Leather Made

To Fit Your so called because of the use of the beam, a convex sloping slab of w^ood upon which a hide or skin is placed while the operator removes hair or Needs flesh with a knife. Second is the actual tanning operation. The third step is the C. W. Beehe finishing operation. Changes at any stage make a difíerence in the finished leathers. The best tanning process is the one in which the methods used in Leather is made by treating skins any ste]:> harmonize with those used in and hides so that they will not be acted other steps to give the desired final upon by bacterial enzymes, will not be e fleet. gelatinized by warm water, and will not become brittle when dried out. TANNERS usually receive hides and This treatment, known as tanning, skins dry or cured; that is, enough gives them the desired softness, flexi- water has been removed, usually by bility, and firmness. salting, to prevent spoiling. Usually the Hiiavy k^ather is used w4iere thick- hair is still on the hides and must be ness, firnmess, and solidity are needed, ríMTioved before tannage. As tfie wool as in shoe soles, machine belting, and on sheepskins is more valuable than the harness. For it, thick heavy hides from skins, it is generally removed by the cows or other large animals are needed. growíT or the wool puller, and the skins Light leather is used where flexibility Tciwh. the tanner in a pickled condi- and softness are desired, as in shoe up- tion—that is, preserved with a solution joers, gloves, upholstery, garments, lug- of sulfuric acid and salt. gage, or chamois. It is usually made The first step in the preparation of from the skins of small animals or hides or skins for tanning is soaking in young animals of larger species, such water to clean off accumulated dirt, to as goats, sheep, calves, or colts. It may remove excess salt, and to restore some also be made by splitting the hides of of the water lost in drying. large animals into layers. Fur skins are I'he second st(^p is to soak them in a type of light leather in which the pro- a lime solution, usually containing duction of leather from the skin, while sodium sulfide, to loosen the hair and important, is secondary to the preser- epidermis, which are then removed, vation and improvement of the fur. commonly by unhairing machines. The Leather is of two general classes, adhering connective tissue, or flesh, is heavy and light. Each requires its own then removed, and the hides or skins type of tanning. The tanning of heavy are scudded. Scudding means scraping leather used to take years; indeed, in by a blunt blade, which removes the many parts of the w^orld today it still remnants of the glands, hair roots, lime requires a whole year. Even in modern soaps, and dirt. Some of the lime is practice the tannage may last 2 to 3 then removed by washing with water months. Light leather is tanned quite or with acids or deliming agents to re- rapidly ; often only 2 days are required. move more of it. Leather is made in three stages. First, The tanner changes these operations the hides or skins are prepared for to get the kind of k^ather he wants. tanning—the bcamhouse operations^ If he makes hard, firm sole leather. 002722^—ni- -40 704 1950-19 5 1 YEARBOOK OF AGRICULTURE he tries to prevent loss of hide sub- made from barks, woods, leaves, or stance and to get a firm, plumped hide. pods of natural vegetable origin. Most He soaks and limes for only a short upper leathers arc chrome-tanned— time; he uses lime liquors which arc that is, tanned with chromium salts of sharp (alkaline) and not too mellow mineral origin. and which contain enough sodium sul- Heavy leather is usually tanned in fidc for rapid unhairing. He delimes solutions of vegetable tannins by a by merely washing some of the lime countiTcurrent system. The limed, un- from the hides wn'th water. haired, and partly delimed hides come The tanner of soft, flexible, light into contact first with a w^eak, non- leather soaks and limes for a long time. astringent (mellow) liquor, which has He gets a mild action by the use of a already been used for the tannage of mellow' lime liquor made by using the more thoroughly tanned hides. After same liquor for several packs of skins. a day, the liquor is replaced by one of He can also get a mild action by us- slightly higher tannin content and ing arsenic sulfide inst(\id of sodium gre¿iter astringency. The pro(x?ss is re- sulfidc. peated for several weeks, each liquor A tanner must be on the alert to being stronger and more astringent change his methods according to the than the preceding one. The liquor kind of hides or skins he gets. These from the final tannage goes on less come to him from many sources and tanned leather and so on until finally, may be hard as flint or soft and flexible. when it has become w^eak and mellow, No matter in w'hat condition he gets it is used for the first tannage. Thus the them, he must know^ w^hat to do so that leather and the liquor proceed in oppo- they will be as nearly ahke as possible site directions through the tanyard. on leaving the beamhouse to be tanned. This countercurrent system is necessary After the beamhouse treatment, because if hides W'Crc put into strong skins for soft, flexible leather need to liquors they would be (^ase-hardened— be thoroughly delimed and made flat tanned hard on the outside and left and flabby. The tanner does that by raw inside. bating. Bates formerly consisted of The system allows an almost infinite suspensions of dog or bird dung; now variation to produce dififerent types of they are commercial preparations^ usu- leather—the tanner can make his ally a