CHAPTER II.
Why do modern leather bindings decay? Is it possible to obtain a leather for bookbinding purposes as good and as durable as the leather produced from the 16th to 18th century? These are the two problems which the Committee on Bookbinding Leather appointed by the Society of Arts set themselves to investigate. Fortunately we are able to solve both problems.
In the olden days all skins were tanned with a liquor made from either oak bark or sumach, and in some cases a mixture of the two. The skins used by the tanner were usually obtained direct from the butchers. After soaking and cleansing they were then limed for a period sufficiently long to loosen the hair. After the removal of the hair and superfluous flesh and fat, the skins were washed in several changes of fresh soft water to remove the excess of lime, the process being assisted by working the skins over on a beam with a blunt knife. When in suitable condition they were brought into sour, old tan liquors. There was no hurry, the skins being slowly tanned in weak infusions, and when the process was complete, the leather was simply washed free from superfluous tan, dyed with wood or other vegetable dyes, rinsed free from excess of dye-stuff, and dried out. The leather was afterwards softened by stretching, and polished or glazed by brushing the skin over with oil, soap, beeswax, or a solution of some moss. Such leather lacked the high finish, the regular colour, the bright shades of modern leather, but it lasted fifty or one hundred years with hard wear, and, under favourable conditions, appears to be almost imperishable.
The finish, or general appearance, of leather continued to improve up to about 1850, but after that date some of the bindings examined showed signs of rapid deterioration in quality. This deterioration increased on bindings subsequent to 1870, and probably 75 per cent. of the leather used for bookbinding during the last twenty years either has already decayed or will do so within a comparatively short time.
Now to deal with the answer to the first question, Why do modern leather bindings decay? The chief causes are as follows:--
1. The introduction of tanning materials other than oak and sumach, stronger in tanning, and more rapid in their action. Many of these tanning materials are unstable, and the leather produced disintegrates on exposure to light and air.
2. The use of dried and cured skins of variable soundness imported from abroad. Goat, calf, and sheep skins are imported into this country from all over the world; some are simply dried in the sun, some salted, whilst others are cured with various ingredients.
3. The use of infusions of acids and other bleaching agents to produce bright and even shades of colour.
4. The use of sulphuric or other mineral acids for the purpose of developing the depth of colour during the process of dyeing.
5. The shaving and splitting of skin for producing an even substance.
6. Printing and embossing grains upon leather, together with other methods of finishing now in common use.
7. The stripping, scouring, souring, and re-tanning of East India leathers (Persians).
8. The removal of the natural grease or nourishment of the skin.
These eight causes, although by no means exhaustive, are, however, the chief factors in the deterioration of modern leather; and in as few words as possible I will explain the reason of their introduction and effect.
As the industry advanced there were found in different parts of the world tanning materials other than oak and sumach, some of which were two, three, or five times as rich in tannin as oak, thus making infusions of greater strength, and consequently of quicker action, with the result that leather which formerly required from three to six months to tan was turned out in almost as many days, or, at the most, in as many weeks. It was not realised, however, that these different tanning materials contained tannins of different qualities, capable of producing quite a different leather to that produced by means of oak or sumach. The experts who spent months testing and investigating this question came to the unanimous conclusion that the speed of tannage or the strength of the tanning liquor had very little to do with the wearing qualities of the leather produced, but found that some of these new materials contained tannins of a different chemical nature from that of sumach, and that they produced leather of an unstable character, some of the leathers undergoing change in a few hours on exposure to strong light and air. On the other hand, some of the new tanning materials produced permanent leathers practically equal to sumach. Those tanning materials, therefore, which contained tannins of the catechol series, including the tannins of hemlock, larch, quebracho, mangrove, gambier, and turwar, were condemned, as all these materials produce a leather which on exposure to light and air turns first a red shade of colour and afterwards develops what is now well known by bookbinders and librarians as the red decay, where the leather crumbles off on application of friction. On the other hand, tanning materials of the pyrogallol class, such as sumach, galls, divi-divi, myrobalans, oak, and chesnut, produce a leather which is practically unaffected by light or air. Further, it was found in every case where authentic bindings dating from the 13th century onwards were examined the tanning material used was one of this pyrogallol series. On the other hand, leathers which showed the red decay were in every case found either to have been tanned with tanning materials of the catechol series, or were rotted with acid.
