3. The third type consists of a short three-month's tannage in which the liquors are worked straight down the yard. To compensate for the short time it is necessary to have stronger layer liquors in which the goods spend a still greater proportion of their total time. The stronger liquors involve a greater proportion of extract, particularly of quebracho, which fact causes the whole of the liquors to be sharper than their Bkr. strength indicates, and justifies them being worked straight down the yard.
The goods go through suspenders (20°-40°) as usual one week, and then pass into suspender-handlers (40°-60°) for two weeks, and thence to the layers. In the first two of these (65° and 70°) they are actually in suspension, a week in each liquor. They are then dusted down for ten to eleven days, first in 85° and then in a 95° liquor, and finally for a month in a liquor of 110°. The total tannage is thus twelve weeks, of which nine weeks (75 per cent.) are in layers. There is considerably less handling than in Type 2, and it is more convenient, the goods being in suspension.
4. The fourth type is also a three-month's tannage. In this it is attempted to obtain even greater weight with still less labour. The layer liquors are kept much stronger by the more extensive use of extract, and this makes it impracticable as well as too costly to run these liquors down the yard. They are therefore repeatedly strengthened with extract and used again.
The goods go through suspenders (20°-40°) as usual one week, and then through a round of suspender-handlers (40°-55°) consisting of fresh sharp liquor from the leaches together with quebracho extract. They are in this set two weeks, and then are laid away. They receive three layers: first, 105° for 2 weeks; second, 110° for three weeks; and finally, 120° for a month. Of the twelve weeks, therefore, nine weeks (75 per cent.) are spent in layers. In this method the goods are immersed in 3 per cent. sulphuric acid after passing through the suspenders.
There is possible, of course, a tremendous number of variants of the above types. The number of handler rounds is determined by the number of butts being dealt with. With a large number it is more easily possible to arrange for them to be in progressive strength as in Type 1. There are also many systems of working the layers, of which the most notable is to make the second or third layer from fresh leach liquor and extract, and strengthen it with extract for the succeeding layers. It is then used as a first layer and worked down the yard.
The bellies and shoulders often go through separate sets of liquors, but it is common to put them through suspenders, and even handlers together. They receive, of course, a distinctly shorter tannage, and are often drummed with extract before laying away or after the first layer. By way of illustration, the course of the offal and their liquors may be given in the case of Type 1. The shoulders and bellies are coloured off in a paddle or drum with old butt suspender liquor, which is then quite exhausted. They then pass through suspenders (18°-40°) together in 4-5 days, and go through a handler round (40°-55°) for 3 weeks, including one duster. The bellies are removed after 2 weeks, and given three layers (60°, 70°, 80°) of a week each. They receive, therefore, nearly 6 weeks in all. The shoulders also have three layers (60°, 65° and 80°) of 2, 3 and 4 weeks respectively.
The course of the liquors is shown thus:—
The tanned butts are piled for 2-3 days, sometimes rinsed to remove dusting material, and then scoured either by machine or by drumming with sumac and extract. This removes bloom, but causes some loss of weight. "Vatting" or "bleaching" now follows, in which it is attempted not only to bleach the colour of the leather, but also to impart as much weight as possible. The vat liquor is made several degrees stronger than the last layer by means of quebracho bleaching extract and good coloured chestnut or myrabs extract. The liquor is kept warm by a steam coil, at about 100° F., but not much more without risk. The goods remain in the bleach liquor 2-3 days and are then horsed or suspended to drain. Sumach is sometimes used in the vats. A new vat liquor must be made up after some weeks' use. The goods are sometimes rinsed in weak sumac liquor before vatting to get good penetration, and sometimes after to ensure good colour.
The butts are next oiled and hung up in a dark shed and allowed to dry slowly and evenly to an "india-rubbery" consistency and rather slimy feel. They are then "struck out" by machine, wiped, re-oiled and again hung up to dry, preferably with sulphonated oil. After a short drying to a suitable and even condition they are "rolled on," and, possibly after further drying, "rolled off" with greater pressure, and then dried for a day or two with the help of a little steam. Finally they are machine brushed and sent to the warehouse, where they are weighed and classified.