Another attraction is the feeling of working all the time in an unexplored or very partially explored country. There is the constant chance of obtaining at any moment effects never thought of before. The experimenter is always trying some new little trick in tying, or in folding, or in dyeing, the results of which can never be foreseen accurately, and which are always interesting and often very beautiful.
Tied and Discharged Work.—One day, in our laboratory, some experiments were made which resulted in a modification of this process which, so far as we know, was entirely new, and which presents very interesting possibilities, to say the least. We made the experiment of dyeing the cloth first, and then tying it up, and putting it in a bleaching solution, so as to discharge the color everywhere excepting where it was protected by the tying. The experiment was successful, resulting (see Plate IV, Fig. [b]), in a series of dark patterns on a light background. All kinds of modifications of this can be made. For instance, the cloth can be dyed with a mixture of two or three dyes, some of which are fast and the other or others can be discharged by the chemical used. The pattern thus will be the full mixed color, say brown, against a background of red or yellow or blue as the case may be.
| FIG. 11—CENTRE AND CORNERS TIED | FIG. 12—DYED, UNTIED AND SHAKEN OUT |
The important thing about this modification is to select the proper bleaching agent to act on the particular colors, and the particular kind of material, used. Our first experiments were with bleaching powder (chloride of lime), dissolved in water, say two tablespoonfuls to the gallon, with, if necessary, a few drops of acetic acid or weak sulphuric acid stirred into it. This powerful bleaching agent is very apt to attack the cloth, and only heavy materials, such as scrim or heavy calico should be used with it. But although so strong, it does not act at all readily on a large number of the dyestuffs, including many of the Vat colors. Some of these, like the Indanthrene colors, are not affected at all, Indigo is changed from blue to a brilliant shade of yellow. And Thio Indigo Red B produces curious shades of purple, settling, where exposed to the full action of the bleaching agent, to orange.
Later we repeated the experiments, using hydrosulphite of soda, say two tablespoonfuls to the gallon of warm water, as a discharge, with much better success. The cloth was not injured, even when delicate materials like silk and light poplins were used. And the great majority of colors, including nearly all the best Salt, Sulphur, and Acid dyes, reduced rapidly and well. The Vat dyes will reduce, and, in the presence of caustic soda, will dissolve out of the exposed cloth almost entirely, but it is hard to reduce them to white in this way. In every case the color, after reduction, must be washed at once in warm soap and water, or else, on exposure to the air, the color may come back to some extent, owing to oxidation.
A weak bath of hydrosulphite of soda, also, should always be on hand, in the former bleaching process; for, when bleaching powder (chloride of lime) or other chlorine compounds, such as Javelle water or Labarraque’s solution, are used for destroying the color, their further action can be stopped, and also the offensive smell removed, by dipping the bleached material into a so-called antichlor, like this hydrosulphite.
This subject of discharge is dealt with more at length in a future chapter.
(a) EXAMPLE OF TIED AND DYED WORK