The first efforts in this direction were based upon the saving of some or, indeed, nearly all, of the gum which is wasted in the stripping or degumming process previously described. This gum, which amounts to from 20 to 35 per cent. of the raw silk, makes the silk stiff in texture and dull in color and more difficult to dye. Accordingly, in former years, it was invariably washed out of the silk with the greatest care before any attempt was made to dye it. But by modifying the dyeing, and especially the finishing process, it was found possible to produce the so-called “souples”—i.e., silks with little or no lustre, but with the characteristic “scroop” or “feel”—capable of replacing bright silk as a filling in many fabrics and yet containing almost all the natural gum left in the fibre. The black silks were then attacked and an elaborate system of mordanting was introduced before the dyeing proper began. For instance, the silk can be steeped alternately in one solution after another, first of iron salts and then of ferrocyanide of potash, thus forming Prussian blue in the fibre. Then the excess of iron can be converted by immersion in tannin solutions, such as Gambier or Cutch, into black tannate of iron, or ink, and finally, after perhaps a light bath in chromium salts, the real black color is brought out by boiling in logwood extract. The silk is then brightened by boiling with good neutral Castile soap, is shaded, if necessary, by dyeing with either an Acid or Basic dye in a weak bath, and, after drying and finishing, the finished product may easily weigh two or even three times as much as the original raw silk, and still retain its strength, lustre, and elasticity. _Tin Weighting._—The weighting of colored and bright silks did not proceed so rapidly, and it was not much more than ten years ago that, by accident, some French dyers discovered that by immersion in a strong bath of tin chloride (stannic chloride acidified with some hydrochloric acid) the silk fibre would absorb a large percentage of tin salts without necessarily losing lustre, dyeing capacity, or even strength. This at first was kept a secret, but its use gradually spread, until now it is a very poor silk dyer who cannot weight his silk 100 or 150 per cent. without spoiling its immediate commercial value. Without going into unnecessary details, the process is somewhat as follows: The silk, after being degummed and thoroughly washed free of soap, is plunged into a bath of tin chloride and kept there for some hours. It is then taken out and the loose tin salts are washed off in a tank of water (technically called a box), or in a washing machine. To further “set” the tin, the silk is then placed for a short time in a solution of phosphate of soda and again washed thoroughly. It has now gained from 15 to 25 per cent of its original weight (2½ to 4 ounces to the pound of raw silk).