The greater number of red shades are now dyed by means of the artificial dye-stuffs, as these are much easier to dye than are the natural dyes, and they give, on the whole, more even and brilliant shades, while as regards fastness to milling, acids, and light they are fully equal, and in most cases superior, to the natural dyes.
The Direct Red Dyes.--Of this group of red dye-stuffs, Benzopurpurine, Titan Scarlet, Diamine Fast Red F, and Benzo Fast Red are types; many of them have been found to be very serviceable in wool dyeing. They may be dyed either from plain baths containing common salt or Glauber's salt, or from baths containing common salt or Glauber's salt and a little acetic acid.
Alkaline or soap baths do not work well as a rule, and must be avoided in wool dyeing. Generally the dye-bath is exhausted of colour, and full shades are easily obtained, while these reds are in general remarkable for the evenness and uniformity of tint which can be produced. The reds so dyed are, on the whole, fairly fast to soaping, and can be used for dyeing goods that have to be milled, while their resistance to light and air is fairly good. Benzopurpurine and Diamine Red are more or less affected by acids, but the Titan Red and some of the more modern reds, Diamine Brilliant Scarlet, Benzo Fast Scarlets, are all fast to acids. The fastness to washing and light of some of them, Benzo Fast Red, Diamine Fast Red F, Titan Red, is much increased by adding, after the wool has been dyed, 3 per cent. of fluoride of chromium to the dye-bath, and working a little longer.
The dyeing with these colours is done at the boil, and the goods may be entered direct into the boiling bath without fear of uneven shades being produced. This bath may be kept as a standing one, simply adding as each lot is dyed the necessary quantity of dye-stuff, a little fresh water to bring the bath up to its original volume, and a corresponding quantity of the salt originally added. The wool can then be entered and dyed.
In place of using salt or Glauber's salt, acetate of ammonia is an excellent assistant for this class of dyes.
The following are some recipes for dyeing various shades of red on wool with this class of dyes.
Scarlet.--The dye-bath is made with 3 lb. Titan Scarlet C B, and 10 lb. acetate of ammonia. This gives a good bright shade of scarlet, which is fast to acids and soaping, although not fast to light.
Scarlet.--Dye in a bath made with 3 lb. Diamine Scarlet B and 10 lb. Glauber's salt. This yields a light shade, not so fast to acids as the last, but equally fast to soaping and light.
Scarlet.--Make the dye-bath with 3 lb. Benzopurpurine 4 B, and 10 lb. Glauber's salt. This also gives a good shade of Scarlet fast to soaping. It is turned dark blue by acids, and is not fast to light. It is very largely used on underwear goods, but is not so satisfactory for this as the Titan Scarlet C B, or Benzo Fast Scarlet B S.
Scarlet.--The dye-bath may be made with 3 lb. Brilliant Congo G, 10 lb. Glauber's salt and 2 lb. acetate of ammonia. This gives a satisfactory shade of scarlet.