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Entry 1 - July 15th 2008

Indigo Dyeing Processes
Question emailed from customer.  "Why is there so much blue used in vegetable
dye oriental rugs?  What do they use?"-  Laura F. Lexington, KY

   Today we will discuss vegetable dye indigo.
   Blue is one of the most prominent colors that you will find in oriental rugs.  There
are two main reasons for this.  First, blue is a very pleasant color.  It conjures up all
kind of feelings and emotions, and is many times described as a “cool” color.  It
does not occur as often in nature as you might expect and can take on many
different shades in different types of light.  Secondly, blue is a simple, cheap, easy
dye color to make.  Even the Bedouins and Tribal Folk of Iran and Turkey have the
means necessary to create the dye and apply it.
   While the blue dye is common and easy to acquire, this does not in any way
lessen the amount of artistic skill required to use it masterfully.
   Natural Indigo is one of the more stunning forms of natural blue dye.  It can take
many variations of color and shades, and creates beautiful abrash (variations of
shades among the strand dye to inconsistency in the dye process.)
   India has the oldest indigo dyeing centers in the world, with production of the dye
pre-dating recorded history.  Present day Iran (old-world Persia) is credited with the
recipes used for applying the bright blue dye to wool.  The dye has been used for
purposes ranging from material dye, to ink, to paint, to cosmetics and medicines.
   The chemical structure that defines indigo is called Indigoten.  This chemical can
be created synthetically, and truly, most of the indigo used in production outside of
the oriental rug industry is synthetic.  But to a true master vegetable dyer, use of a
synthetic indigo is nothing short of sin.  Natural idigotin can be extracted from
multiple sources.  Most of the plants used for indigo extraction are from the
Indigofera genus, woad, dyers knotweed, anil, or natal indigo.
   The leaves from the chosen plants are cut, cleaned, and are then soaked in
water and fermented.  The fermentation processes a chemical called glycoside
indicant into the blue dye indigotin.  The original color of the solution is a murky
yellow.  As the fermentation takes place and the solution reacts with oxygen it
begins to take on a blue hue.
   One the process is fully complete, the leaf solution can be mixed with a strong
base chemical such as lye.  It is then pressed into cakes using cloth, dried in the
sun, and then powdered.  This powder can now be used as is or can be mixed with
other substances to create differing shades of blue, purple, browns, or black.
   The work is not quite finished yet.  You cannot simply mix the powdered indigo in
water and drop in your wool.  Indigo is not soluble in water, and wool has a natural
oil (lanolin) that will not allow the fiber to truly accept color.  The indigo powder must
be broken up a dissolved in a chemical process called reduction.  If you were to try
to use the dye at this point, it would combine with oxygen, revert to its insoluble
form, and make a big clumpy mess.  The easiest way to reduce the indigo is to mix
other material in the dye and heat it.  These materials can be bacteria cultures,
arsenic, or even stale urine.  Now the dye is water soluble and can be applied to
fabrics.
   Before the wool can be applied to the dye vat, it must be mordanted.  Remember
that wool is resistant to moisture and will not readily accept color.  It is structured
somewhat like a roofs shingles, with layers stacking upon each other.  Add the
lanolin oil to this equation and you will not easily allow the dye to “stick” to the wool
fiber.  The mordanting process forces the dye to “stick” to the wool fiber.  This is
done by creating an alkaline bath for the wool by mixing water and alum.  You can
pre-mordant the wool, or add the mordant to the dye, each method will create
different variations of color.
   Once the wool is mordanted and  placed in the dye, it is heated and stirred
regularly.  This process is still done in medium sized vats and is largely a cottage
industry.  It is easy to spot an indigo dyer, his hands are stained a deep inky clue.  
The wool is removed and as it dries and reacts with oxygen the blue color appears.
   When the correct shade of blue is achieved, the wool is washed with clean water
to end the react with oxygen by removing any excess dye.  Deeper colors may
require multiple dyeings, and all vats will be washed at least 4 times to ensure
quality and cleaniness.
   So the next time you look at vegetable dyed oriental rugs, spend some time and
admire the blues, particularly the more difficult lighter shades.  This is a dying art
form (no pun intended), and has recently seen a resurgence as buyers move
toward the old world look of vegetable dyes and hand-spun wools.
   If you would like to learn more about the art and creation of oriental rugs, check
out the rugs 101 section of our website, or email us with specific questions.
The RugMan's Blog
Natural indigo fermented and caked.
The beginning of a dye vat- notice the
murky yellow color.
Dye vats filled with cotton and wool.