TANNING is the art of preparing raw hides or skins for the hand of the currier; or for immediate use, without any further operation.

The first part of this definition includes all leather used for the upper part of shoes, coashes, coach-harness, saddler-leather, &c. and the last, the manufacture of bin or backs, &c.

We shall first give a general account of the process of mar- manufacturing leather comprehended under the first part of the definition; and then explain separately the particular operations comprehended under the general process.

When the hide or skin is received raw from the hand of the butcher, it is thrown into a water-dub or other piece of water, to cleanse it from the blood and gore; after which, the horns and tail are cut off; then it is put into the lime, and wrought there according to the directions given below; from thence it is wrought into the bait, and cleansed therefrom the lime, &c. It is next transferred to the ooze; and when properly filled, according to the directions on that head, it is conveyed to the tann-pit, where it is tanned; which finishes the process.

Before we proceed, it will be necessary to give a short view of the nature and structure of leather, which will contribute to explain the reason of the different operations it passes through.

All hides or skins, when received from the hand of the butcher, are a bundle of connected tubes, somewhat resembling a honey-comb fixed on a basis; on the flesh-side, of an extreme close texture; but all open on the hair or grain side. These tubes contain a fatty or mucilaginous kind of matter; which, if allowed to remain in a fluid state, would corrupt the leather, and, if dried in the hide, would not only occasion a crisp or hardness in the leather, and be easily softened by moisture; but would also, in the course of tanning, in a great measure oppose every substance that can be applied to consolidate and preserve the hide from corruption.

To extract this matter; to swell and expand the pores as much as they can bear, without a diffusion of parts, in order to increase the thickness, and the more easily to re-fill or introduce a matter less subject to changes from drought and moisture; to preserve the fibres that compose the leather from putrefaction; and to consolidate the whole into one durable mass; are the ends proposed by the several operations of tanning.

Of Liming.

The extraction of the matter contained in the pores being the first aim of the tanner, the first step is to open and expand the fibres, that the matter may be the more easily ejected, in order to give room for the subsequent reception of the tan. This is done by common flaked lime infused in water, and is made up in a pit built with stone, of a length sufficient to contain a middling hide, but seldom so broad as to allow it to lie at its full breadth. The hides are generally treated in the lime in the following manner. They are thrown into a lime-dub, of a weak or slack consistence at first; where they are drawn out and thrown in twice or thrice every day, for a few days. They are then conveyed to a lime of a stronger quality, and drawn as before, though perhaps not so often; once in a day, or once in two days when they are further advanced, may suffice. After they have lain there for ten or fourteen days, the strength of the lime may be increased, or they may be carried to one of a stronger nature, where they are drawn and returned as before till they be completely limed.

As the halting and retarding the operation in particular cases may be necessary; and as it is material for the quality of the leather, that the lime should make an equal impression upon the hide; or rather, if possible, that the weaker parts should be saved, and the stronger more exposed; the following observation may be of use. In most yards there are from 20 to 40 hides or upwards wrought in a lime at a time. When these hides are all thrown in, they must necessarily be made to lie spread out upon one another, as close as possible, to take up little room. By this means those that are near the bottom of the pit will be squeezed so closely together by the pressure of the superior hides, that the water, the medium by which the lime is communicated to them, will be almost entirely excluded from acting upon the body of the hide, while the bellies and other outer skirts will be exposed to its full force. For this reason, it is necessary to change their position often, that the different parts of the hides may have nearly the same opportunity of being impregnated with the lime: and in this view, since drawing in the limes is necessary, it is also evident, that no prejudice can accrue to the leather from the frequent repetition of it, but may be greatly hurt if it is neglected. The often drawing of leather must not only bring on the operation more equally, but must at the same time quicken the effect of the lime, as the exposure of the hide to the air and lime by turns will give it an opportunity of acting with greater force. Besides, the workman has it in his power, every time the dub is drawn, either to add new strength to it (if necessary) by giving more lime, or to make it exert the strength it already possesses by stirring or raising the lime from the bottom. Thus the workman has it greatly in his power to accelerate or retard the operation as he shall think proper. Small leather ought to be drawn oftener than large, as it is not so able to resist the strength of the lime. During very hot weather the lime will operate more quickly than in cold: therefore the workman ought to pay strict attention to the state of his limes at that time, and draw oftener. The rays of the sun, if allowed to act any time on the leather when it is in the draught, will greatly hurt it.

From the above hints, the workman will be enabled to form some judgment how to vary his work according to the different circumstances that may occur. And here it would seem requisite, that some directions should be given for knowing when the leather is sufficiently limed. But it is impossible to convey ideas in an intelligible manner by words, which can only be acquired by practice and frequent observation. Only we may observe in general, as the hide becomes limed, it leaves the original raw fleecy appearance, has more of the appearance of being boiled, and becomes more plump and spungy. But all these appearances are the more visible in proportion as the leather is over-done; and therefore it would be extremely dangerous for a person without experience to trust to the above marks. However, though the time taken to perform this operation may be much varied; yet the ordinary time for a middling hide is from 4 to 6 weeks, and so in proportion for larger and smaller leather.

Of Baiting, and other work before Oozing.

