The scudding machine figured (Fig. 6) was invented by Sir John Turney in 1880,[17] and is the only type of machine which will safely scud split skins. It will readily be understood that the usual type of scudding machine, in which a spiral knife is used, would tear the delicate structure of the grain. The Turney scudding machine works with hard, circular brushes, which revolve against a wooden roller carrying the skin. At the same time a continuous stream of water, at a temperature of 110° F., is sprayed upon the skins from a perforated pipe.
After scudding, the skins are washed in cold water for about ten minutes. This checks the action of the puer, and also washes away any loose dirt. They are then ready to pass on to the drench (Chapter [IX].), or to the pickling process, or direct to the tan liquor, according to the kind of leather required.
The Bating of Hides for Harness or Dressing Purposes.—The hides intended for harness leather, or for dressing purposes, are usually bated with hen or pigeon manure. The exact process varies in different tanyards, being dependent upon the condition of the pelt prior to bating, as to whether it is bated directly after fleshing or receives a preliminary deliming. The process is also dependent upon the amount of bating action required for the specific purpose prior to tanning, but the following three methods are in actual use, and may be taken as typical methods:—
Harness Backs.—About a hundredweight of hen manure is put into a suitable tub or vat capable of holding about fifty gallons; some thirty gallons of water, at a temperature of about 100° F., is poured on to the manure, and the whole is thoroughly stirred up by means of a wooden stick or plunger, working the manure about in order to mix it to a consistence of thin soup. The vat is now stored in a warm place, so that the temperature is kept about 70° F.—it is customary to store this in the boiler-house, or some similar warm room. It should be stirred two or three times a day, until it begins to show signs of working; two days is generally sufficient for this.
A pit is now prepared, with the necessary amount of water; and, by the aid of a steam pipe, or other similar means, the temperature of the water is raised to 70°, and the contents of the bate tub are now added. This should be poured into the pit through a sack, or a canvas filter, so as to keep back stones, solids, feathers, and other extraneous matters. The pit is now thoroughly plunged, and the goods entered; these should be handled up three to four times a day for two days. At the end of two days the goods are usually scudded, by working the back on an ordinary unhairing beam with an unhairing knife. They then go into a fresh pit containing a new solution of bate made up in the same manner, and, when sufficiently bated, which generally takes about three days, the goods are removed from the pit, scudded again by working them over with a slate scudding tool, when they are ready for tanning. Some tanners give them a bath of boracic acid prior to their going into the tanning liquor; this has the effect of materially brightening the colour. The second pack of harness backs go into the same liquor—which must be re-warmed to a temperature of 70°—in which they are handled as before for about two days, and are finished off in a new liquor made as above described.
It will be understood, therefore, that in a tanyard, working regularly, the pack of backs go first into an old bate for two days, and are then finished off in a freshly made one; so that each pack gets two days in an old pit, and one or more days in the new. The bate in the tub may also have a second water, or be strengthened.
Dressing Hides.—For these goods a somewhat stronger bating effect is required, and pigeon manure is therefore frequently used. The preparation of the bating liquor is as described above, both as regards quantity and temperature of the water and time of maceration.
The whole process may be carried out exactly as described for harness backs, but the following is an illustration of another method in practical use. Imagine four ordinary bating pits, worked in a round. The first pit is very old, having had three packs of hides through it; the second having had two packs, and the third one pack; and the fourth is made new. The goods, after unhairing and fleshing, and washing, are put into the first pit quite cold, are handled in this three times on the first day, and afterwards put into the second pit, the temperature of the second pit having been previously raised to 65°—the cold pelt going into this pit reduces the temperature to about 60°. They are handled in this pit twice, and remain overnight; and the third day they go into the third pit, the temperature of which is raised to 70° before the goods go in. They are raised, scudded thoroughly on the grain, and new liquor is made from new bating liquor prepared as described above; the goods are now entered, handled at least twice a day, and, if insufficiently bated, are left overnight. By the next day they will probably be sufficiently “down” to permit of them going on to the scudding beam and thence on to tanning.
In the event of any hide being insufficiently bated—in other words, if the “bone” has not completely disappeared in the inner part of the hide—they are returned once more for three or four hours, the temperature of the pit being raised to 70° with a steam coil.
By this system, which is known as a system of “sets,” it will be noticed that the pits are worked in a round of four; the first pit, or oldest, being used more or less as a wash pit, the actual bating taking place in the second, third and fourth pits. No pit has more than four packs passing through it, and the temperature never rises above 70°, or, at the outside, 75°. The reason of the comparatively low temperature is due to the fact that in pit bating, if the temperature is raised above 75°, the grain of the hide becomes affected before the internal “bone” is sufficiently soft, which results in a tender grain, which considerably affects the resulting staining or dyeing which the leather usually receives before it is put on the market.