16 ChemMatters | FEBRUARY/MARCH 2018 www.acs.org/chemmatters
IN 2015, 1.24 BILLION PAIRS OF JEANS WERE SOLD AROUND THE WORLD, according to data compiled by Statistic Brain. On average, a pair of jeans requires 3 to 12 grams of indigo dye to turn them blue, and about 20 million kilograms of indigo are produced annually. That’s a lot of dye for a lot of jeans! But why and how is indigo used to give jeans their blue color, and where does all of this dye come from?
The original blue jeans
The California Gold Rush in the mid-1800s attracted entrepreneurs from all over the
world. One of those entrepreneurs was a Bavarian emigrant named Levi Strauss, who
headed to San Francisco in 1853 to establish a wholesale dry-goods business. He immediately noticed that gold miners and other laborers required durable clothing, particularly
Even though denim pants had been around as work wear for many years, the story of
jeans really begins with one of Strauss’s customers, a Nevada tailor named Jacob Davis.
In 1870, Davis was asked by one of his customers to make a pair of work pants for her
husband that wouldn’t fall apart. Davis tried to think of a way to strengthen his trousers
and came up with the idea of putting copper rivets at the points of strain, such as pocket
corners and the base of the button fly. These riveted pants were an instant hit. Davis
quickly decided to apply for a patent, but needed a business partner to help get the project
rolling. He immediately thought of Levi Strauss, his fabric supplier, and the first patent for
Levi’s jeans was issued in 1873.
The reason blue denim was more popular has quite a
bit to do with the indigo dye. Unlike most natural dyes
that, when heated, penetrate cloth fibers directly, indigo
binds externally to the cloth’s threads. With each
washing some of these dye molecules are stripped
away. The washing process individualizes the color
and also softens the rough fabric to individualize the
fit, as well. So, not only were Levi’s jeans durable,
they were comfortable.
Indigo dye can be produced naturally or synthetically. The most common natural
source for indigo is from the woad plant, which is native to tropical climates. But woad
flowers are yellow, and the leaves are green, so how is a blue-colored dye extracted from
BlueJeans INdiGO: By Jeffrey Deakin and Raymond Cooper