Type 1.—In this a long mellow liming of 15-16 days is given, much like that described for harness leather in Section III., p. [72], Type 3. Only lime is used, but the liquors are not allowed to get dirty. The three-pit system is much the best. The hides are trimmed at the rounding tables, and then bated in hen or pigeon dung for three days at 75°-85° F. The deliming is commenced by washing in tepid water before bating, and is completed by a bath of boric acid, using up to 30 lbs. acid per 100 hides as necessary. In this and other processes for split hides it is essential to obtain all the lime out, but to do no plumping with acid. Lactic acid may also be used, but it is not so convenient to hit the neutral point with it.
The tannage consists of oak bark and myrabs together with gambier. These may be partly replaced by Natal bark, valonia, and quebracho respectively. It is sometimes desired to have a smooth finish, but sometimes to work up a "grain." In the latter case the hides are first put through colouring pits containing fresh leach liquor. In these they are constantly handled for a few hours. A little experience indicates which leach liquor will serve the purpose. The hides then go through the "green handlers" (8°-20°) in two weeks. The liquor is the old forward handler liquor made up with gambier. The hides may be sammed and split up at this stage, but the heavier goods may be tanned further. These heavies and the grains of the split hides now go through the "forward handlers" (20°-40°) for four weeks, and the heaviest goods given two layers (40°) of two weeks each, and making ten in all.
Type 2.—In this a shorter liming of 8-9 days is given with the help of sulphide. No dung bate is used, but the goods are washed with water and bated with ammonium chloride and boric acid. The tannage is chiefly of myrabs, but some valonia or Natal bark may be used together with chestnut extract and some quebracho. Gambier is used in the early liquors. The goods are coloured off in drum or paddle and tanned in several sets of handlers, viz. green handlers (15°-35°) three or four days; second handlers (35°-60°) two weeks; forward handlers (60°-80°) 1½ weeks; and floaters (80°-90°) for three weeks. The tannage is thus 6½ weeks in all. The arrangement of pits is a matter of local convenience, and the number of sets of equal strength is determined by the number of hides being tanned. The hides are split green or after passing through the green set. After tanning they are oiled with cod oil and dried out.
Type 3 is illustrated by American methods. The goods are tacked on laths or racks with copper nails in order to ensure smooth grain. They are then suspended in tan liquors. The tannage is largely with gambier and in weak liquors, which also help to give smooth grain. The tendency is to employ handler rounds involving a rather large number of pits, and to work these on the press system. Handling is also saved by plumping the liquors instead of shifting the goods forward, and by rocking the suspenders instead of handling up and down. The hides are split after about a month, and the heavier grains laid away in hemlock liquors.
Type 4.—This is a rapid process throughout. The hides are limed in 6-7 days with the help of sulphide, and "bated" by washing in warm water and then in cold to which hydrochloric acid is gradually added, finishing off again in tepid water. The hides are now coloured off in paddles, put through a small handler round (11°-20°) for half a week, and then split. The grains are drum tanned in a mixture of chestnut and quebracho extract, over a period of about three days in which the liquor is strengthened gradually from 30° to 50°. The fleshes are drum tanned with the old grain liquors after strengthening with quebracho.
The split hide grains for bag work, after tanning, are drummed in sumach, rinsed, drained, and oiled up to dry out, with some setting out. After wetting back they are shaved if necessary, hand scoured, and heavily sumached again to get a light even colour. The goods are slicked out, oiled up to samm, reset and dried out. They are next stained, sammed, printed by machine, dubbined or tallowed, "grained" (see Part II., Section I., p. [97]), brushed and rubbed with flannel.
REFERENCE.
Bennett, "Manufacture of Leather," pp. 202, 308.
SECTION X.—PICKING BAND BUTTS
It is the paradox of vegetable tannage that the less the pelt is tanned the stronger is the leather produced. The manufacture of butts for picking bands affords a good illustration. What is required is a leather of maximum toughness, pliability and durability. Any factor reducing the tensile strength of the leather is fatal. Hence, compared with most other tannages, picking band butts are under-tanned. To ensure the desired softness and pliability, moreover, it is necessary to have a mellow liming, rather heavy bating, and a soft mellow tannage in sweet and weak liquors. The required durability and the necessity for weak liquors both point to oak bark as the most suitable tanning material, assisted by some gambier in the early stages.