing, has a serious effect in lessening its resistance to decay. A good deal yet remains to be learned about the relative permanency of the different dyes.”
On analysis free sulphuric acid was found to be present in nearly all bookbinding leather, and it is the opinion of the committee that even a small quantity of this acid materially lessens the durability of the leather.
“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 have examined very many samples of leather manufactured and sold specially for bookbinding purposes, from different factories, bought from different dealers, or kindly supplied by bookbinders and by librarians, and have found them to contain, in a large number of cases, free sulphuric acid, from 0.5 up to 1.6 per cent.”
The publication of the report should tend to fix a standard for bookbinding leather. Hitherto there has been no recognised standard. Bookbinders have selected leather almost entirely by its appearance. It has now been shown that appearance is no test of durability, and the mechanical test of tearing the leather is insufficient. Sound leather should tear with difficulty, and the torn edges should be fringed with long, silky fibres, and any leather which tears very easily, and shows short, curled-up fibres at the torn edges, should be discarded. But though good bookbinding leather will tear with difficulty, and show long fibres where torn, that is in itself not a sufficient test; because it has been shown that the leather that is mechanically the strongest, is not necessarily the most durable and the best able to resist the adverse influences to which books are subject in libraries.
The report shows that bookbinders and librarians are not, as a general rule, qualified to select leather for bookbinding. In the old days, when the manufacture of leather was comparatively simple, a bookbinder might reasonably be expected to know enough of the processes employed to be able to select his leather. But now so complicated is the manufacture, and so many are the factors to be considered, that an expert should be employed.
“The committee have satisfied themselves that it is possible to test any leather in such a way as to guarantee its suitability for bookbinding. They have not come to any decision as to the desirability of establishing any formal or official standard, though they consider that this is a point which well deserves future consideration.”