mixture of pancreatic enzymes leather more firm or more flexible or and ammonium chloride. The tanner lighter or darker by his choice of tan- may change the concentration, time, ning materials. He can shorten the time and temperature to suit his needs. of process or lower the cost by the Some skins after bating are pickled— proper blend of different materials. treated with a solution of sulfuric acid Tanners formerly made their liquors and salt. The acid brings the skin to the directly from the bark. Now most of necessary condition for tannage. The them use a strong liquid extract, or a salt prevents the excessive swelling that solid or powdered extract, made by a would otherwise be caused by the acid. manufacturer of tanning materials. The efTects of the pickling may be In the early days, tanning methods changed by concentration, tempera- W'Crc based on the use of oak bark and ture, and time of the process. later hemlock bark. But w'hen oak and The hides or skins are now ready for hemlock became scarce, tanners had to tannage. If you look at an ordinary change their methods to fit new ma- shoe you can sec the difli'erencc betw^een terials. The most widely used tanning the two types of leather. The upper extract is quebracho, from southern is a typical light leather and the sole is South America. A blend of quebracho a typical heavy leather—or at least the extract with chestnut extract, our most tanner hopes so. Most sole leather is widely used domestic material, forms tanned with vegetable tanning extract the basis of n:iost American tannages. LEATHER MADE TO FIT YOUR NEEDS 705 Quebracho extract, used in the usual With that wide variety from which sulfited foriTij penetrates rapidly into to choose, the tanner has been able to the hide to give a leather that has change his blend of tanning materials good color and feel but tends to be flat almost at will to produce the desired and poorly filled. Chestnut extract effect. However, the trees which pro- gives a firm, well-filled leather, but it vided these materials arc getting scarce, penetrates slowly if it is used alone and and although steps are being taken to tends to make the leather too firm and develop new tanning materials, either brittle. The tanner blends the materials natural or synthetic, it is certain that to modify the firmness or flexibility of in the future the tanner will not have the leather as he desires. the wide choice he has had in the past. Tanning blends usually also contain Instead of changing his tanning blend other kinds of tanning extracts, which to modify the leather, he must now aid in acid formation, increase pene- treat the available tanning extracts be- tration, improve the color and general fore use, or modify the tanning proc- appearance, or lower cost. Myrobalans ess, so that one tanning material may extract, made from the unripe nuts of give effects formerly produced by a the myrobalans tree of India, for different type of extract. example, is used to produce acid. To modify the properties of the fim- Wattle extract, from the bark of the ished leather, the tanner may also mimosa tree, now grown in South change the tannin content of the liq- Africa, may be used to replace some of uors at various stages of tanning. These the chestnut or quebracho extract liquors, with an average tannin con- whi^n high prices make that desirable. tent of 0.5 percent in the Aveakest and 9 Sumac, most of which is now imported percent in the strongest, may be made from Sicily but which grows wild in either stronger or weaker. Another fac- this country, is used to improve the tor is the purity of the liquors—the color and feel of the leather. In all, ratio of tannin to total soluble matter. several hundred different materials— A low purity makes soft and spongy woods, barks, pods, leaves, and roots— leather; a high purity is required for contain enough tannin to justify their firm leathers. The acidity, measured use in tanning. But not very many of either as total acid or as pH (active them arc available to tanners in extract acidity), also modifies the character of form, although enough ha\T always the leather. The hides carry lime over been available to give wide selection. into the tanyard and it must be neu- Sometimes used in tanning blends is tralized and th(î hides brought to the the so-called sulfite-cellulose extract, slightly acid condition necessary for which is a solubilized lignin byproduct tarming. Gen(.Taliy, enough acid is of the; sulfite paper industry. Its tanning formed by the fermentation of the valuéis doubtful, but it lowers costs and sugais present in tanning materials, probably has some value in m^odifying but sometimes it is necessary to add a the character of the blend. There are weak organic acid, such as lactic or also available a number of syntans. acetic acid. An acid condition of the These are usually made from phenols liquors is required to plump the hides and aldehydes in the same way as baké- to the swollen condition that gives firm- lite or other synthc^tic rc^sins, except ness and fullness to the finished leather. that they have been made soluble in Too much acid, however, may cause an water by treatment with sulfuric acid overswclling of the hide and produce or other reagents. They are not true tender leather; it may even cause case- synthetic tannins, but in some cases hardening. The best acid conditions are give results similar to those of natural probably between pH 3.5 in the tannins, for which they may be sub- stronger liquors and pH 4.5, or perhaps stituted if their som.ewhat higher cost slightly higher, in the weaker liquors. will j3ermit. Mineral salts