The offal is often drum oiled. It needs more striking and is more
difficult to obtain in suitable condition for striking, rolling. It is
treated similarly to butts, but often also goes for dressing leather,
and may be split. It is of some interest to compare the above processes
with that once very popular manufacture of "bloomed butts" in the West
of England from South American salted hides. These receive a liming from
12-14 days, using 12-16 lbs. of lime per hide. They receive then a
tannage of about 9 months, comprising 3 weeks in suspenders
(20°-40°)--very sour and mellow liquors--4 weeks in handlers (40°-55°),
4 weeks in dusters (60°), 4 weeks in round made from hemlock extract
(60°), and 20 weeks in six layers (60°-90°) in which they were dusted
heavily with valonia. Oakwood extract was used for the layers, which
took 57 per cent. of the total time. The butts were scoured in a
much-dried condition, so that only the loose and surface bloom was
removed. No bleaching was given in the modern sense.
In the old oak-bark tannage of sole leather up to 12 months were taken
for tanning, two-thirds to four-fifths of which time the goods were in
layers. The strongest liquor rarely exceeded 50° even where valonia and
gambier were also used, and rather more than 30° if not.
It will be understood from the above that the tendency for many years
has been to shorten the time and the labour required for tanning. Drum
tanning is obviously the next stage in shortening the time. In one such
process the butts are put through suspenders (25°-40°) for 2 weeks,
drummed for 12 hours in an 80° extract liquor, and finally in a neat
extract 200° for 36 hours. Drum tanned sole leather, however, is not as
yet of good quality; the grain is not smooth, and the heavy weight
finish (striking and rolling) needed to counteract this tendency is
liable to cause poor "substance." The leather, too, readily wets and
goes out of shape. Possibly some drumming may be adopted to save time in
the early layers, but the most serious rival to the 3 months' tannage is
the waterproof chrome sole leather (Part III., Section V.).
REFERENCES.
Parker, _J.S.C.I._, 1902, 839.
Procter, "Principles of Leather Manufacture," p. 220.
Bennett, "Manufacture of Leather," pp. 179, 259.
Bennett, _J.S.C.I._, 1909, 1193.
SECTION VI.--BELTING LEATHER
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