The second cause of trouble is the manufacture of leather from skins from distant lands which have been improperly or insufficiently preserved for export. It often happens that the fibres have partly perished before the tanner receives the skins, the resulting leather is therefore poor, spongy, and partially perished, making thin leather, which sometimes, on account of its thinness, will cut up apparently economically for the binder, but not economically for the librarian or the owner of books, as the leather cannot possibly be as good or have as long life as leather manufactured from a sound skin.
Bright even shades and light fancy colours previous to the introduction of acid bleaches were manufactured from sumach-tanned skins only, sumach alone producing a leather of a light cream colour, and therefore capable of taking practically any shade of dye. Most other tanning materials produced dark foundations, on which it was practically impossible to dye any but a dark shade. Gradually, however, manufacturers found leather tanned with materials cheaper than sumach could be scoured and bleached with acids, then re-tanned with sumach, thus producing a light, even-coloured leather, which with the dye produced light shades. The cheapest, and at the same time the most effective, acid for this purpose was vitriol or sulphuric acid. This, in common with other mineral acids, combines with the leather fibre, upon which it exercises a most disastrous and disintegrating action, and to the use of this acid, either as a bleaching or clearing agent in the tanning process, or in subsequent use in developing the colour in the dye-bath, may be ascribed the cause of decay of over 90 per cent. of modern bookbinding and upholstering leather. It is impossible to remove these acids from leather by any subsequent amount of washing, or without the addition of some other chemical to expel them. Recently the writer treated some leather with sulphuric acid, and after cutting the leather up into small pieces, washed the same in running water for three weeks; at the end of that period the sulphuric acid was still tightly fixed in the fibres of the leather.
The introduction of aniline dyes instead of the older process of wood dyes made a great change in the production of bookbinding leather. Hundreds of new shades of colour were produced, and the process of leather dyeing was simplified and cheapened. But, unfortunately, in the use of a certain class of these dye-stuffs the full depth of shade could not at that date be produced upon the leather except in the presence of an acid. Here, again, therefore, sulphuric acid was introduced into the leather during the process of manufacture, thus increasing the proportion of leather which contained this disintegrating material. It has frequently been stated by leather dyers and others that a certain quantity of sulphuric acid must be used with acid dye-stuffs, otherwise the full depth of shade cannot be produced, and they claim that without its use it is impossible to produce certain brilliant shades of colour. These statements have been proved to be devoid of foundation. There are several substitutes for sulphuric acid which are harmless in their nature. Among these I may mention formic, acetic and lactic acids. These are organic acids which have no harmful action on the leather; they are easily washed out, and even if any trace of these acids be left in the skin, they will evaporate. Formic acid has even been proved to be cheaper than sulphuric, and, moreover, is capable of developing equal shades in all cases, and deeper and more brilliant shades of colour with some dyes. For the present, however, bookbinders, and especially librarians, are advised not to insist upon brilliant shades of colour.
The introduction of the splitting machine and the introduction of a machine for shaving leather has undoubtedly tended to produce a large quantity of thin leather, but it is impossible either to shave or to split a skin without cutting the network of fibres, and the strength of the leather cannot but be materially decreased. Leather is made up of a complex system of fibres interweaving and intertwining in every possible direction, and even the small amount of paring carried out by the bookbinder himself considerably impairs the strength and life of the binding. How much more, therefore, does the splitting and shaving that the tanner carries out in order to bring the skin to an even substance destroy the strength of the product.
Sufficient has been written on the printing of morocco, seal, and pig grains upon skins of an inferior class, but it cannot be too strongly pointed out to librarians that the strength of embossed leather must be impaired when it is realised how the embossing and printing is carried out. The skins to be embossed are coated over in the wet state with a mixture of dye, size, and other materials, and are then passed between two hot electrotype rollers. This embosses or prints upon the skin the required grain; at the same time it glues the fibres of the leather together, preventing the free run which good skins should possess, and the heat dries up the leather, reducing its strength very considerably.
