271
15
the water-insoluble indigo is reduced with
a reducing agent such as sodium dithionite
(Na 2 S 2 O 4 ) in an alkaline solution to the colorless
water-soluble indigo white, the so-called leuco
form (. Fig. 15.7). This dye liquor is called “vat”.
This term is originally derived from the tub in
which these dyeing processes were carried out.
The fibers, preferably cotton or viscose fibers
(7 Chap. 7), are dipped into this vat. As already
described above, the indigo white on the fiber is
converted into the dye indigo in the presence of
atmospheric oxygen. Several dyeing processes are
necessary to achieve a strong blue color.
Indigo had its great success in the middle
of the nineteenth century when Levi Strauss
dyed his denim trousers for gold diggers with
indigo in San Francisco. Over time, these trousers developed into blue jeans (. Fig. 15.8), of
which more than a billion are currently sold
every year. To produce them, approximately
30,000 tons of indigo are needed, which are no
longer of natural origin, but are produced synthetically (cf. BOX: Indigo - Yesterday, Today and
Tomorrow).
was fermented at temperatures of approx. 35 °C
to a brownish broth. Urine was added during this
fermentation. Indican, a β-d-glucoside of indoxyl,
present in the leaves, was dissolved and cleaved by
the enzyme β-glucosidase (. Fig. 15.7). The broth
was then poured off from the plant residues. It
was continued in two different ways:
5 In order to obtain the pure dye, the
indoxyl-containing liquid was beaten in the
air with rods and slats for several hours. Oxygen got into the solution and the water-soluble, colorless indoxyl oxidized and dimerized
to the water-insoluble deep blue indigo. This
precipitated in the form of flakes and could
be collected, dried and pressed into pieces.
5 If textiles were to be dyed directly
(. Fig. 15.8), the fabrics were immersed in
the indoxyl-containing solution, removed
and then dried in the air. Here, too, the
indoxyl spontaneously reacts to form small
indigo particles which adhere to the fiber.
The principle of vat dyeing is used to dye a textile with the isolated indigo. For this purpose,
. Fig. 15.8 Indigo, the color of blue jeans (© Juanmak, Wikipedia)
15.4 · Indigo, the “King of Dyes”
15
the water-insoluble indigo is reduced with
a reducing agent such as sodium dithionite
(Na 2 S 2 O 4 ) in an alkaline solution to the colorless
water-soluble indigo white, the so-called leuco
form (. Fig. 15.7). This dye liquor is called “vat”.
This term is originally derived from the tub in
which these dyeing processes were carried out.
The fibers, preferably cotton or viscose fibers
(7 Chap. 7), are dipped into this vat. As already
described above, the indigo white on the fiber is
converted into the dye indigo in the presence of
atmospheric oxygen. Several dyeing processes are
necessary to achieve a strong blue color.
Indigo had its great success in the middle
of the nineteenth century when Levi Strauss
dyed his denim trousers for gold diggers with
indigo in San Francisco. Over time, these trousers developed into blue jeans (. Fig. 15.8), of
which more than a billion are currently sold
every year. To produce them, approximately
30,000 tons of indigo are needed, which are no
longer of natural origin, but are produced synthetically (cf. BOX: Indigo - Yesterday, Today and
Tomorrow).
was fermented at temperatures of approx. 35 °C
to a brownish broth. Urine was added during this
fermentation. Indican, a β-d-glucoside of indoxyl,
present in the leaves, was dissolved and cleaved by
the enzyme β-glucosidase (. Fig. 15.7). The broth
was then poured off from the plant residues. It
was continued in two different ways:
5 In order to obtain the pure dye, the
indoxyl-containing liquid was beaten in the
air with rods and slats for several hours. Oxygen got into the solution and the water-soluble, colorless indoxyl oxidized and dimerized
to the water-insoluble deep blue indigo. This
precipitated in the form of flakes and could
be collected, dried and pressed into pieces.
5 If textiles were to be dyed directly
(. Fig. 15.8), the fabrics were immersed in
the indoxyl-containing solution, removed
and then dried in the air. Here, too, the
indoxyl spontaneously reacts to form small
indigo particles which adhere to the fiber.
The principle of vat dyeing is used to dye a textile with the isolated indigo. For this purpose,
. Fig. 15.8 Indigo, the color of blue jeans (© Juanmak, Wikipedia)
15.4 · Indigo, the “King of Dyes”