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The Secret of Everyday Things by  Jean Henri Fabre


 

 

DYEING AND PRINTING

[64]

"A
RRIVED at this point, the cotton cloth is ready to receive the colors. This operation involves the use of means so varied and technical knowledge so above your understanding that I should not be understood if I undertook to enter into some of the more elaborate details."

"I supposed, on the contrary," said Claire, "that it was a very simple thing and that the colors were put on the cloth with a paint-brush just as I should do, though not very well, on a sheet of paper."

"Undeceive yourself, my dear child: the paint-brush has nothing to do with printed cottons, nor yet with the other kinds of goods embellished with colors. Done with a paint-brush, the designs would not be lasting, but would disappear with the first washing. The slightest rain would make the colors run and would turn them into horrible shapeless blots. To resist water, and sometimes vigorous washing with soap, the colors must penetrate the fabric thoroughly and become embodied in it.

"Let us see how this result is arrived at, taking black for an example. This color is obtained in various ways, notably with ink, the same that we use for writing. Well, if we immersed a strip of white material in this liquid it would come out black, [65] but the color would have no staying power. A little rinsing in water would remove most of the ink, and the small amount remaining would give only a pale tint, very insufficient and soon washed out. In order to give a deep and lasting black the ink, when it is applied to the fabric, must be in an unfinished state, and it must finish itself in the cloth; the ingredients of which it is composed must mingle and become ink in the very substance of the threads. Under these conditions the black, made on the spot and permeating the minutest fibers of the cotton, acquires all the desired fixity and intensity. Let us, then, before going further, examine the ingredients of which ink is composed.

"There are found growing on oak-trees certain globular formations of about the size of a billiard ball and with the appearance of fruit. But they are not really fruit; they have nothing in common with acorns, the real fruit of the oak. They are excrescences caused by the sting of a tiny insect known as the gall-fly. This insect stings the leaf or tender twig with a fine gimlet that arms the tip-end of its stomach, and in the microscopic incision it deposits an egg. Around this egg the sap of the tree gathers, finally forming a little ball which by degrees becomes as hard as wood. The insect hatched from the egg develops and grows in the very heart of this ball, whose substance serves [66] it as food. When it has grown strong enough it pierces the wall of its abode with a small round hole through which it escapes. That is why you see most of these balls pierced with a hole when they fall to the ground toward the end of autumn. These round excrescences are called gallnuts or oak-apples, and they furnish one of the ingredients of ink, one of the materials used for dyeing black.


[Illustration]

GALL-FLY

"The other ingredient is green copperas. At the druggist's you may have seen a substance looking something like broken glass of a light green color with spots of rust. That is green copperas. It is obtained by dissolving iron in an excessively corrosive liquid known as oil of vitriol or sulphuric acid. This terrible liquid, so dangerous in inexperienced hands, dissolved iron as easily as water dissolved salt or sugar; and in this solution, after a certain time, crystals are formed. It is this crystallization that give us our green copperas, a substance having none of the dangerous qualities of the oil of vitriol used in making it, but one that can be handled without the least risk, though its taste is most disagreeably tart. This substance dissolves very readily in water.

"That is all that is needed for making ink. Let us boil a handful of pounded gallnuts in water; we shall obtain a pale yellowish liquid. Also, let us dissolve some copperas in water, and the latter will turn a very pale green with a yellowish tinge. What will happen on mixing the two liquids, one yellow and the other green? Nothing very remarkable, it would seem. And yet no sooner do these two liquids [67] mingle than there is produced a deep black, the very color of ink."

"And so the ink comes all of a sudden." said Maria.

"Yes, the very instant the gallnuts and the copperas meet in the water that holds them in solution. If ink for writing is desired, however, a little different method must be followed so as not to have an excess of water, which would weaken the color. To the liquid resulting from boiling the gallnuts there would simply be added the undissolved copperas with a little gum to give brilliance to the ink. I have gone out of my way in describing to you this mingling of two liquids in order to show you the more clearly how the union of two substances, each having little or no color, can produce a color totally unlike either of the original shades. From two liquids, one a pale yellow, the other a pale green, you have just seen ink spring into being with startling suddenness. Remember this phenomenon, for it will explain certain results of dyeing that are very astonishing to the uninitiated. Bear in mind that sometimes perfectly colorless substances can produce magnificent colors by being united.

