Tyrian purple 520 nm, which is green). It is believed that the intensity of the purple hue improved rather than faded as the dyed cloth aged. Vitruvius mentions the production of Tyrian purple from shellfish. In his "History of Animals", Aristotle described the shellfish from which Tyrian purple was obtained and the process of extracting the tissue that produced the dye. Pliny the Elder described the production of Tyrian purple in his "Natural History": The most favourable season for taking these [shellfish] is after the rising of the Dog-star, or else before spring; for when they have once discharged their waxy secretion,
Reactive dye Reactive dye In a reactive dye, a chromophore (an atom or group whose presence is responsible for the colour of a compound) contains a substituent that reacts with the substrate. Reactive dyes have good fastness properties owing to the bonding that occurs during dyeing. Reactive dyes are most commonly used in dyeing of cellulose like cotton or flax, but also wool is dyeable with reactive dyes. Reactive dyeing is the most important method for the coloration of cellulosic fibres. Reactive dyes can also be applied on wool and nylon; in the latter case they are applied under weakly acidic conditions.