Dyes

            

          If we lived in a world in black and white it would be a sad and depressed world, because color is 

what gives fun and liveliness to life. Color brightens everything and everyone and because of that the love for dies is understandable. A substance that is able to give life to the most boring fabrics and objects will always be a treasured substance. 

            The discovery and exploitation of dyes goes back thousands of years with natural or man-made molecules which have created and developed the biggest chemical companies in the world today. The early dyes were not very good, having many flaws to it since the color would not stick to the fabrics fibers, and would eventually wash off, but it is believed that this early manipulation of dyes obtained from plants were some of the first attempts in the practice of chemistry.  One of the rare dyes in the past was blue indigo obtained with the leaves from Indigofera tinctoria, which after fermentation in alkaline conditions and oxidation would turn blue. This phenomenon occurred due to the indican molecule attached to a glucose that was found in this plant. The indicant would separate from the glucose due to the alkaline conditions and form indoxol, which reacting with oxygen would produce indigo, source of the blue color. Indigo was one of the most valuable dyes, but a dye named Tyrian purple was even more rare and precious, and thought as the imperial color. This dye is a dibromo derivative of indigo, and was obtained from marine mollusks or snails which secreted a compound which after oxidation would develop the compound that produced the valuable Tyrian color.

            Dyes are able to give color thanks to its molecules ability to absorb certain wavelengths of light from the visible spectrum. The color we see will then depend on the wavelengths absorbed by the die, if the wavelength of red light is absorbed the complementary color green will be reflected. If no wavelengths are absorbed the color will be white, and if all wavelengths are absorbed it will produce black color. For the wavelength absorbed to be in the visible range there must be an alternation of double and single bonds which are referred as conjugated bonds. The fact that indican doesn’t produce a strong color is due to the fact that it doesn’t have enough conjugation. However indigo molecule have twice the number of conjugated bonds and also have oxygen atoms as part of the conjugation making this molecule highly colored.

            In France by the end of the eighteenth century dye industry had become one of the most important sources of wealth of the country and the government subsidies may have started with the dye industry. One color that was use in the French military by norm, was Turkey red which gave a beautiful strong tone of red. This color is produced by the Alizarin molecule, a derivative of anthraquinone which is colorless due to the lack of conjugation. This conjugation is found in the derivative since it has two OH groups, and this conjugation makes it possible for the molecule to absorb visible light. OH groups may be very important for the color reflected by a molecule because the change in its position can change the molecule and the color it produces.

            Other primary dyes like cochineal and kermesic acid were obtained from animals, the first one being very expensive and obtained from insect’s bodies. And the second one also from the body of another insect named kermes insect which produced a bright red color usually used on women’s lips. As for the primary color yellow, this was obtained from the saffron crocus which had the molecule named crocein. The use of saffron as a dye declined and now is used as a flavoring substance for food and one of the most expensive spices.

            Starting in the late 1700’s the first synthetic dyes started to be produced and like this an man-man dye industry slowly started taken the place of the natural dyes industry that had lasted for millennium. The first dye to be synthesized was pitric acid, which produced a strong yellow color, however being a nitro compound this substance was very unpredictable and had the potential to spontaneously explode. In the following years synthetic alizarin and indigo had also been produced, and synthetic indigo is very familiar to us since it is still today the dye used to coloring jeans. However the synthetic dye that took the world by storm and changed the dye industry was found by Henry Perkin and was named mauve. This dye which produces a brilliant lavender purple, was accidently discovered, but was on the most important discoveries in fashion. Important people started to love and wear this color, and this period was even named the mauve decade. Perkin’s obtained this dye from the coal tar residues and to this day the molecule mauveine, responsible for the color mauve, is still somewhat of a mystery since the materials isolated by Perkin’s were not pure and the color produced came with the mixture of other compounds.

            Through history so many different dyes were manipulated and produced, even during times when science and knowledge about chemistry was not that vast the dye manipulation was still a big industry that created a lot of changes in the world. The authors have shown the reader all the various types of dyes developed and how they work, and the various countries and companies that gained wealth due to this valuable industry. Dyes are still important today, even though natural dyes have almost been completely substituted by synthetic ones, dyes are still used in all the things around us. All the objects we have around us have color, and that is all due to the dyes used on it. The happiness color gives in our daily life is all thanks to the dyes that started to be produced by our ancestors.