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| | dye. The Columbia Encyclopedia, Sixth Edition. 2001-05 |
 | | Natural dyes are so called because they are obtained from plants (e.g., alizarin, catechu, indigo, and logwood), from animals (e.g., cochineal, kermes, and Tyrian purple), and from certain naturally occurring minerals (e.g., ocher and Prussian blue). |
 | | Dyes are classified also as acidic or basic according to the medium required in the dyeing process. |
 | | A vat dye, e.g., indigo, is so called from the method of its application; it is first treated chemically so that it becomes soluble and is then used for coloring materials bathed in a vat. |
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