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People have always wanted to look great in clothing, but this was difficult to accomplish in ancient times. Almost all dyes then were plant based, which meant that colored fabrics would eventually fade. There were, in fact, only three dyes known in antiquity to be extremely permanent and intense. These were Tyrian purple (Argaman in the language of the Bible), royal blue (Tekhelet), and scarlet (Tola'at Shani). While scarlet was derived from an insect, both purple and blue were extracted from a snail, and the bromine atom plays a fascinating role in the creation of these colors.
Back then, Tyrian purple adorned the clothing of priests and kings, and was adored by the multitudes for its intensity and permanence. If you had even a stripe of purple on your garment, you would certainly be noticed in an otherwise drab sea of brownish, greenish, yellowish wraps. In ancient Rome, emperors were said to "take the purple upon themselves" as they dressed in royal togas dyed completely purple, and the historian Pliny cites "the mad lust for purple" at that time. But by the middle of the 4th century, if you weren't the caesar or one of his cadre, you could be put to death for wearing any purple at all. Thankfully, things changed and the fashion industry was born, all because a little snail in the Mediterranean had the ability to take bromine from the sea and bind it to indigo, forming dibromoindigo--Tyrian purple.
BROMINE AT A GLANCE
Name: From the Greek bromos, stench.
Atomic mass: 79.90.
History: Although it was first produced by a young German chemistry student, bromine's discovery is credited to French chemist Antoine-Jérôme Balard, who published a paper on it in 1826.
Occurrence: Occurs in seawater, underground salt mines, and deep brine wells, as well as some minerals.
Appearance: The only nonmetal that is a liquid at room temperature. Reddish-brown in color.
Behavior: Very volatile and extremely toxic. Bromine can cause severe burns on skin and its noxious vapors can irritate the nose and throat.
Uses: Mostly used as silver bromide in photographic film. Bromine was once used primarily in producing a leaded gasoline additive, ethylene dibromide, that prevents lead compounds from accumulating in engines, but the increased use of unleaded gas lowered demand for the additive. Also used in fire retardants, tear gas, fumigants, disinfectants, and pesticides.
BIBLICAL Though extract from the Murex trunculus snail is yellow, the dibromoindigo dye is responsible for both the brilliant purple and blue of antiquity.
COURTESY OF ARI GREENSPAN
The permanence of this snail dye is astounding. I traveled to the organic repository of the Israeli Antiquities Authority to see a purple ball of wool from Qumran, dating back to Roman times. As dusty boxes of bone and parchment were pushed aside, a magnificent tuft of Murex-dyed wool was revealed--as vibrant today as the day it was dyed.
The Bible commands that a blue string be worn on the corners of the Israelites' prayer shawls, a blue dyed with mollusk extract. The process of making blue dye for this ancient Jewish rite was lost as a result of Roman edicts and restrictions over 1,300 years. But my buddies and I were determined to rediscover its secret. On a blustery fall day, we donned our wet suits and air tanks to search for the small, slow Murex trunculus snail that houses the exquisite chemistry of nature's art.
As we rose from the deep with a cache of 150 snails, in a cove near the Crusader fortress of Akko, I felt like a link in the chain of history in the quest for the biblical blue dye. The Arab children crowding around our hoard of snails were shouting their word for mollusk, "chilzun, chilzun." I trembled as I realized that their "chilzun" echoed the Talmud's Aramaic name for the creature--"chilazon." With great excitement we began to extract dye from the snail.
Our first glimpse of this proud bromine-based dye from hoary antiquity revealed a humble, clearish yellowish substance. Exposure to the air triggered a complex enzymatic reaction that transformed the liquid through the entire color spectrum until, within minutes, before our very eyes, the single drop of dye was an intense deep purple.
But if the snail we collected was identical to the one described by the rabbis over two millennia ago, why did it not produce the proscribed blue for our fringes? Why were we seeing only purple? The amazing answer to this conundrum, which baffled 20th-century scientists for decades, was discovered in the chemistry lab. In order to use this odoriferous dye, the snail extract must be reduced to achieve a solution. When this process is performed indoors, the result is a purple dye. But if, while in its reduced state, the dibromoindigo is exposed to the sun for a few minutes, the bromine invisibly breaks away from the molecule, leaving behind only indigo, the brilliant biblical blue.
The Talmud equated the color of the Tekhelet dye to the color of the depths of the ocean and heights of the sky. We now understand how the chemistry of a lowly sea snail and the exalted bromine atom yield a world rich in color, complexity, and permanent beauty.
Ari Greenspan is a dentist practicing in Jerusalem and the director of the P'til Tekhelet (http://www.tekhelet.com). His interests range from biblical archaeology to medieval painted glass and from blacksmithing to gold-leaf illumination.
Chemical & Engineering News
Copyright © 2003 American Chemical Society
