The leather is run in the dyestuff solution at a temperature of about 45° to 50° C. for about half an hour, and then lightly fat-liquored, if desired, and afterwards dried.

In addition to the dyestuffs mentioned above many basic colours may be employed after the treatment with titanium, some of these producing a colour lake with the titanium mordants.

As regards the permanency of the various colours to light, the reader is referred to an important paper by Mr. Lamb,[199] but in many cases the probable permanency is indicated by a number prefixed to the name of the colour in Roman figures, I. corresponding to the lowest, and X. to the highest permanency. In the research referred to, about 1500 samples of leathers dyed with coal-tar dyes were exposed to light for a series of “periods,” each equal in actinic power to nine days of the brightest summer sunshine. The most fugitive colours faded completely, even in the first “period,” and the most permanent before the end of the tenth. The prefixed numerals indicate to which of these “periods” the colour survived.

[199] Journal of Society of Chemical Industry, 1902, p. 156.

INDEX.