Leather

LEATHER

Of all the materials used by the bookbinders, leather is the most important and the most difficult to select wisely. It is extremely difficult to judge a leather by its appearance.

“We find now, that instead of leather made from sheep, calf, goat, and pigskins, each having, when finished, its own characteristic surface, that sheepskins are got up to look like calf, morocco, or pigskin; that calf is grained to resemble morocco, or so polished and flattened as to have but little character left; while goatskins are grained in any number of ways, and pigskin is often grained like levant morocco. So clever are some of these imitations, that it takes a skilled expert to identify a leather when it is on a book.”

There have been complaints for a long time of the want of durability of modern bookbinding leather, but there has not been until lately any systematic investigation into the causes of its premature decay.

By permission, I shall quote largely from the report of the committee appointed by the Society of Arts to inquire into the subject. There are on this special committee leather manufacturers, bookbinders, librarians, and owners of libraries. The report issued is the result of an immense amount of work done. Many libraries were visited, and hundreds of experiments and tests were carried out by the sub-committees. There is much useful information in the report that all bookbinders and librarians should read. The work of the committee is not yet finished, but its findings may be accepted as conclusive as far as they go.

The committee first set themselves to ascertain if the complaints of the premature decay of modern bookbinding leather are justified by facts, and on this point report that:—

“As regards the common belief that modern binding leather does decay prematurely, the sub-committee satisfied themselves that books bound during the last eighty or hundred years showed far greater evidence of deterioration than those of an earlier date. Many recent bindings showed evidence of decay after so short a period as ten, or even five years. The sub-committee came to the conclusion that there is ample justification for the general complaint that modern leather is not so durable as that formerly used. To fix the date of the commencement of this deterioration was a difficult matter; but they came to the conclusion that while leather of all periods showed some signs of decay, the deterioration becomes more general on books bound after 1830, while some leathers seem to be generally good until about 1860, after which date nearly all leathers seem to get worse. The deterioration of calf bindings at the latter end of the 19th century may be attributed as much to the excessive thinness as to the poor quality of the material.”

The committee endeavoured to ascertain the relative durability of the leathers used for bookbinding, and after visiting many libraries, and comparing bindings, they report as follows:—

“As to the suitability of various leathers, the sub-committee came to the conclusion that of the old leathers (15th and 16th century), white pigskin, probably alum ‘tanned,’ is the most durable, but its excessive hardness and want of flexibility renders this leather unsuitable for most modern work. Old brown calf has lasted fairly well, but loses its flexibility, and becomes stiff and brittle when exposed to light and air. Some of the white tawed skins of the 15th and 16th century, other than white pigskin, and probably deerskin, have lasted very well. Some 15th and 16th century sheepskin bindings have remained soft and flexible, but the surface is soft, and usually much damaged by friction. Vellum seems to have lasted fairly well, but is easily influenced by atmospheric changes, and is much affected by light. Early specimens of red morocco from the 16th to the end of the 18th century were found in good condition, and of all the leathers noticed, this seems to be the least affected by the various conditions to which it had been subjected. In the opinion of the committee, most of this leather has been tanned with sumach or some closely allied tanning material. Morocco bindings earlier than 1860 were generally found to be in fairly good condition, but morocco after that date seems to be much less reliable, and in many cases has become utterly rotten. During the latter part of the 18th century it became customary to pare down calf until it was as thin as paper. Since about 1830 hardly any really sound calf seems to have been used, as, whether thick or thin, it appears generally to have perished. Sheepskin bindings of the early part of the century are many of them still in good condition. Since about 1860 sheepskin as sheepskin is hardly to be found. Sheepskins are grained in imitation of other leathers, and these imitation-grained leathers are generally found to be in a worse condition than any of the other bindings, except, perhaps, some of the very thin calfskin. Undyed modern pigskin seems to last well, but some coloured pigskin bindings had entirely perished. Modern leathers dyed with the aid of sulphuric acid are all to be condemned. In nearly every case Russia leather was found to have become rotten, at least in bindings of the last fifty years.”

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.”

