Copyright 2002 by Lois Fruen
This article accompanies the textbook The Real World of Chemistry 6th ed by Lois Fruen Kendall/Hunt Publishing ISBN 0-7872-9677-5
Techniques for dying ancient textiles were described by classical authors such as Pliny the Elder and Aristotle (Koren 270). Today the Edelstein Center for the Analysis of Middle Eastern Textiles and Related Artifacts at Shenkar College of Textile Technology in Ramat-Gan Tel Aviv specializes in studying those processes and analyzing ancient textile dyes.
People have been dying cloth for at least 6000 years. Archaeologists have found a number of ancient pieces of dyed fabric and other evidence for ancient textile dying. One of the most important finds was a 6000 year-old 23-foot long red-dyed linen cloth that was recently discovered in the "Cave of the Warrior," a major Neolithic site in Israel. Ancient dyed garments were also found at Masada (Orna 373). Sheeps wool that was dyed red with madder and blue with indigo was found at Kahun, an Egyptian town for pyramid workers, dating to 1890 BC (Bahn 318). Egyptian tomb paintings at Beni Hasan also show nomadic people wearing multi-colored garments and shoes, and a model dating to 2000 BC from the tomb of Meketra at Thebes shows a weaving workshop where cloth was dyed.
Ancient people may have gotten the idea to dye fabrics when they noticed stains on their clothing after eating or working with different plants, berries, and mollasks (Salzberg 3). They began to use these plants and animals to dye fabrics.
Ancient dyes can be classified chemically into three groups: blue and purple indigoid vat dyes, red anthraquinonoid mordant dyes, and yellow flavonoid dyes (Koren Historico).
As seen in Table 1, blue indigoid vat dyes were extracted from indigo plants. Purple vat dyes were extracted by the Phoenicians from secretions of a local mollusk. Since only a tiny amount of dye came from a single mollusk, huge quantities were harvested (12,000 mollusks for 1.5 grams of dye) (Orna Coordination 168). Because such large quantities of mollusks were harvested, the Phoenician city of Tyre had an extremely foul odor from rotting mollusks. Because the process of extracting the purple dye was so costly, only very wealthy people could afford to purchase purple cloth. Purple therefore became the color of royalty, and the dye is sometimes called "royal purple" (Salzberg 3).
Indigo and royal purple are classified as vat dyes because they had to be chemically converted before they could be used. When extracted from the indigo plant or mollusk, the indigoid dyes were not soluble in water, so they could not be applied to fabric. Ancient artisans first reacted the dyes with an alkaline solution made from wood ash, plant ash, lime, or stale urine to produce the water-soluble salt. They dissolved the water-soluble salt in water, and the fabric was soaked in the solution. Once the garment was exposed to air to dry, the dye oxidized back to the deep blue compound that was not soluble in water, so it would not wash out of the fabric (Koren Historico 273).
As seen in Table 2, red anthraquinonoid mordant dyes came from henna and madder. These dyes were water-soluble, so they ran and washed out of fabric unless a mordant was added to fix the dyes. The mordant reacted with the dye to produce a "lake," which was a large chemical complex that was not soluble in water.
As early as 1000 BC, people began to use potassium alum mordants (K(Al(SO4).12H2O) (Salzberg 3). The aluminum ion from the mordant formed a large complex with madder that was brick-red in color and would not wash out of fabrics (Cronyn 286). By using different mordants of chromium, tin, and iron salts, ancient dyemakers could make chocolate-purple and pink complexes (Orna Coordination 175). Acidic mordants, such as tannic acid (gallotannic acid) were also used (Koren Historico 272).
As seen in Table 3, yellow flavonoid dyes came from weld and safflower yellow. These dyes were applied directly to fabric without the use of mordants. For this reason, they are classified as "direct dyes" (Koren Colorful Natural History).
Dr. Zvi Koren, a chemist at the Edelstein Center, uses high performance liquid chromatography (HPLC) to analyze dyes in ancient fabrics. To extract indigoid dyes, Koren adds a piece of the dyed fabric to N,N-dimethylformamide (DMF) and heats it to 150°C, which is just 3 degrees below the boiling point of DMF. He filters this solution and then washes the fabric with hot DMF two more times. He combines these washings with the extract and injects it into the HPCL where the purple colors are separated.
To extract mordant and direct dyes from a fabric, Koren puts a small piece of fabric into 3M HCl. The HCl breaks the mordant dye to mordant-ion bond. Then he adds methanol to extract the dye from the fabric. He removes the fabric from the solution that now contains most of the dye, and evaporates off the HCl and methanol. Then he dissolves the residue in DMF and filters the solution. He injects the filtrate into the HPLC where the colors are separated by chromatography. Koren then compares the chromatograph to chromatographs of known dyes to determine the makeup of the ancient dyes (Koren Historico).
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Orna, Mary Virginia, Adrienne W. Kozlowski, Andrea Baskinger, and Tara Adams. "Coordination Chemistry of Pigments and Dyes of Historical Interest." American Chemical Society, 1994.
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Orna, Mary Virginia. Personal interview. 6 Dec. 1999.
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