Indigo dye
is an important
dyestuff
with a distinctive blue
color (see
indigo).
The natural dye comes from
several species of
plant, but nearly all
indigo produced today is
synthetic. Among
other uses, it is used in
the production of
denim
cloth
for blue
jeans.
Learn more about denim jeans
from the
Denim Dictionary.
Sources and uses
A variety of plants have
provided indigo throughout
history, but most natural
indigo is obtained from
those in the genus
Indigofera, which
are native to the tropics.
In temperate climates
indigo can also be obtained
from
woad (Isatis tinctoria)
and
dyer's knotweed (Polygonum
tinctorum), although
the Indigofera
species yield more dye.
The primary commercial indigo
species in
Asia was true indigo
(Indigofera tinctoria,
also known as Indigofera
sumatrana). In
Central and
South America the two
species Indigofera suffructicosa
and Indigofera arrecta
(Natal indigo) were the
most important.
Natural indigo was the
only source of the dye until
about 1900. Within a short
time, however, synthetic
indigo had almost completely
superseded natural indigo
and today nearly all indigo
produced is synthetic.
In the
United
States, the primary
use for indigo is as a dye
for cotton work clothes
and blue jeans. Over one
billion pairs of jeans around
the world are dyed blue
with indigo. For many years
indigo was used to produce
deep navy blue colors on
wool.
Indigo does not bond
strongly to the fiber, and
wear and repeated washing
may slowly remove the dye.
History
Indigo is among the oldest
dyes to be used for textile
dyeing and printing. Many
Asian countries, such as
India, China, and Japan,
have used indigo as a dye
for centuries. The dye was
also known to ancient civilizations
in Mesopotamia, Egypt, Greece,
Rome, Britain, Peru, and
Africa.
India is believed to
be the oldest center of
indigo dyeing in the Old
World. It was a primary
supplier of indigo to Europe
as early as the Greco-Roman
era. The association of
India with indigo is reflected
in the Greek word for the
dye, which was indikon.
The Romans used the term
indicum, which
passed into Italian dialect
and eventually into English
as the word indigo.
In Mesopotamia, a Neo-Babylonian
cuneiform tablet of
the 7th century gives a
recipe for the dyeing of
wool, where lapis-colored
wool (uqnatu) is produced
by repeated immersion and
airing of the cloth. Most
probably, indigo was imported
from India.
The Romans used indigo
as a pigment for painting
and for medicinal and cosmetic
purposes. It was a luxury,
however, being imported
from India to the Mediterranean
by Arab merchants. Indigo
remained a rare commodity
in Europe throughout the
Middle Ages, so
woad was used instead.
In the late
fifteenth
century,
the Portuguese
explorer
Vasco da
Gama discovered
a sea route
to India.
This led
to the establishment
of direct
trade with
India, the
Spice Islands,
China, and
Japan. Importers
could now
avoid the
heavy duties
imposed
by Persian,
Levantine,
and Greek
middlemen
and the
lengthy
and dangerous
land routes
which had
previously
been used.
Consequently,
the importation
and use
of indigo
in Europe
rose significantly.
Much European
indigo from
Asia arrived
through
ports in
Portugal,
the Netherlands,
and England.
Spain imported
the dye
from its
colonies
in South
America.
Many indigo
plantations
were established
by European
powers in
tropical
climates;
it was a
major crop
in Jamaica
and South
Carolina.
However,
France and
Germany
outlawed
imported
indigo in
the 1500s
to protect
the local
woad dye
industry.
Indigo was
the foundation
of centuries-old
textile
traditions
throughout
West Africa.
The use
of indigo
here pre-dated
synthetics.
From the
Tuareg nomads
of the Sahara
to Cameroon,
clothes
dyed with
indigo signified
wealth.
Women dyed
the cloth
in most
areas, with
the Yoruba
of Nigeria
and the
Manding
of Mali
particularly
well known
for their
expertise.
Among the
Hausa
male dyers
working
at communal
dye pits
were the
basis of
the wealth
of the ancient
city of
Kano, and
can still
be seen
plying their
trade today
at the same
pits.
In 1865
the German
chemist
Johann
Friedrich
Wilhelm
Adolf
von
Baeyer
began
working
with
indigo.
His work
culminated
in the
first
synthesis
of
indigo
in 1880
and the
announcement
of its
chemical
structure
three
years
later.
BASF
developed
a commercially
feasible
manufacturing
process
that was
in use by
1897, and
by 1913
natural
indigo had
been almost
entirely
replaced
by synthetic
indigo.
In 2002,
17,000 tons
of synthetic
indigo were
produced
worldwide.
Developments
in dyeing
technology
Indigo
is a challenging
dye to use
because
it is not
soluble
in water;
to be dissolved,
it must
undergo
a chemical
change.
When a submerged
fabric is
removed
from the
dyebath,
the indigo
quickly
combines
with oxygen
in the air
and reverts
to its insoluble
form. When
it first
became widely
available
in Europe
in the sixteenth
century,
European
dyers and
printers
struggled
with indigo
because
of this
distinctive
property.
A preindustrial
process
for dyeing
with indigo,
used in
Europe,
was to dissolve
the indigo
in stale
urine. Urine
reduces
the water-insoluble
indigo to
a soluble
substance
known as
indigo
white
or leucoindigo,
which produces
a yellow-green
solution.
fabric dyed
in the solution
turns blue
after the
indigo white
oxidizes
and returns
to indigo.
Synthetic
urea
to replace
urine became
available
in the 1800s.
Another
preindustrial
method,
used in
Japan, was
to dissolve
the indigo
in a heated
vat in which
a culture
of
thermophilic,
anaerobic
bacteria
was
maintained.
Some
species
of such
bacteria
generate
hydrogen
as a
metabolic
product,
which
can
convert
insoluble
indigo
into
soluble
indigo
white.
Cloth
dyed in
such a
vat was
decorated
with the
techniques
of
shibori
(tie-dye),
kasuri,
katazome,
and
tsutsugaki.
Examples
of
clothing
and
banners
dyed
with
these
techniques
can be
seen in
the
works of
Hokusai
and
other
artists.
