The principle of alkaline mordants is not a strictly new one. If it be remembered that the old killing formulas used by the fur dyers of an earlier age, contained metallic salts with mordanting properties in addition to the alkaline substances, which alone were effective as killing agents, it would seem that the suggested alkaline mordants were merely a revival in modified form of the old processes. This is undoubtedly true in a large measure, for the killing mixtures which the old masters used certainly embodied the fundamental principle of simultaneous killing and mordanting, although it was not recognized at that time.
Modern alkaline mordants have therefore been devised which can be employed for killing and mordanting furs at the same time. They are prepared as follows:
250 grams of potassium alum are dissolved in 1 liter of boiling water. To this solution is added 300 grams of soda ash, previously dissolved in 750 c.c. of water, and the resulting precipitate is filtered off, washed and pressed, and then dissolved in a solution of 65 grams of caustic soda in 1 liter of water.
250 c.c. of chrome acetate mordant of 20 degrees Beaumé 320 c.c. of caustic soda solution of 38 degrees Beaumé (32.5%) 10 c.c. of glycerine 30 degrees Beaumé (95%)
The solution of these substances is brought up to a volume of 1 liter by the addition of 420 c.c. of water.
138 grams ferrous sulphate are dissolved in 362 c.c. of warm water. Cool and add 25 c.c. of glycerine. Then slowly and carefully add 25.5 c.c. of concentrated ammonia, taking care that no precipitate forms.
While these alkaline mordants seem to have much in their favor, there are certain possible objectionable features which must be considered. The solutions of the mordants are generally very alkaline, and not every fur can withstand more than a limited quantity of alkaline substance for longer than a comparatively short time. Suitable mordanting usually requires a longer time than killing does, so with the use of the alkaline mordant, if the skins remain in the solution until sufficiently killed, they may be insufficiently mordanted, while if the furs are treated long enough to be properly mordanted, the hair may have been over-killed. However, the idea of the alkaline mordant is a good one, and it is only a matter of time and patient, scientific experimentation when the difficulties of the method will be eliminated, and a much-desired process will become a practical realization.