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.
Before drafting his binding specification the librarian would do well to consult the excellent "Note on Bookbinding" by Mr. Douglas Cockerell, published by W. H. Smith and Son, at the price of 1d. Special attention is drawn to the difference of the cost in binding according to Specification I. and II. of the Society of Arts' Committee reproduced on pp. 20-22 of this pamphlet, and to Mr. Cockerell's remarks on pages 9, etc.
The above stipulations should not make any substantial difference in price per volume to those libraries which already have been using high-class leather tanned in sumach, but librarians who have hitherto been content with persians, re-tanned Australians, and other cheap classes of leather must expect to pay a higher price for leather, properly tanned and guaranteed to last. Several large firms of high reputation, who are now catering for the bookbinding trade, have already turned out thousands of skins of a satisfactory nature. These firms are not only anxious to fall in with the requirements of the Society of Arts' Report, but are desirous of removing the distrust which at present exists with regard to leather, and to reinstate this article as being the standard and natural covering for books. For permanent wear, whether for books or other purposes, leather, when properly prepared, is without a rival both for appearance and durability. It is only for the cheaper class of work that leather substitutes are formidable as rivals.
With regard to strengths of various leathers, it is somewhat difficult to lay down a hard-and-fast rule, but in general terms it may be stated that the strongest leather made is pigskin. The fibres are tough, somewhat coarse, but of great strength. The only danger is in the paring down of the skin previous to use in the binding, and therefore, by reason of its thickness, it is well to only use pigskin for the binding of large, heavy volumes where a thick leather can be used without detriment to the appearance of the book. Seal probably comes next in strength. It is tougher than goat skin, and, by reason of the quantity of natural grease which these skins contain, will in most cases remain pliable and wear longer than the average morocco. Seal is closely followed by goat skin. A special feature of goat is the hard grain which it possesses. This is specially to be recommended where much frictional wear is given to the book. Sheep and calf may be put on about the same footing. Both are extremely pliable, but I think one may safely state that books bound in sheepskin leather, if that leather be from the cross breed, Welsh, or other mountain sheep, will probably outlast calf skin. There is no doubt that calf has got into disrepute largely on account of the destructive processes used in the finishing and production of the soft, smooth-grained calf, which has of late years become so popular. Binders must understand that the velvety finish can only be obtained by an undue pulling down of the skin previous to the tanning process or an undue paring on the part of the binder. Both Russia leather and vellum, as binding materials, have done good service in the past, but have lost their old reputation for durability. For the present, librarians are recommended to use these skins as little as possible. A few words suffice to deal with skiver bindings. These are the thin grain of sheep and sometimes calf, and are at their best about equal in strength to thin notepaper, their whole texture and fibrous structure having been split off and their nature destroyed.
It must be understood that the deterioration of leather is not only caused by faulty manufacture or improper treatment in the dye-house or finishing shop. Good bindings of sound leather are frequently destroyed by the neglect of certain elementary precautions on the part of the librarian. The subject is too large to deal with fully in these pages, but librarians would do well to study carefully the detailed report of the Society of Arts' Committee. But the following elementary rules should be observed:--Books should not be exposed to gas fumes, or to the direct rays of the sun; the temperature of the library should not exceed 70° F., the upper strata should be well ventilated, and a thermometer should be hung on the same level as the top shelves in order to advise the librarian whether the temperature is being kept within reasonable limits. Freedom from damp is, of course, an essential condition of library architecture.
The question of leather preservative compositions is dealt with in another chapter, but too much cannot be said against the use of various decoctions which are sold to librarians for coating and preserving leather bindings. Many of these contain turpentine, which has a drying, detrimental effect. Various other emulsions are on the market, but although these give the leather a soft, pleasant feel when applied, this soon dries up, the leather becoming hard and liable to crack. There may be some suitable ingredients for applying to leather bindings, but I am of the opinion that if a library is not allowed to get too hot, and a plentiful supply of pure, dry air is always present, sound leather should require no further preservative.