IMITATION AND ARTIFICIAL SILK
Owing to the high price of pure silk and the bad wearing qualities of
the highly adulterated silks, described in the last chapter, there
has been for a long time a strong demand for a fabric which would
combine as far as possible the strength and wearing power of the one,
with the cheap price of the other, while still retaining the lustre
and “scroop” and characteristic appearance of both.
The demand at present is met, and not so unsuccessfully, first by
imitation silk, of which mercerized cotton is the best example, and
second, by the various forms of artificial silk which during the
last few years have been introduced widely in both Europe and our
own country. The competition of these two classes of products is not
at all to be despised. Their quality is constantly improving, their
price diminishing, and their production increasing rapidly from year
to year. And if the silk manufacturers continue to produce such poor
material in the line of weighted silk fabrics as they have in the
past, it will be but a short time before they will find the market
almost entirely divided between pure-dyed silks, on the one hand, for
expensive goods, and some of these new products for cheap materials.
MERCERIZED COTTON
_History and Preparation._—This material was first introduced as
a substitute for silk some ten or twelve years ago, although the
process for making it was invented about 1840, by a celebrated
English dyer, John Mercer. He discovered that when cotton, either in
cloth or yarn, was subjected for a short time to the action of strong
caustic alkali, and then thoroughly washed, the resulting material
was much stronger than before, had shrunk very considerably, and had
a much greater affinity for dyestuffs. For instance, dyes like the
Basic colors, which give but a temporary stain on ordinary cotton,
will dye with some degree of fastness cotton thus treated with
alkali, without the use of mordants. Mercer patented his discovery
and made some use of it in calico printing; as, for instance, in the
making of “crinkled” goods. But the process was nearly forgotten
until, in 1889, it was discovered that, by proper treatment, cotton
could by this means be made so lustrous as to compare not unfavorably
with silk.
To make the cotton lustrous, the goods, after dipping into the
strong alkali, are kept firmly stretched, and their strong tendency
to shrink resisted, until the alkali has been thoroughly rinsed off
and the last traces neutralized with a little acid. If this is done
carefully, when finally dried the cotton fibres will be found drawn
out smooth and lustrous, while still retaining their new qualities
of strength and increased dyeing power. To get good results in this
process the materials treated, whether in yarn or cloth, must
be made of the very best and longest stapled cotton, preferably
Egyptian, and when well done the results are extremely satisfactory.
The lustre is not as good as the very best silk, but it is quite well
marked, and for replacing the cheap grades of heavily weighted silks,
as, for instance, for underwear, linings, etc., the mercerized goods
are of very great value, owing to their strength and durability, as
well as their cheapness.
_Dyeing of Mercerized Cotton._—Cotton, thus treated, is dyed in
the same way that ordinary cotton is, with the exception that it
takes the dyes more rapidly, and, as a rule, gives deeper and more
brilliant shades with the same amount of coloring matter.
For special purposes it may be best to use the Sulphur or the Vat
dyes, but in general this material is best dyed with the Salt dyes,
which are not only easy to apply, but are fast to light, very
brilliant, and on these goods, at any rate, very fairly fast to
washing. As before mentioned, the fastness to both light and washing
may be considerably improved by after treatment of the dyed goods,
i.e., by passing them through a hot bath containing a tablespoonful
each of copper sulphate, potassium bichromate, and acetic acid to the
gallon of water.
This, however, will rarely be found necessary, provided the selected
colors are used, and the color has been applied at the boil in a bath
containing considerable salt.
ARTIFICIAL SILK
=History.=—The famous old French chemist, Réaumur, in the year 1734,
suggested, after a study of the silk worm, and of the method by which
it “spins” the natural thread, that it might be possible to make a
jelly-like substance which could be drawn out into a fine thread and,
coagulating, form an artificial silk.
This suggestion was first acted on, in a practical way, in the
year 1855, when Andermars obtained some curious results by dipping
a needle or fine metal rod into a thin viscous solution known as
collodion, and then drawing it out rapidly, made fine, smooth threads
as the material solidified. This collodion, which for many years has
been in common use in minor surgery to paint on wounds and cuts,
because it leaves a film of artificial skin, and in more recent times
has been much used in photography, is a solution of gun cotton or
nitro-cellulose in a mixture of alcohol and ether. In 1885 Count
Hilary de Chardonnet made improvements in this last process, and
produced successfully the first real artificial silk threads on a
commercial scale.
