K. J. Adcock

“ The objection to natural grease in leather can be understood where the latter is intended for colours, but in the case of sole leather it ought not to be a disadvantage, yet, owing merely to the darker appearance of the leather where the grease reaches the grain, its selling value is reduced by 2d. or 3d. per lb. The strange part is that the grain of this sole leather, when made into boots, is buffed on an emery wheel, then sometimes coloured with a paint, and finally sold in boots at the same price as leather free from grease and regular in colour. ”

“ A great point in favour of selling by measurement is that there would be no necessity to weight the leather, and a mere visual examination would suffice to determine the quality, whereas it is often difficult to state whether leather has been treated with injurious artificial matters or not, and certainly impossible to determine the extent of this fraud, without a careful and somewhat elaborate analysis. ”

“ As in many other articles of modern manufacture, quality is sacrificed for appearance. The colour of sole leather is of no importance whatever to the wearer of the boot, and the public should make a strong protest against bleached sole leather, and also against leather weighted with adulterants, if they wish to get boots of good wearing quality. It is difficult to know where the finishing of some of the modern sole leather begins. Formerly, the line of demarcation between tanning and finishing was distinct, for the finishing processes were begun as soon as the hides were sufficiently tanned. ”

“ In fact, it is a tanner's dictum that leather is made or marred in the lime liquor, though this, of course, only applies to a certain extent. Generally, however, the heavier the hides, the longer the liming required. Fortunately, the limited solubility of the lime in water affords a wide margin of safety in working, and the only danger to guard against is the too prolonged use of old liquors, which are readily detected by the strong odour of ammonia. One important property of lime is its lower solubility in hot than in cold water. ”

“ Despite the well-known axiom that the vegetable tannage (but not the mineral) must proceed slowly and gradually in the early stages of the process if the hides are to be properly tanned, the modern tendency is to speed up the tanning, with the result that, in some cases, the so-called sole leather is really not fit for the purpose for which it is intended. The root of the evil is the desperate attempt made by 100 many boot manufacturers to produce lower-priced boots than those of their competitors. ”

“ Public auctions have become so firmly established that it would be impossible for tanners to revert to the old system even if they desired it. The competition of private buyers with the auction markets has certainly benefited the butcher at the expense of the tanner, and the weighing and classification of hides ultimately became so irregular in many markets that the Tanners' Federation of the United Kingdom had to take strong action not long ago to protect their interests. ”

“ There are not many bull hides grown in the United Kingdom, and in many markets they are not classed by weight but simply into best and secondary qualities. Horse hides are of even less value than those of bulls, owing to their weaker texture and irregular substance. That part of the skin under the mane is almost worthless, while the flanks and sides are only useful for a secondary class of boot upper leather, although some fairly good patent sides have lately been produced from horse hide, which is suitable for that purpose owing to its soft grain and pliable texture when tanned. ”

“ On the other hand, the value of hides and skins has risen enormously in the last decade, the period coincident with the rapid growth of the chilled and frozen meat industry, but the increased use of leather in many directions may be mainly responsible for the higher cost of the raw material, although it is obvious that the concentration of the chief supplies of hides in a few lands must tend to increase the severity of the competition among buyers. ”

“ It is true there are tanning drums on the market which are said to obviate all the difficulty found in making sole leather in ordinary drums fitted with shelves or pegs, but a drum that meets the ideal conditions for the production of a solid yet flexible sole leather has not yet been invented. It seems that a kind of inner framework, to which the hides can be attached and which rotates much more slowly than the main drum, may solve the problem. The drum tannage permits the use of an excessive quantity of tannin, which, of course, adds to the weight of the leather. ”

“ The flesh ought to be removed in all cases, for the loose flesh forms very poor and spongy leather. Where hides and skins are tanned and then dried for sale to leather dressers and finishers, there is often the tendency to leave far too much loose flesh on them, with the object of producing as much weight of leather as possible. From the point of view of economy, this is a mistake, for the loose flesh must be removed during the dressing process, whereas, if it had been taken off at first, both material and time would have been saved in the process of tanning. ”

“ There is no danger of foot-and-mouth disease getting beyond the abattoirs or of the slaughter of diseased cattle for food, and both tanners and butchers hope to see the removal of the embargo. So far as possible, each country should raise its own cattle to provide its own meat supply, and this principle is recognised by many countries which prohibit the import of foreign meat: but, owing to the rapid growth of populations in industrial countries, with the consequent increase in the value of land, it has become impracticable to raise enough cattle to supply domestic needs. ”

“ China is another large hide-exporting country; most of the hides from this source are dried in the open air and are generally arsenicated to prevent the ravages of insects. Immense quantities are also provided in all other populous countries, but the demand for leather is generally greater than the production of raw material in those countries. India is a noteworthy exception to this general rule; the production of Indian hides is enormous, and, although the leather trade is being developed, there is a large surplus of raw hides and skins for export. ”

“ So far, only one country, the United States of America, has taken steps to prevent the importation of the disease of anthrax, although most countries have issued regulations in regard to the precaution to be taken to avoid infection by anthrax in those factories where imported hides, wool, hair, and bones are treated. It would seem that the most rational method would be to disinfect the hides before they are shipped, as it certainly appears to be unwise to import any form of disease ”

“ Excepting the bark mill, various kinds of tumblers, the fulling stocks, glazing and rolling machines, there were practically no efficient mechanical aids to lighten the exceedingly laborious operations incidental to leather manufacture two decades ago; but so many improvements have lately been made in the construction of machinery for practically every operation in the trade that most of the machines require very little skill to work them, and can be operated by intelligent youths after a few weeks' experience. ”

