Fur dyes of American make being equal in every way to the German product, show the same color reactions with the various mordants. The following table shows the shades produced with the same mordants as above: ========================================================================= | CHROME | COPPER | IRON | DIRECT ---------+---------------+---------------+---------------+--------------- Rodol D | brown black | coal black | coal black | brownish black Rodol P | red brown | dark brown | grey brown | light brown Rodol 2G | yellow brown | yellow brown | yellow brown | dull yellow Rodol 4G | light brown | light brown | reddish brown | pure yellow Rodol A | ... | blue black | ... | blue black Rodol | | | | Grey B | greenish grey | greenish grey | mouse grey | ... Rodol | | | | Grey R | greenish grey | brownish grey | mouse grey | ... ---------+---------------+---------------+---------------+--------------- All these shades are produced by dyeing in a bath containing a _neutral_ solution of the dye. Sometimes the dye comes in the form of a salt of a mineral acid, like hydrochloric or sulphuric acid, in which case a sufficient amount of an alkali, usually ammonia, is added to liberate the free base. According to the Cassella Co., German manufacturers of the Furrol brand of fur dyes, the dyeing can also be carried on in slightly alkaline or in slightly acid solution, a different series of shades being obtained in each instance. Ammonia is used to render the bath alkaline, and formic acid to make it acid. The most customary practise, however, is to use neutral solutions of the dyes. For preparing the mordant solutions much smaller quantities of the metallic compounds are used than in the case of the vegetable dyes. With chrome mordants cream of tartar is always employed as an assistant, and occasionally also with copper and with iron mordants. With copper, and also with iron mordants no addition is made at all, or sometimes a small quantity of acetic acid is added. The temperature of the mordant solution is kept about 30° C., and the duration of the mordanting varies from 2–24 hours according to the depth of shade desired. The concentration of the solution may also be varied, it sometimes being just as well to use a strong mordant solution and less duration of mordanting. Chrome may be combined with copper, and iron may be combined with copper, but chrome and iron do not go together as mordants. Some typical average mordanting formulas are as follows: Chrome mordant. Bichromate of soda 2.5 gms. Cream of tartar 1.5 gms. Water 1 liter Copper mordant. Copper sulphate 2 gms. (Acetic acid 50% 2 gms.) Water 1 liter