or inorganic material 706 1950-1951 YEARBOOK OF AGRICULTURE are also in tanning liquors. If they arc tions. Leathers must be lubricated with salts of the weak acids, they lower the oil or grease. For sole kíather a mix- acidity of the liquor and reduce its ture of animal or fish oil, such as cod, plumping power. Ahnost all other with mineral oil and sulfonatcd oil is types of mineral matter, w^hilc not af- commonly used. For harness leather fecting the acidity, reduce the plump- a mixture of greases, such as tallow, ing power. In either case, flat, poorly and oils, is used. To give the leather filled leather is made. The mineral greater grease-holding capacity it is not matter comes into the tan liquors from tanned so heavily as sole leather is. I'hc the lime brought in by the hides, from leather may be rolled to make it hard the mineral constituents of the tanning and firm, staked to make it flat and material, or from the water used. The flexible, and brushed to polish it. Sole countercurrent system already de- leather may be bleached to gi\'e it a scribed gives the tanner an opportun- light(?r color. Loading materials, such ity to regulate the amount of mineral as epsom salts, glucose, and svilfite-cel- matter accumulating m the liquor. A lulose extracts, may be added to make faster flow^ of the liquors through the it retain its thickness and firmness in tanyard reduces this amount, but it the finishing operation. Finally, the also retards the mellowing of the leather must hv. dried—an important liquor and cuts down the amount of step that takes careful watching. The acids formed by fermentation. One tanner may modify any of these proce- factor must be balanced against the dures to get the kind of leather he other to determine the proper proce- wishes. dure. The tanning of light leather is a short The tanner may also modify the tan- process as compared to heavy-leather ning processes. At first the hides are tannage. It starts in the beamhouse, suspended in weak liquor in vats in already described. the so-called rocker section and given . For some kinds of light leather the a slight rocking motion. The hides stay tanner uses vegetable tanning ma- in the rocker section until the tannin terials, syntans, or mixtures of them. has penetrated them. The customary The skins may be tanned somewhat as way of finishing the tanning has been in the early stages of heavy-leather to place the hides flat in vats, laying tannage or they may be tanned by tum- one over the other, sometimes sepa- bling in a drum with a solution of the rated by a thin layer of bark. They re- tanning extract. Sometimes finely mained in these lay-away vats, in which ground sumac leaves and water arc the liquors were strengthened one or added to the pickled skins in a tanning more times, for several weeks or drum and thti .skins are tanned by the months, until they were thoroughly tannin leached from the leaves while tanned. Tanners have found that by in- tumbling. creasing the time in the rockers, using Some tanners, especially tanners of stronger liquors, the time in the lay- glove leather, use an alum tannage. avv'ays may be shortened, or these vats They tumble the skins in a drum con- eliminated. This greatly shortens the taining a solution of aluminum sulfate, time of tanning. Another w^ay to made alkaline with sodium carbonate shorten it is to tan in revolving drums and containing salt to prevent swelling. with strong liquors toward the end of Toward the end of the process the the tannage. Some tanners believe that liquor is neutralized with enough borax shortening the time by these methods is or sodium bicarbonate to precipitate accomplished at the expense of some the alum thoroughly in the skins. A of the firmness and fullness desired in mixture of egg yolk^ oil, and flour is the final heather. rubbed well into the leather, which is The tanner can modify the character then allowed to dry and age for several of the leather in the finishing opera- weeks before beino* washed and fin- LEATHER MADE TO FIT YOUR NEEDS 707 ished. Alum tannage is also used for own methods of preparing tanning furs. In that case, the alkaline alumi- liquors and adjusting the strength, num sulfate is generally made into a acidity, and ratio of liquor to leather. paste with flour and oil and rubbed He determines the time of tanning, into the flesh side of the skin. the temperature, the mechanical Some tough, white leathers are methods, the degree .and manner of tanned with formaldehyde. Formalde- neutralization, and the amount and hyde, however, is used more as a type of neutral salts to give him the pictannage than as a single tanning efí'ect on the leather that he wants. agent. It either imparts new character- The finishing operations, particu- istics to the finished leather or it aids larly staking, have a greater effect on in tannage with the other material. light leathers than on heavy leathers. The skins are tanned with dilute solu- AÎost leathers, left to dry by themselves, tion of alkaline formaldehyde, which become hard and brittle because of combines with the skin substance to adhesion of the fibers, but if they arc form a type of leather. The alkalinity flexed repeatedly at the proper stage must be carefully regulated. The of drying the fibers become separated liquors will not tan unless sufficiently and do not adhere when dry. When the alkaline, but if they are too alkaline the Indians tanned deerskins for buckskin leather will be brittle. leathers, the squaws did the job by Chamois leather is oil-tanned. Al- chewing on the leathers. Staking for- though originally made from the skin merly was