“ The principal vegetable tannage used for Indian leather, namely, the bark of the acacia arabica, known to the natives as babul, or babool, has quite a contrary effect, for it contains a large quantity of red colouring matter, which is incorporated with the leather in the tanning process, and although it shows very little in the rough-tanned leather, it is apt to darken if the finished leather is exposed to strong light for a long period. This oxidation is accompanied by a gradual weakening of the fibres of the leather, which is, therefore, quite unsuitable for bookbinding. ”

“ The primary objects of treating raw hides and skins to produce leather is to make them imputrescible and impart various degrees of pliability. These qualities are essential, but the simpler the methods used to attain them, the greater the strength of the leather produced.
The number of materials that will produce leather is legion. Whereas oak bark was almost exclusively used for tanning until the last century, there are now at least twenty useful vegetable tanning materials. The active ingredient of all of these materials is tannin, a colloidal or uncrystallisable substance. ”

“ The dressing and finishing of leathers of all kinds seems to be of growing importance every year, despite the fact that the durability of leather is often impaired by the chemicals and heavy machinery used in order to get a clear and bright colour or a highly-glazed finish. One exception to this rule, however, is japanned and enamelled leathers made by the new collodion-amyl acetate process, which not only produces the so-called "patent" finish, but also adds to the strength of the leather. ”

“ Progress in the art of making leather for gloves has been rapid during the last few years; but further 148 important developments are expected, particularly in the process of tanning. Practically the only method that has been used for many decades for converting kid, lamb, and sheep skins into gloving leather is that known technically as "tawing," which consists of treating skins with alum, salt, egg-yolk, flour, and a vegetable oil. ”

“ The change has been of great benefit to the health of the workers, for the continual stooping over beams and sloping tables, combined with the arduous nature of the work, was very injurious. The reputation that tanning had as a healthy occupation was due more to the work of the labourers than that of the skin workers. (The old-fashioned lime-yards and tan-yards were generally in the open, whereas modern tanneries are roofed.) ”

“ In some countries the methods of preserving hides are actually so bad that the hides have often lost half of their value before the tanner gets them. Two or three of the largest American meat-packing establishments have erected or taken over tanneries to deal with raw hides, one of their by-products. Tanneries have also been erected near some of the large meat works in the Argentine, but the development of the leather trade there is by no means rapid, and at present the United States of America is the largest leather-producing country in the world. ”

“ A third process of making a one-bath liquor combines the use of bichromate of potash and chrome alum, which, when dissolved, is converted into 109 a basic chrome salt by means of a reducing agent. The one-bath liquor can be easily and safely applied to hides and skins, and is used in much the same manner as a vegetable tan liquor, beginning with a weak solution and gradually increasing the strength until the process is completed. The two-bath method needs great care, as a slight difference in the proportions of the ingredients used may alter the character of the leather produced. ”

“ Dressing and dyeing are begun as soon as the leather is satisfactorily aged. The skins are uniformly soaked in warm water, dyed, and re-dressed with egg yolk ("re-egged") , to which a small quantity of olive oil, or a sulphonated oil, is added. Some dressers prefer to give the second tawing mixture before dyeing, but the advantage of dressing the leather after dyeing is that the colour is securely fixed. In "re-egging," many dressers use a similar mixture to the first dressing. The dyeing process is of great importance, since the colour must be fast. ”

“ Many are inclined to believe that both changes take place, and this view is probably correct, as a pure tannic acid produces a thin, empty leather, while a tanning material which contains a fair proportion of non-tannin matters, yields a full and firm leather. The practical tanner who adapts his work to the theory that tanning is a process of feeding the hides with gradually increasing strengths of tannin, is, in any event, on the right track. The suspender liquors are always weak in tannin, and are pumped from "handler" liquors through which packs of hides have already passed. ”

“ A patent has lately been granted to an American inventor for the production of a strong and cheap belting. Flesh splits of hides are simply stuck together with a collodion or nitrocellulose solution. Any number of layers may be used, according to the substance required, the only essential quality being that the leather should be free from grease. The adhesive property of nitrocellulose solutions is probably stronger than that of any other material, but, unfortunately, the tough film they form on drying does not grip a greasy surface. ”

“ There are other methods of producing leather which are not used on a large scale, but sufficient examples have been given to show that an exact definition of leather cannot be summed up in one or two words. ”

“ Whether or not the concentration of these huge meat works into two or three centres is likely to benefit the leather trade is a debatable point. The flaying, trimming, and curing of hides in these establishments are certainly superior to the work done by the average butcher, while, owing to the large numbers of cattle slaughtered, the hides can be closely selected. ”

“ It is still a debatable point among tanners as to whether it is better to buy hides direct from the butcher or through these markets. It is certainly a great advantage to put hides into work quickly (although not before they are quite cool) , as time is saved in the soaking process, and there is practically no loss of gelatinous matter. On the other hand, the tanner is able to buy just the selection of hides that he wants from the auction markets. ”

“ If this tendency to fermentation and oxidation of the colouring matter could be checked completely, divi-divi would be a valuable material, as it makes a firm leather of good colour. When dried, the pods curl up in the shape of the letters S and C. The tannin is found in the husks of the pod. The seeds, which contain no tannin, are so hard that it has not yet been found profitable to extract the oil from them. Very similar tanning materials to divi-divi are cascalote, indigenous to Mexico, and algarobilla (caesalpinia brevifolia) which grows in Chili. ”