Touched by Indigo - Royal Ontario Museum

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INDIGO
The Chinese obtain blue dye from
several plants. Among them the liaolan
(Polygonum tinctorium) is the most
popular. This is an annual herbaceous
plant having alternating bluish-green
leaves on a fleshy stem. Its small flowers
range in shade from white to dark
pink. Some believe that the pink-flower
varieties yield more dye than the white
ones.
Liaolan has been cultivated in
China since the Zhou dynasty. Over
time, this useful plant became more and more widely grown. In
China's eastern province of Zhejiang, the best indigo is produced
from the village of Huangtandong near the city of Yueqing. Their
traditional method of production is briefly described here.1
The plant is harvested in mid-October when it reaches about 85
cm tall. Women and children help to pick the leaves and tender twigs
that will be used to make indigo dye. The denuded stalks are then cut
at about 4 cm above the ground, tied into bundles, and stored away
to be replanted in the spring.
The production process, which takes approximately twenty
days, is undertaken by men only. It takes place on a gentle slope
in the field where three artificial ponds have been dug.
The largest, measuring 2 m in diameter and 1 m deep,
is situated in the middle. It is flanked by two smaller
ones located one above and the other below. During the
first week, the leaves and twigs are thoroughly soaked
in water in the big pond. They need to be stirred three
times a day to ensure even fermentation and release of
the dye matter.
The decomposed leaves and twigs are then scooped
up and placed in the upper pond. At this time slaked lime
(calcium hydroxide) is added to the liquid left in the big pond.2 This
step needs great care since the amount added is critical to the quality
of the end-product. First, two people
use a wooden bucket with two long
upright handles to scoop out some liquid.
While one person keeps stirring the
liquid in the bucket, the other adds the
slaked lime. When a suitable amount
has been added, they lower the bucket
into the pond until its rim is about the
same level as the liquid in the pond.
Turning the bucket in a circular motion
all the time, they gradually add the
mixed liquid to the indigo in the pond,
taking care not to let the residues in the
bucket spill over into the pond. This
step has to be repeated four times. How
much slaked lime should be mixed into
the indigo is judged by tasting. When
the indigo is bitter to the taste, it means it has attained its optimum
alkalinity.
The next step must be done either before sunrise or after sunset
so the dye-maker can judge the hue of the indigo unaffected by sunlight.
Standing on opposite sides of the pond,
each man uses a wooden plough to push and
stir the liquid towards the centre. Thirty minutes
of this vigorous stirring causes a thick
and fast-moving frothy foam to gather on
the surface. When the foamy layer reaches a
height of 30 cm, one of the men adds a few
spoonfuls of vegetable oil. At this point they
switch tools, now using skimpily constructed
long-handle scoops to continue to stir and