"Now that we know how ink is made, let us return to the subject of dyeing black. We put a piece of percale to soak in water in which gallnuts have been boiled; then, when it is well saturated, we take it out and dry it. What, now, will be its color!"

"It will be the color of the gallnut water," answered Claire; "that is to say, a pale and dirty yellow."

[68] "Right; but if the fabric thus saturated is dipped into a solution of copperas, what will happen?"

"That is not hard to guess," was the reply. "The copperas, finding gallnut dye on the surface and in the texture of the cloth, all through it in fact, will immediately form ink, which will color the percale black."

"And more than that," added Marie, "the dye will penetrate the goods evenly in every part, since the saturation with gallnut water extends to the very tiniest thread of the material."

"Yes; and so you see that in this way the black dye is formed on the spot, in the very heart of the cotton threads. Thus we obtain a fast color, all the necessary conditions being complied with.

"A great many other colors—red, violet, brown, yellow, lilac, no matter what—are produced in similar fashion. First the material to be dyed is saturated with a solution that will develop the desired color, or make it spring into existence, on encountering another solution, and will set the color by making it one with the fabric itself. This preparatory substance which in a second operation is to mix with the dyestuff so as to develop and fix the color is called the mordant and varies in kind according to the tint desired, so that by changing the mordant different colors may be obtained with one and the same coloring matter."

"In the same way you have just explained to us," said Marie, "we get cloth dyed all one color. I should like to know how patterns of several colors on a white ground are made."

[69] "That is done by printing or stamping. Imagine a small wooden block or board on which is engraved in relief the design to be reproduced. Clever engravers skilled in all the details of ornamental design prepare these blocks, which are sometimes veritable masterpieces of art; and it is these that constitute the calico-printer's all-important equipment.

"To take a simple example, let us suppose the workman proposes to put a black design on a white ground. On a large table in front of him he has the piece of percale which unrolls as he needs it; in his right hand he holds the printing-block. The engraved design, which stands out in relief, he moistens slightly with a fine solution of gallnuts, and then applies the block to the goods. The parts thus touched are the only ones impregnated with this preparation, the rest of the percale remaining as it was before. He continues thus, each time dipping the engraved face of the block into the gallnut preparation, until the piece of cloth has received the impression throughout its entire length.

"That done, all that is necessary is to dip the goods into a solution of copperas to make the design appear in black, since the ink forms wherever the wooden mold has left a deposit of gallnut water, all other parts remaining white."

"It is simpler than I had thought," said Claire, "and much simpler than using a paint-brush, as I supposed at first must be the way."

"The operation can be made still simpler. As a rule the coloring matter and the mordant, that is to say the substance that brings out the color and fixes [70] it, act only under the influence of the heat. Accordingly, the process is as follows. The two ingredients, mordant and coloring matter, are mixed together and reduced to a fine pap with which the engraved surface of the block is moistened and then immediately applied to the fabric. The preparation thus deposited gives only one color, one alone, determined by the nature of the mordant and the coloring matter. If the design is to be multicolored, as many blocks must be used as there are tints, each block representing only the part of the design having the color it is to imprint on the goods. Thus the piece of percale passes through the workman's hands once for red, again for black, a third time for violet, in fact as many times as there are colors in the design, however little they may differ from one another."

"It must be a very delicate piece of work," remarked Marie, "to put the different parts of the design exactly in the right place so as to get from them all a pattern with the various colors joining perfectly and never overlapping."

"The calico-printer's skill makes light of this difficulty. The design comes out as clear as a painter could make it with his brushes. To complete the description in a few words, when all the colors have been applied, the fabric is removed to a closed room where it receives a steam bath. Heat and moisture aiding, each dye mixes with its mordant, which incorporates it with the fabric, and beautiful bright tints spring forth as by enchantment where the engraved blocks had left only a sorry-looking daub."


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