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Napoleon's Case

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Napoleon's Buttons- Chapter 9 - Dyes

1.Why were indigo and Tyrian purple so valued?How were they obtained?

Indigo and Tyrian were valued because they were expensive, regarded as royal colors, and produced by very labor-intensive methods. Since most of mans earliest colors were plant based, there were not many plants that produced blue shades. Only one plant, Indigofera tinctoria, contained the blue pigments necessary for the indigo shade. Tyrian purple was valued as in some cultures, only royalty was able to wear the color purple.

The leaves of indigo-producing plants are fermented under alkaline conditions followed by oxidation. Indigo was obtained by leaves from the plants being left to either soak in urine or get covered by ashes, which fermented them. When oxygen from air was added, the resulting color was blue. Tyrian purple was obtained from the opaque mucus secreted by mollusks or snails. In fact, it took nine thousand shellfish to produce one gram of Tyrian purple. Oxidation by air is what caused the color to develop

2.What seems to be the common chemical reaction that the precursors of dyes undergo to develop their color?


3.What chemical feature gives dyes their color properties?

Glucose units that are attached to the color producing molecule oxidize. As the dyes oxidize, the color becomes visible.

Double bonds alternating with single bonds which allow light to reflect so the color can be seen. This is referred to as conjugation. The absorption of different wavelengths of visible light allows us to see the colors.

4.What is a mordant dye?How does the mordant chemical change the color?

A mordant dye is a natural dye where a metal ion is added to fix the color to fabric. In order to change the colors on fabric, different metal salt solutions are added to the fabric before dying. A mordant dye makes the color last longer, instead of bleeding out at every wash. Adding aluminum gives a rose-red color and magnesium gives a violet color.

5.What is the structure of anthraquinone?What is its significance to dyes?

(Anthraquinone structure, 2013)

Anthraquinone is the parent compound of a number of naturally occurring dyes.

It is the colorless version where once oxidized, the color becomes apparent. The alcohol groups and single and double bonds in the rings are what give the ability to absorb light. The location and numbers of the OH groups on the rings and carbon chains are what give the different colors.



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