conducted by hand over a of the chamois goat, it is now usually rounded blade fixed vertically. Some- made from the inner layer of sheep- times the operator used his bare knee skins. By alternately impregnating the instead of the blade ; the process is still skin with cod oil or some other suitable largely used for glove leather but for oil and drying, the oil combines with other leathers has been replaced by the skin to give chamois leather. machines. The chrome-tanning process is used Tanners may combine difl'erent for most light leathers, especially shoe kinds of tannage to make the kind of uppers. Chromic oxide formed from leather they want. For example, heavy sodium, dichromate combines with the leathers may be chrome-tanned and skin to form this type of leather. The finished with a vegetable tannage. The skins may be impregnated with an acid time of tannage is thus shortened and sodium dichromate solution by tum- the leather retains the properties of a bling in a revolving drum, and then vegetable tannage and acquires new with chromic oxide formed directly in properties, such as resistance to moist the leathcT by tumbling in a sodium heat. Some fight leathers are pretanned thiosulfatc solution in a similar drum. with formaldehyde before retannagc In most cases, however, the sodium with chrome, alum, or oil to give dichromate is reduced to chromic acid greater flexibility and resistance. before being used and a tanning liquor R. W. Frey and C. W. Beerbe found is made fromi the acid. Bated, skins from that a combination chrome- and vege- the bcamhouse are pickled in acid and table-tanned bookbinding leather has salt and drummed until tanned. They the resistance to acid deterioration of are then neutralized with a mild alkali, chrome leather combined with the washed, and finished. workability and good appearance of Several other methods for tanning vegetable-tanned leathers and that light leather are used to a limited ex- the vegetable-tanned leathers retanned tent. Inhere are so many ways of tan- with alum showed the same effect. ning light leather that -it is probable C. W. Beebe, J. S. Rogers, and VV. F. that no two tanneries o])erate in liappich discovered that retanning exactly the same way. Every tanner has vegetable-tanned insole leather with his own bcamhouse procedures and his alum solution, suitably stabilized, im- 7o8 1950-1951 YEARBOOK OF AGRICULTURE parts resistance to moist heat and to don, G. W. Beebe, and J. S. Rogers deterioration by molds. In pn^liminary have devised methods for fermentation tests they found that the serviceability of the sugars present to increase the of such vegetable-tanned leather may purity of the extract. Tanners gener- be giTatly increased by alum rc^tannage. ally want high-purity extracts for the Tanners now have the benefit of re- production of firm leathers. search results in changing their tan- Some of the new syntans (developed ning processes to give them the leathers by H. G. Turley and J. il. Highberiri^r, they wish. G. D. McLaughlin and E. A. H. Bump and F. O'Flaherty, A.^^FI. R. Theis, in The Chemistry of Leather Win he i m and E. E. Doherty) appear Manufacture, give the results of in- promising. Sulfonyl chloride has been vestigations which showed that sodium proposf^d by M. F. White, W'. T. sulfhydrate, instead of sodium sulfide. Roddy, and O'Flaherty as a substitute or methylamine may be used as an un- for cod oil in making chamois leather. hairing agent in the bearahouse. New E. R. Theis and T. Kleppinger have sources of tanning materials are being found that stabiHzing or "masking" developed, but it is probable that the salts have been found capable of im- choice of such materials may be re- proving chrome leather. Stabilizing stricted. Therefore, it is of interest to salts of the same type have aided in the investigate methods of modifying exist- alum retannage of heavy VTgetabli^ ing tanning materials. Sulftting que- tanned leathers by increasing the pene- bracho to increase its solubility and tration of the aluminum salts. ease of penetration into the leather is now an accepted practice. G. W. BEERE is a graduate of the P. Ghambard reported that during University of California. After 11 years the w^ar French tanners modificad ch(^st- as chemist with a firm of tanners, he nut extract by increasing the solubility joined the Department of Agriculture and pH to give it some of the properties in 1929. He is now head of the tanning of quebracho extract, which was materials and processes section in the almost unobtainable. In the develop- Biireau of Agricultural and Industrial ment of canaigre extract^ T. G. Cor- Chemistry,

ToRAcco STEMS and leaf wastes from factories that process tobacco are highly regarded as fertilizer for many crops. They are evaluated commercially on the basis of the nitrogen content as organic nitrogen and the potash on the basis of carbonate of potash. One ton of air-dried stems is usually considered equal to 3 to 4 tons of fresh stable manure. The nitrogen content ranges from 2 to 4 percent and the potash from 3 to 8 percent, depending on the type of tobacco. Tobacco st(^ms arc recommended for use on roses and nearly all orna- mentals, lawms and hay crops, citrus and small fruits, most truck crops, and the home garden. They have been used to grow spaw^n for mushroom culture. They should not be used, however, for tobacco or other solanaccous crops unless they are sterilized, because they may carry some of the virus diseases common to those crops. They can be used in nearly every place where barnyard manure is recommended.—Ernest G. Beinhart, Eastern Regional Research Laboratory.