_Chardonnet Silk._—He also used a thick collodion solution, but
instead of _drawing_ it out he _pressed_ it out through fine holes
by using very great pressure. As fast as the gummy thread exuded it
was picked up, carried along into a drying room, where the alcohol
and ether could escape (to be condensed later and used over again),
and then the solid fibre was passed into a solution of some suitable
reducing agent, such as ammonium or sodium sulphydrate, which
converts the inflammable gun cotton into its original condition of
cellulose. These resulting threads, being smooth and uniform when
properly made, have very great lustre. Indeed, they are often far
more brilliant than the very best and finest natural silk, and can be
dyed and woven into beautiful fabrics.
This discovery of Chardonnet’s was at once utilized, and large and
flourishing factories of Chardonnet silk sprang up all over Europe.
The first large factory, which is still doing a very profitable
business, was at Besançon, in France, and later a large factory was
established at Frankfort, Germany.
_Pauly Silk._—The success of this process aroused the interest of
other chemists, and before long several rival processes came into
existence, also based on the use of a viscous solution of a cellulose
compound. One company, making the so-called Pauly silk, utilized the
solvent action of an ammoniacal copper solution upon cellulose for
their starting point.
_Elberfeld Silk, Glanzstoff._—The Farbenfabriken von Elberfeld,
famous manufacturers of dyestuffs, took up the manufacture of silk
from a solution of a compound of cellulose with acetic acid; and the
Elberfeld silk, or, as it is widely known in Germany, Glanzstoff,
is every year becoming a more and more important factor in the silk
business.
_Viscose Silk._—A still different process, which during the past
two or three years has been successfully introduced into the United
States, depends upon the curious substance called Viscose, a thick,
sticky solution of cellulose made by first treating wood pulp,
cotton or other vegetable fibre with strong caustic soda and then
dissolving the resulting product in carbon disulphide.
This Viscose was first introduced for many different purposes.
The solvent, carbon disulphide, is very volatile, and flies off
readily, leaving the cellulose behind in the form of a stiff jelly
which, on drying, becomes solid and strong. So Viscose was used for
water-proofing paper, etc., for making solid articles like piano
keys and billiard balls, and even for making opaque patterns in
calico printing. But its most valuable application is for artificial
silk. It is pressed out through fine holes, and the thread resulting
quickly solidifies as the solvent evaporates, and can be dried
carefully and worked up on reels or bobbins, to be dyed later.
_Properties._—Artificial silk, as a rule, is a little stiffer than
natural silk, but has an exceedingly fine lustre. It cannot be spun
in as fine threads as fine, natural silk, but, on the other hand, can
be produced in thick, smooth threads which, stained as a rule black
or dark colors, quite replace horsehair for furniture coverings, etc.
Similar products are made, too, by coating cotton with a layer of
artificial silk.
Another curious use of this artificial silk process is when it is
formed into still larger threads, very lustrous and quite stiff,
and used for plumes and aigrettes. They can be dyed any color, have
excellent lustre, and are extremely useful for millinery.
_Precautions Necessary in Dyeing._—One great drawback is common to
all these different varieties of artificial silk. They are quite
strong, although not particularly elastic, when dry, but when wet
lose their strength very markedly. Indeed, at one time it was
found extremely troublesome to dye them, as the silk skein dyers,
accustomed to work and wring and stretch their silk, with impunity,
in and out of the hot dye-baths, would try the same treatment
with this new product, and in consequence ruin every skein. When
thoroughly wet through in a hot bath the thread will soften until
a skein may hardly bear its own weight. Accordingly, the dyeing is
always done as quickly as possible, and generally at a lukewarm or
only moderately high temperature. The skeins should be handled as
little as possible in the dye-bath, and, when taken out to wring,
should be rinsed slightly to get rid of extra color, acid, etc., and
then carefully dried, not by twisting on two sticks, as is customary
with other materials, but by wrapping in cheese cloth or blotting
paper and then running the skeins backward and forward through the
clothes wringer.
=Tests for Artificial Silk.=—It has been ascertained that all
varieties of artificial silk now on the market are made from some
form of cellulose. Efforts have been made to take thick jellies
made from gelatine or similar animal compounds, and make threads
from them, coagulating them later by treatment with formaldehyde or
similar chemicals.
