Four types of sole butt tannage will now be described, all of which illustrate the methods employed in a modern mixed tannage.
1. The first type consists in a four-months tannage, in which the liquors are worked down the yard.
The butts pass first through the suspenders (20°-40° Bkr.) in about a week, and are rocked in the first liquors. They next enter the handlers (40°-55°) rounds of eight pits, six floaters and two dusters. Myrabs, or a mixture with algarobilla is used as dusting material. The goods remain in this set for two weeks, and should then be struck through. The suspender handlers (55°-65°) are next entered, in which they remain up to three weeks in suspension, being shifted forward on alternate days. The goods now enter the layers, of which four are given: first 70° for one week; second 75° for two weeks; third 80° for three weeks; and fourth 90° for a month. The goods thus take sixteen weeks to tan, of which ten weeks (62½ per cent.) are in layers.
The system of working the liquors is expensive, and is only possible if the butt liquors can be spent out by the offal. The best or fourth layer, 90°, is made from the best leach liquor, 65°, and extract (chestnut with some oakwood or mimosa bark). After use it becomes the second layer, 75°. The third layer, 80°, is also made from fresh leach liquor and extract (chestnut with some myrabs or mixed extract). After being used thus it is used for the first layer, 70°. The used first and second layers are mixed together and used partly to form the belly layers, and partly to make a sharp liquor for the handlers (55°-40°) by diluting with 40° leach liquor and adding quebracho extract. The old handler liquor is run to the suspenders (40°-20°), and finally used for colouring off the offal in drum or paddle 18°. The suspender handlers (65°-55°) are made from fresh leach liquor and chestnut extract. They are afterwards used to make shoulder layers. The course of the liquors is shown on p. [59].
It will be seen that fresh leach liquor and fresh material are used to each set except the suspenders, which must have some mellowness to ensure plumping and smooth grain. Layer liquors are used twice only, and then (when only five weeks old) pass to the handlers. These are further sharpened by fresh leach liquor and fresh extract and dry materials. The forward handlers are fresh liquors with fresh extract. This tannage is fairly typical of high-class sole leather, in which the liquors are worked down the yard, but worked towards the offal, which thus receives liquors with relatively greater proportions of mellow tans and soluble non-tans.
2. The second type consists in a tannage of about four months, in which the liquors are not worked down the butt yard. In this method also there is an attempt to save much of the labour in handling, first by shortening the time in the handlers by one week (as compared with the above), and second by fusing the two progressive handler sets into two sets of equal strength, through which the goods pass more slowly and with less disturbance.
The goods go through the suspenders (10°-25°) in about a week, rocking in the early liquors, and then into large rounds of handlers (30°-45°) for one month. The handlers consist of floaters and several dusters, in which the butts are laid away with 1-3 cwt. myrabs. The goods next enter the layers, of the same strength as in Type 1, and in which they remain the same time. The total tannage is thus 15 weeks, of which 10 weeks (nearly 67 per cent.) are in layers.
The best or fourth layer is made up from leach liquor and extract, and is then used successively as a third, second and first layer, and then passes to the offal layers. The handler liquor is made entirely from fresh leach liquor and quebracho extract, and is a sharp liquor of greater strength than its Bkr. strength would indicate. The old handler liquor is run to the butt suspenders. The course is represented thus:—
