MANUFACTURE OF THROWN AND SPUN SILK
We have covered in the preceding chapters the culture of raw silk,
its reeling, and finally its marketing in the countries where it is
to be manufactured into the finished textile. We now come to the
mechanical phases of the industry, by which raw silk is made first
into yarn and then into fabric. Whereas, in the case of cotton and
wool, we have seen that yarn is manufactured by various modifications
of the spinning process, this is not true in the case of silk.
The spinning process is here supplanted by an operation known as
“throwing,” and is resorted to only in the manufacture of yarn from
the various kinds of silk waste.
1. THROWN SILK
[Sidenote: _Necessity for Throwing_]
The ordinary raw silk, as it comes from the filature and is sold
in the market, is composed of from two to eight filaments adhering
together by virtue of the natural gum secreted by the worm.
This thread is too thin and delicate for many uses and so must
be submitted to further twisting and doubling—a process called
“throwing.” It must be borne in mind, however, that there are several
types of fabrics in which raw silk is used without going through the
throwing operation. This is usually the case, for example, with the
warp threads for crepes, charmeuse, and messaline.
[Sidenote: “_Throwsters_”]
Although some of the larger silk mills have their own departments for
this process, as a general rule it is done by independent concerns
known as “throwsters”—who specialize in this particular operation.
Machinery of a very complicated and accurate type is necessary,
capable of operating at very high speed. It has been found that the
investment called for to equip such a mill is too large in most cases
to allow the manufacturers to incorporate this operation in their
factories, particularly if it happens that the spindles are not
fully employed during the whole of the year.
[Illustration: _Throwing Machines_]
[Sidenote: _Organzine and Tram_]
There are two main classes of thrown silk—organzine and tram—the
former has a heavy twist and is used for the warp; while the latter
is given only a light twist and is used for filling. Within these two
general types there are many special grades, according to the type
of material for which they are to be used, such as crepe, chiffon,
sewing thread, floss silk, embroidery silk, etc.
[Sidenote: _Soaking the Raw Silk_]
The raw silk as it comes to the throwing mill is done up in books
of skeins and packed in bales, as described in a previous chapter.
The skeins, after being weighed and examined, are first soaked for
about twelve hours in warm soapy water, which softens the natural
gum, after which they are thoroughly dried. This, of course, reduces
the moisture content below the customary 11 per cent, which is later
restored by natural absorption.
[Sidenote: _Winding_]
The first step in the actual throwing is the winding of the thread on
bobbins. The skeins are put on swifts—a light type of reel—and wound
at a very high rate of speed on the proper size of bobbin. It is here
that the winding strength of the silk meets its severest test, for
constant breaks during the winding involve considerable expense when
speed is such an important factor.
[Sidenote: _Twisting_]
The bobbins of silk are next taken to the twister, which combines
two or more strands and gives the thread the necessary amount of
twist for the special type that is desired. In the case of tram a
very light twist is given, about two or three turns to the inch. For
organzine the single threads are first given sixteen turns to an inch
in one direction, then doubled and twisted fourteen turns in the
other direction.
[Sidenote: _Crepe_]
Twisting is the basis of the manufacture of the various kinds of
crepe. The filling or tram used is given a very hard twist, about
sixty-five turns to the inch—either in right or left-hand direction.
These threads are later woven alternately and so produce the crinkled
effect.
Thrown silk is classified in a similar way to raw silk, except that
usually market quotations on thrown silks mention not only the
classification but also the purpose for which it is to be used (tram
or organzine), the size in deniers, the number of threads and twists
to the inch.
2. SPUN SILK
[Sidenote: _Spinning Waste Silk_]
The above processes refer only to throwing of raw silk. In the case
of waste, schappe, frisons, etc., an entirely different method must
be used, comprising a series of operations very similar to the
carding, combing and spinning of wool.[8] The gum, of which silk
waste contains a very large proportion, must first be boiled off in
a hot soapy bath or allowed to ferment in vats, the latter method
being used more generally in Europe. After degumming, the waste
silk is next washed and dried and allowed to absorb the 11 per cent
moisture content, as in the case of the thrown silk. This is followed
by picking, combing, and dressing to remove any dirt or other foreign
matter and to separate the fibres and arrange them in parallel order.
The silk is next separated into short laps, then drawn out into thin
slivers by means of drawing frames, and thoroughly combed to make the
fibres smooth and uniform. These slivers are finally made suitable
for winding on bobbins by being passed through roving frames. Then
follows the actual spinning process, which twists the roving into
yarn. Different types of yarn are produced by varying the amount of
twist and the number of strands used. Single yarn is made by twisting
a single strand on itself, while for 2-ply, two yarns are twisted
together, and so forth, as in the case of cotton or wool.
After being cleaned and examined, the yarn is wound into skeins of
about 5 ounces.
[Sidenote: _Uses of Spun Silk_]
The principal use of spun silk is in mixed fabrics, in conjunction
with wool, cotton, or raw silk, the spun silk thread generally being
used as filling rather than warp. The better grades are made into
velvet and plush and various types of knit goods. Although high
quality spun silk often has the strength and wearing quality of
thrown silk, it never can compete with the latter in regard to lustre.
[Sidenote: _Sizing_]
Spun silk is described as to size in one of two general ways. In the
English system the number of the yarn is the number of hanks of 840
yards weighing a pound, with a second number indicating the ply.
Thus, size “20-2” would designate a 2-ply yarn, a pound of which
contained 16,800 yards. The French system is more or less on the same
principle, the main difference being that the number of the yarn
indicates the thousands of metres weighing a kilogram.
[8] See Part Two, Page 74 to Page 78 for details of spinning.
3. MARKETING THROWN AND SPUN SILK
Thrown and spun silk are bought and sold in very much the same way
as is raw silk, although the market is not as extensive nor is the
volume of trading as large. The following tables of quotations are
from a recent silk journal. A comparison with the quotations given
in Chapter III will show the appreciation in value of the various
gradings through the throwing and spinning processes.
THROWN SILK
ORGANZINE
Double Extra Crack $7.30
Double Extra 7.20
Extra 7.10
TRAM
Extra $6.85
Best No. 1 6.75
Kansai No. 1 6.70
Japan Crepe Twist, 2 thread, 75 turns 7.80
Japan Crepe Twist, 3 and 4 thread, 60-65 turns 7.25
Canton Crepe Twist, 3 and 4 thread, 60-65 turns 7.20
Hosiery Tram 6.75
SPUN SILK
2% net 30 days
6/2 $4.25
10/2 4.35
20/2 4.75
30/2 5.15
40/2 5.35
50/2 5.50
60/1 4.45
60/2 5.60
[Illustration: _Twisting on New Warp Threads_]
[Illustration: _Modern British Loom_
Shown at the British Empire Exposition
Wembley, 1924]
[Sidenote: _Imports_]
Although far from approaching raw silk, the importations of silk
waste to this country reach quite substantial figures, as the
following table shows:
Raw Silk Waste Silk
1920 30,058,374 9,400,985
1921 45,355,095 6,849,369
1922 50,711,826 7,638,317
1923 49,505,581 12,101,420
(Courtesy of Silk Association of America)