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INDEX 55

THE ROGER LEVENSON MEMORIAL FUND

History of Sumach Tanning in England, Degradation of the Manufacture of Leather, and History of the Reform Movement.

E. WYNDHAM HULME.

The section of the leather trade to which this Handbook relates is that concerned in the manufacture of light leathers tanned with a pale tannage preparatory to being dyed. Bark and most other vegetable tanning substances leave a colour on the skin which cannot be removed without detriment to the durability of the leather; the retention of the colour, however, detracts from the purity of the final colour imparted by the dye. The reputation in the past of the sumach-tanned Spanish leather was founded upon this peculiar property of sumach of leaving the skin white, and on this point the wisdom of the ancients has been justified by the results of an exhaustive series of experiments conducted by the Society of Arts' Committee, which have given to sumach the first place in the list of tannages for light leathers.

Passing from the domain of chemistry to that of mechanics, the Committee of the Society of Arts has emphasized the need of a return to sounder and less ruinous methods of dealing with leather; but their recommendations are so clearly set out in their Report that it is proposed here to touch upon one point only, viz., the artificial graining of leather. The Committee remark that, whereas many examples of sound sheepskin, dating from the 15th century to the early part of the 19th century, had been brought to their notice, "since about 1860 sheepskin as sheepskin is hardly to be found." Now, the decoration of leather by the impression of patterns by mechanical pressure had long been known, the lozenge pattern of early russia leather having been effected in the 18th century by means of engraved steel cylinders. But in 1851 it occurred to an ingenious mechanic that, by means of the electroplate process, an exact reproduction of the grain of the higher-priced skins might be communicated to sheepskin or other inferior leather whereby the selling value of the latter would be considerably enhanced . From this date, therefore, sheepskin disappears from view only to reappear as imitation morocco, pigskin, or other higher-priced leather. So perfectly does the counterfeit skin imitate the original on the bound volume that the two can only be distinguished with certainty by microscopic examination. Librarians, therefore, must bear in mind that a familiarity with the natural characteristics of the ordinary binding leathers is no safe guide to the character of the leather of a binding. The utmost that can be said is that the leather is either genuine or else a remarkably good counterfeit, a conclusion which, it is hardly necessary to say, is not one of great value in practice.

As might have been supposed, the rapid decay of leather bindings in the 19th century, resulting from a combination of the above malpractices, with the attendant evils of heavy outlay upon rebinding, cropped margins, and ill-matched sets upon the shelves, from time to time attracted the attention of booklovers and bookbinders; but their efforts to determine the causes of the deterioration and to find a remedy have until recently met with very little success. In 1842 the subject was investigated by Professors Faraday, Brande, and others on behalf of the Athenaeum Club. This committee is largely responsible for the "sulphur in gas" theory--a theory which was never wholly true, even at a period when the percentage of sulphur in coal gas was much higher than at present , and which now has ceased to have any practical bearing upon the matter. It should be noted that, in 1851, Crace Calvert, the well-known Manchester chemist, came to a different conclusion. After pointing out that decay in leather was observable in libraries, such as the Chetham Library, in which gas had never been used, he stated that the presence of sulphuric acid in leather bindings was attributable to one or more of three causes: to the pollution of the atmosphere by consumption of coal in the Manchester factories; to the action of gas fumes in unventilated rooms; to the use of sulphuric acid by the tanners; and he further expressed his opinion that the seat of the disease would be found in irregularities in the processes of tanning--in other words, that the disease was aggravated rather than originated by these first two causes . Calvert's views, however, met with very little support. In 1877, at the Conference of Librarians in London, a proposal was made that a committee of librarians and chemists should deal with the matter, but no effect was given to the proposal. Ten years later a series of experiments on the action of gas fumes and heat was undertaken on behalf of the Birmingham Library by Mr. C. T. Woodward . Strips of leather exposed for 1,000 hours to the action of gas fumes, at temperatures of 130? and 140? Fahrenheit, showed a mean absorption of sulphuric acid of 1?78 per cent., accompanied by a marked reduction in their stretching capacity and breaking strain. The experiments on the action of heat alone were regarded as inconclusive. Mr. Woodward suggested that the Library Association should undertake the testing of leathers, and that librarians should thereafter employ only leather of a given standard; but once more nothing was done. In the meantime the reputation of leather as a binding material continued to dwindle; one leather after another was tried, found wanting, and excluded from library practice, while various leather substitutes--buckram, art linen, and imitation leathers, gradually took its place. It is due to the efforts of Dr. Parker and Prof. Procter between 1898 and 1900 that the real facts of the case have been brought to light. In the latter years an agitation in favour of standard leather was set on foot by Lord Cobham, Mr. Cockerell, Mr. Davenport, and others, which resulted in the appointment by the Society of Arts of a Committee on Leathers for Bookbinding, the cost of which was met by a grant from the Leathersellers' Company.

Upon the publication of the first report of the above Committee in 1901 the subject was taken up by the Council of the Library Association, and after several papers had been read at the monthly meetings in London and elsewhere, a Committee was appointed to ascertain how far Members of the Association were prepared to accept a common standard for binding leathers. For this purpose in March 1904, close upon 1,000 circulars were addressed to the libraries of the United Kingdom asking for a statement of their views upon the following proposals, amongst others, viz.: that the Council should appoint an official analyst; that they should publish a handbook giving to members of the Association such information as would enable them to secure sound leather at a reasonable price. The circular meeting with a favourable reception, the Council invited Dr. Parker to draw up a scale of fees for the analysis of leathers, and the scale having been duly approved, Dr. Parker was at once appointed analyst to the Association.

Since the appointment of the Committee abundant evidence has been forthcoming that at last the reform of light leathers for bookbinding and upholstery is now in sight. The efforts of the Committee have been warmly seconded by the Press. In the recently concluded Government binding contracts a clause has been inserted enabling any department to obtain standard leather and rendering the contractor liable to heavy penalties for infringement of the conditions of this clause; yet the price paid for bindings in this leather is only fractionally increased. From the outset the Committee have been assured of the support of the leading firms of leather manufacturers, who have recognised that, if leather is to regain the ground which has been lost, it must be by the adoption of a common standard of manufacture and by the introduction of honest trade descriptions in the retail trade.

Hence where the provenance of the leather is declared and the method of its manufacture supported by a written guarantee from the leather manufacturer, the need for periodical analysis of samples is less urgent. But where the bookbinder is unwilling or unable to state the provenance of his leathers recourse to chemical analysis is the only safeguard. The librarian on his side will materially assist the binder by limiting his demand to leathers of a few standard shades and by abstaining from insisting upon accurate matching to pattern. If the piecing, panelling and lettering of serials is kept uniform, a want of uniformity in the shade of leather is not of much practical moment. In the meantime the librarian should keep a vigilant watch for the following symptoms of deterioration:--

General shabbiness and tenderness of leather, especially at parts where the leather is strained over the cords on the back or edges of the boards. Probable cause: Sulphuric acid.

Red rot in morocco. On friction the leather turns to a red powder. Probable cause: A Persian or East Indian half-bred sheepskin has been supplied in place of goat.

Withering of pigskin accompanied by discoloration. Probable cause: Over "pulling down" of the skin in the "puering" process. If the pigskin has been dyed in a bright shade, acid also is present.

Deterioration and discoloration of smooth and light-coloured calfskins, especially law calf. Probable cause: Use of oxalic acid by the bookbinder to remove grease marks, &c.

The Causes of Decay in Bookbinding Leathers.

J. GORDON PARKER.

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:--

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 o

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