It is to be hoped that some system of examining and hall-marking leather by some recognised body, may be instituted. If librarians will specify that the leather to be employed must be certified to be manufactured according to the recommendations of the Society of Arts Committee, there is no reason why leathers should not be obtained as durable as any ever produced. This would necessitate the examining and testing of batches of leather by experts. At present this can be done more or less privately at various places, such as the Yorkshire College, Leeds, or the Herolds’ Institute, Bermondsey. In the near future it is to be hoped that some recognised public body, such as one of the great City Companies interested in leather, may be induced to establish a standard, and to test such leathers as are submitted to them, hall-marking those that come up to the standard. This would enable bookbinders and librarians, in ordering leather, to be sure that it had not been injured in its manufacture. The testing, if done by batches, should not add greatly to the cost of the leather.

On the question of the qualities of an ideal bookbinding leather the committee report:—

“It is the opinion of the committee, that the ideal bookbinding leather must have, and retain, great flexibility.... (It) must have a firm grain surface, not easily damaged by friction, and should not be artificially grained.... The committee is of opinion that a pure sumach tannage will answer all these conditions, and that leather can, and will, be now produced that will prove to be as durable as any made in the past.”

The committee has so far only dealt with vegetable-tanned leather. I have used, with some success, chrome-tanned calfskin. Chrome leather is difficult to pare, and to work, as it does not become soft when wet, like vegetable-tanned leather. It will stand any reasonable degree of heat, and so might perhaps be useful for top-shelf bindings and for shelf edging. It is extremely strong mechanically, but without further tests I cannot positively recommend it except for trial.

While the strength and probable durability of leather can only be judged by a trained leather chemist, there remains for the binders selection, the kind of leather to use, and its colour.

Most of the leather prepared for bookbinding is too highly finished. The finishing processes add a good deal to the cost of the leather, and are apt to be injurious to it, and as much of the high finish is lost in covering, it would be better for the bookbinder to get rougher leather and finish it himself when it is on the book.

The leathers in common use for bookbinding are:—

• Goatskin, known as morocco.
• Calf, known as calf and russia.
• Sheepskin, known as roan, basil, skiver, &c.
• Pigskin, known as pigskin.
• Sealskin, known as seal.

Morocco is probably the best leather for extra binding if properly prepared, but experiment has shown that the expensive Levant moroccos are nearly always ruined in their manufacture. A great many samples of the most expensive Levant morocco were tested, with the result that they were all found to contain free sulphuric acid.

Calf.—Modern vegetable-tanned calf has become a highly unsatisfactory material, and until some radical changes are made in the methods of manufacturing it, it should not be used for bookbinding.

Sheepskin.—A properly tanned sheepskin makes a very durable, though rather soft and woolly, leather. Much of the bookbinding leather now made from sheepskin is quite worthless. Bookbinders should refuse to have anything to do with any leather that has been artificially grained, as the process is apt to be highly injurious to the skin.

Pigskin.—Pigskin is a thoroughly good leather naturally, and very strong, especially the alumed skins; but many of the dyed pigskins are found to be improperly tanned and dyed, and worthless for bookbinding.

Sealskin is highly recommended by one eminent librarian, but I have not yet had any experience of its use for bookbinding.

The leather that I have found most useful is the Niger goatskin, brought from Africa by the Royal Niger Company; it is a very beautiful colour and texture, and has stood all the tests tried, without serious deterioration. The difficulty with this leather is that, being a native production, it is somewhat carelessly prepared, and is much spoiled by flaws and stains on the surface, and many skins are quite worthless. It is to be hoped that before long some of the manufacturers interested will produce skins as good in quality and colour as the best Niger morocco, and with fewer flaws.

Much leather is ruined in order to obtain an absolutely even colour. A slight unevenness of colours is very pleasing, and should rather be encouraged than objected to. That the want of interest in absolutely flat colours has been felt, is shown by the frequency with which the binders get rid of flat, even colours by sprinkling and marbling.

On this point I may quote from the committee: “The sprinkling of leather, either for the production of ‘sprinkled’ calf or ‘tree’ calf, with ferrous sulphate (green vitriol) 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. Iron acetate or lactate is somewhat less objectionable, but probably the same effects may be obtained with aniline colours without risk to the leather.”