Page:Natural History, Mollusca.djvu/51

 mantle, a thick vein of a yellowish white hue, filled with a substance resembling cream: this is the dye in question. It is thick and glutinous, so that you cannot well apply it with a pen; but with a camel's-hair pencil you may paint, as it were, upon linen or cotton cloth any lines, the initials of your name, for example. When you have done this you will perhaps be disappointed, for the marks as they dry will be but just discernible, displaying only a pale yellow tint with not the slightest approach to purple, but exhaling an insufferable odour of garlic.

Place your linen in the light of the sun, and look at it again in half-an-hour, or, if you please, watch its changes. The marks have by this time passed from yellow into pea-green, and are now of a full grass-green; under the influence of the light the change proceeds rapidly, the yellow element gradually disappearing, and the blue element becoming more and more prominent, until through the stages of deep-green, sea-green, and greenish-blue, the colour at length appears a full indigo. The red element now begins to be apparent, and rapidly increases in intensity until the hue is a dull, reddish purple. In my own experiments this was the ultimate tint obtained; a tint perfectly indelible as long as the texture of the material remained, neither light, nor time, nor washing, nor the application of chemical agents having now the least influence either in changing its hue or causing it to fade. I have seen it stated that if the cloth be washed in scalding water and soap, it comes out from the lather changed from the reddish purple hue to a fair bright crimson; with me, however, the soap and the hot water had no appreciable