I now come to the stripping, scouring, souring, and re-tanning of leather. It is difficult to decide whether more damage is done in this process or in the use of mineral acids in the dye-bath; but it is certain that any leather which is stripped of its natural tanning by use of alkalies or bleached by an acid has lost at least 90 per cent. of its wearing and lasting properties. Thousands of dozens of skins in the rough tanned condition reach the English market from India, Australia, New Zealand, and other parts. These are tanned with quebracho, mimosa, or some similar tanning material, whereas the Indian skins are nearly all tanned with turwar bark and are of a reddish-fawn shade of colour. These are purchased by the leather finishers, and are manufactured in England. In order to get rid of the reddish colour they are first soaked in water and afterwards drummed in a weak solution of washing soda, borax, or some similar alkali. This removes the uncombined tan from the skin, as well as taking out the natural grease. The skins emerge from the drum a dark mahogany colour; they are then washed in water and afterwards soured in a sulphuric acid bath. This bleaches the skin to a light bright shade. The finisher then, in order to put back tannin into the skin of a light colour, re-tans them in sumach or a mixture of sumach and oak. They are now known as re-tanned skins; and after drying, are dyed and finished in the ordinary manner. The sheep and goat skins are sold as roans or moroccos, as the case may be, and, as a rule, no indication is given that these are re-tanned skins. The re-tanned Indian skins, however, generally leave the factory as persian roans or persian morocco, but as the skins pass from the manufacturer to the merchant, from the merchant to the small dealer, the word “persian” is generally omitted, and they reach the bookbinder as moroccos or roans, as the case may be. Now this is the most important point for the binder. I would go so far as to say that it should almost be a punishable offence to use either persians or re-tanned skins for bookbinding purposes, as such leather cannot possibly last ten years if exposed to light and air. Not only has the scouring and alkali a perishing effect upon the leather, but it is afterwards made worse by the treatment with acid, a bleach, and the further addition of acid to the dye-bath; added to which the alkaline treatment removes the natural grease or nourishment of the skin, and it is well known to those engaged in the leather trade that the strength and life of a leather is at least doubled by a proper nourishment of the leather with a suitable fat. Therefore, if the whole of the natural fat is removed, the leather rapidly dries, it loses its elasticity and spring, the grain cracks, and after keeping in a dry library for some time the backs break right off the books.
I have dealt with the eight chief causes of premature decay, but before passing to the other part of this paper I must also deal with the weaknesses of the bookbinder as well as those of the leather manufacturer, and, for reasons stated above, absolutely condemn the undue paring of leather, the bleaching of leather by means of oxalic acid, and the use of patent finishes and glares, the composition of which is in most cases a mystery, many of them containing acids, others containing drying agents which have almost as injurious an action upon leather as the vitriol used by the tanner.
To revert to my original thesis, it is not only possible to obtain a leather as good as any leather manufactured from the 16th to 18th century, but it is even possible to get a better leather. Librarians, in drawing up their binding specifications have only to do what the Controller of H.M.’s Stationery Office is doing for the libraries under his charge, viz., to provide under suitable penalties that leathers supplied by the contractor shall be equal to samples shown on pattern cards prior to tendering for the contract, and in addition to insist that such leathers shall conform to certain conditions laid down in the Report of the Society of Arts’ Committee on Bookbinding, which may be summarised as follows:—
1. The binder undertakes not to use stripped and re-tanned leather, whether persians (East Indian skins) or from elsewhere, or to use leather embossed or grained artificially to resemble morocco, pigskin, &c.
2. He guarantees (or undertakes to produce the guarantee of the firm supplying the leather) that all skins supplied (1) are genuine as described; (2) are tanned with pure sumach or galls, or in the case of calf or sheep with oak bark, or mixtures of oak bark and sumach; (3) that no mineral acid has been used either in the process of tanning, bleaching, or dyeing, and that the leather is free from acid or other injurious ingredient; (4) that he will use no acid to clear the leather in the process of binding.