The letter or letters, following the name, refer generally to the shade, as for instance, B for blue, R for red, Y or G for yellow (German _gelb_), and so on. Thus “methyl violet” is sold in brands running all the way from 6 B to 6 R—that is, from full purple shades that are very close to blue, to bright violet shades, very close to red. Sometimes, however, the letter refers to the composition of the dye or its class, as “fuchsine S” (German _sauer_) often called acid fuchsine or acid magenta; or “alizarine blue, D,” when the D indicates a “direct” cotton color. And sometimes the letter F is used to indicate fastness to light, in which case “F F” would signify a brand of very unusual fastness, for that particular class of colors at any rate. But not infrequently the letter is merely a mark applied for purposes of identification, whose significance cannot easily be learned by those not in the business of color selling, even when it is not a secret closely guarded by the particular firm supplying the dyestuff. For this reason, the name of the manufacturer or agent should _always_ be added to the color name and letter, if it is important to get a particular color in any case. The best of the older dyes are manufactured by all of the larger firms, of substantially the same strength and shades, although often not under the same names. The later colors, whose patents have not expired, are of course the individual property of the different manufacturers, and can be, and are, marketed by them under any name they like to give them. Accordingly it frequently happens that two different firms may sell, under the same name, two entirely different colors; it would be impossible to tell which dyestuff was intended unless the firm name were attached. But with these three essentials correctly given—name, brand, and maker—a color can be identified and obtained true in composition and shade, even after the lapse of many years. CLASSIFICATION OF THE COAL-TAR COLORS AVAILABLE FOR CRAFTSMEN.