13I shall now speak of purple, which, above all other colours, has a delightful effect, not less from its rarity than from its excellence. It is procured from the marine shell which yields the scarlet dye, and possesses qualities not less extraordinary than those of any other body whatever. It does not in all places where it is found possess the same quality of colour; but varies in that respect according to the sun’s course.
13I shall now begin to speak of purple, which exceeds all the colours that have so far been mentioned both in costliness and in the superiority of its delightful effect. It is obtained from a marine shellfish, from which is made the purple dye, which is as wonderful to the careful observer as anything else in nature; for it has not the same shade in all the places where it is found, but is naturally qualified by the course of the sun.