These experiments have, however, not as yet proved successful.
Accordingly, any test that will distinguish between a vegetable and
an animal fibre will show whether a brilliant thread or piece of
textiles contains natural silk or not. The simplest of tests is, of
course, to burn a little with a match or at a flame and see if there
results the characteristic “burnt feather smell” of charring animal
tissues. This odor accompanies the natural silk. The chemist would
probably make the same test more accurately by heating a wad of the
material in the bottom of a small test tube and noticing whether
ammonia was being evolved, and whether the distillate was alkaline
in reaction. The ammonia and alkali resulting from the nitrogenous
organic matter is a certain indication of animal matter.
To distinguish between mercerized cotton and artificial silk, it
is generally enough to soak the samples for a short time, say a
quarter of an hour, in boiling water and test their strength.
Mercerized cotton properly made would be just as strong afterward
as before, while the artificial silk would be soft and weak, if it
would not, indeed, break down completely. Besides this, it must be
remembered that the mercerized cotton, in spite of its lustre, is
made up of threads tightly spun together from a large number of short
fibres, none of which are over two inches or so in length, while
the artificial silks are made up, like the natural silk, of long,
continuous fibres twisted together to form the yarn.
In general, these artificial silks, manufactured as they are from
wood pulp and other vegetable materials, are to be dyed with the
Salt, Sulphur, or Vat dyes, care always being taken to expose them to
the action of hot dye-liquors as short a time as possible. The Salt
dyes are less apt to interfere with the brilliant lustre, but the
Sulphur and Vat dyes have the great advantage of dyeing in a cold or
lukewarm bath, without any loss in fastness.
The Chardonnet silk has a special affinity for the Basic dyes, and
in the trade is usually dyed both light and dark shades with these
coloring matters, without previous mordanting, in a slightly acid
bath. This practice, however, while simple and easy, is not to be
recommended. For the Basic dyes, with but few exceptions, fugitive
under all circumstances, are particularly sensitive to light, when
dyed in light shades, upon such a brilliant and almost transparent
medium as this is. On the other hand, articles made of artificial
silk, being easily injured by rain, are not so liable to be exposed
to the open weather as some other less delicate materials.
The Viscose and Elberfeld silks (Glanzstoff) have less affinity for
the Basic dyes, and dye more readily with the Salt and Sulphur colors
than the Chardonnet silk, made from gun cotton. But it is perfectly
possible to dye the latter also with fast colors of the Salt,
Sulphur, or Vat classes, providing large amounts of dyestuff are used
to bring up the shade. Indeed it is poor economy to be sparing of the
coloring matter, when working with any kind of artificial silk. For
speed is essential, and the dyer who lets his material remain long in
the dye-bath is liable to get into difficulties.
The artificial silk, after dyeing, should be finished much like
natural silk, by rinsing and then passing through a bath containing
some olive oil, emulsified in a weak bath of soda ash. This increases
the lustre. It should also be dried at a fairly low temperature and,
while drying, kept stretched out by hanging a wooden or glass rod in
the loop of the hanging skein, or some similar device, taking care to
avoid strain great enough to pull apart the weakened fibre.
When dyeing this material great care should also be taken in tying up
the individual skeins and in handling them. Turn them in the dye-bath
as little as possible consistent with even dyeing. The threads,
unless very tightly spun, are constantly liable to come untwisted,
and the knots to untie, causing much annoyance.
In conclusion, when carefully made and dyed these artificial silks
furnish beautiful, brilliant, lustrous fibres, which can be used to
great effect in many kinds of handicraft work. They can easily be
procured with more lustre than the very best natural silk, but even
when dry are deficient in elasticity, and to some extent in strength,
and when wet are very fragile. The price is kept at a rather high
figure, as a rule only from 25 to 50 cents a pound less than that
of good natural silk. But every year the production is increasing,
new factories are springing up in every country, and as there is no
limit to the production excepting the demand, it is probable that in
a few years, thanks to competition, the price will be dropped very
considerably and the whole silk business will be revolutionized. At
present it is estimated that the production of the artificial silk is
not far from one-fifth that of natural silk, and this fraction is
getting larger every month.
Indeed, the rise of this particular industry may fairly be considered
as one of the most interesting, most useful, and most valuable
contributions of the manufacturing chemist during the last quarter
century.