The hide is now stript of its hair, and all the slimy fatty stuff separated from the leather that is found adhering to the flesh-side; the first of which operations is called hairing, and the last fleshing. After which, as it is the workman's aim to discharge the matter contained in the pores of the leather, as also the particles of lime that may have infu- to be ejected into a greater state of fluidity before we attempt to repel it. An infusion of hen or pigeon dung and water, (which is called a bait,) has been found to be the most effectual thing for answering the above end. Into this infusion the hides are thrown promiscuously, where they are drawn in the same manner as directed in the article of liming; and in proportion to the draughts given, the strength of the leather, trim of the bait, &c., the workman will find his point gained from 4 to 8 days: he will find the leather reduced to a soft mellow consistence without any corruption or decay of parts, the matter more fluid and less tenacious, and easily separable from the hide upon working it on the beam with the tanners knife: but as once working cannot purify the hide, the workman must soak it in water, and work it on the beam, alternately, such a number of times as his judgment shall direct, in order to purge it thoroughly; and as it was observed before, that all the pores of the leather were open on the grain-side, most of the work should be applied on that side. As a putrefaction or corruption of the parts, or an extension of the fibres beyond their proper tone, can never be remedied when once begun, the over-doing or undue management either in baiting or liming, must be equally fatal. To obtain the ends proposed by these two operations, and at the same time to guard against their bad effects, require more experience and knowledge in the nature of leather than any other operation it has afterwards to go through.

Of Oozing.

The hide, when ready for the ooze, ought to be nothing but a bundle of empty tubes void of all fluid matter; that is, composed of nothing but what is called the solids of the hide, without any decay or corruption.

It is now the tanner's business to fill these tubes or pores with a more durable matter, in order to support the fabric of the leather; which is the end of oozing. A number of different substances have been tried for this purpose; but none are equal to oak-bark. This bark, after it is thoroughly dried, is pounded, or rather bruised with a mill or other instrument; the powder is sifted out for the purpose of making up oozes, which is only an infusion of this powder in common water; an old or exhausted ooze (if not begun to corrupt) may be renewed by adding more bark, according to the strength of the ooze required. This liquor is deposited in a number of handlers or dusters, (as they are called,) as occasion requires, and the hides are thrown promiscuously into it, where they must be drawn and returned much in the same manner as directed in the article of liming, and carried from a weaker to a stronger ooze as the leather shall require, till they are found to be sufficiently filled. It will be found, that the finer particles of the bark will infuse themselves into the pores of the leather, and lodge there; and at the same time the astringent quality will strengthen and brace the fibres, and bring them again to their proper tone, after their relaxed state in the bait, which will make the leather appear to swell, and feel plump and soft. Here again no rule can direct an unexperienced person to know when a hide is properly oozed; and indeed some kinds of leather require a greater and some a lesser degree of it, according to the purpose for which it is intended; but in general, there is less danger in oozing plentifully than in being sparing of it, as it always adds to the weight and beauty of the leather. A middling hide may be oozed in three weeks, and sooner or later in proportion to the strength of the ooze, the number of draughts, and heat of the weather.

Of Lopping, or what is more properly called Tanning.

This part of the operation is designed to preserve the fibres from corruption, and at the same time to consolidate the whole into one compact body; or, in some sense, it may be called lignifying the hide, (if the term may be allowed.) This must evidently be the work of time, as the nature of the fibres must be in a great measure changed, and the new-imbibed matter incorporated and consolidated with them. In order to perform this, the hides are spread out at their full breadth and length in a vat, and a stratum of beat bark thrown betwixt each of them. This vat holds at first as much liquor as will just cover the hides; and in this situation they are allowed to lie till the strength of the bark is thought to be exhausted, which is commonly from four to six weeks; and the operation is repeated till the hides are sufficiently tanned, and which is generally from two to four times, according to the strength of the leather. The bark should be rounder beat, and more given to the lop, for large hides than small ones; and consequently larger leather should lie longer in the lop.

Of Currying.

The leather, when only tanned, is not sufficiently soft and pliable to answer a number of purposes. The currier's province is to reduce the leather to the proper thickness, pliability, and colour, requisite for the different uses to which it is applied; and though there is a material difference in the method of manufacturing the several kinds, and a good deal of dexterity required; yet what could be here said of them would be of little use to those who are unacquainted with the business. We shall therefore reduce all we are to say on this subject to a general detail of the process.

The leather, after it has dripped some time from the tan-pit, is shaven on an upright beam with a knife whose edge is turned on the one side, and with which the currier can take down the leather in the same manner as a wright can take a shaving from a piece of wood with his plane. After the currier has thus levelled the hide or skin to his purpose, (which is always done on the flesh-side,) he spreads it out on a stone or table made for the purpose, and there scours it on the grain-side from all the loose tan, and other fluff that may hurt the beauty of the grain. He then puts on a certain quantity of oil on both grain and flesh side, for the purpose of softening the fibres, and at the same time making them tough, and hangs it up to dry. When it is sufficiently dry, there is a thin shaving again taken off the flesh-side, in order to clean or brighten it up; and then it is rubbed backward and forward upon a table by the currier with a nicked or furrowed board, keeping the leather always doubled at the place where he rubs, till it be made soft and pliable to his intention. This last part of the operation is properly called Currying, and it is from this that the business gets its name. As to the colour, the leather is fair or dark in proportion to the quantity of oil laid on, if the tanning has been properly performed, and the currier do not neglect some material part of his duty. Curriers seldom dye any colour but black, which is done with copperas and a very little logwood.

TANTALUS'S TANTALUS's cup. See Hydrostatics, p. 808.