420

DYEING.

forms, with the brown yellow of the goods, a mixture tending to white, or less coloredthan the yellow of the goods and the blue together were. For the same reason, a mix-ture of Prussian blue and cochineal pink has been of late years used in the whitening orthe azuring of silks, in preference to a pure blue; for on examining closely the color oithe silk to be neutralized, it was found by the relations of the complementary colors, thatthe violet was more suitable than the indigo blue formerly used. The dyer should know,that when he applies several different coloring matters to stuffs, as yellow and blue, forexample, if they appear green, it is because the eye cannot distinguish the points whichreflect the yellow from those which reflect the blue; and that, consequently, it is onlywhere the distinction is not possible, that a mixture or combination appears. WJen weexamine certain gray substances, such as hairs, feathers, &c., with the microscope, wesee that the gray color results from black points disseminated over a colorless or slightlycolored surface. In reference to compound colors, this instrument might be used withadvantage by the dyer.

The dyer should be acquainted also with the law of the simultaneous contrast ofcolors. When the eye views two colors close alongside of each other, it sees themdiffering most in their optical composition, and in the height of their tone, when the twoare not equally pale or full-bodied. They appear most different as to their optical com-position, when the complementary of the one of them is added to the color of the other.Thus, put a green zone alongside of an orange zone; the red color complementary ofgreen, being added to the orange, will make it appear redder; and in like manner theblue, complementary of orange, being added to the green, will make it appear more in-tensely blue. In order to appreciate these differences, let us take two green stripes andtwo orange stripes, placing one of the green stripes near one of the orange: then placethe two others so that the green stripe may be at a distance from the other green stripe,but on the same side, and the orange at a distance from the other orange, also on thesame side.

As to the contrast in the height of the tone, we may satisfy ourselves by taking thetones No. 1, No. 2, No. 15, and No. 16, from a graduated pallet of reds: for example?by placing No. 2 and No. 15 close alongside, putting No. 1 at a distance from No. 2on the same side, and No. 16 at a distance from No. 15 on the same side,—we shaljsee (if the pallet is sufficiently lowered in tone) No. 2 equal to No. 1, and No. I 3equal to No. 16; whence it follows that No. 2, by the vicinity of No. 15, will appearto have lost some of its color; while No. 15 will appear to have acquired color. Wh enblack or gray figures are printed upon colored grounds, these figures are of the colorcomplementary of the ground. Consequently, in order to judge of their color, we mustcut out spaces in a piece of gray or white paper, so as to allow the eye to see nothingbut the figures; and if we wish to compare figures of the same color, applied upongrounds of different colors, we can judge rightly of the figures only by insulating themfrom the grounds.

The relations of dyeing with the principles of chemistry, constitute the theory of th®art, properly speaking; this theory has for its basis, the knowledge—1. of the species oibodies which dyeing processes bring into contact ; 2. of the circumstances in which thesespecies act; 3. of the phenomena which appear during their action ; and 4. of the p*'°P'erties of the colored combinations which are produced. These generalities may be spec 1• fled under the ten following heads :— , r

1. The preparation of the stuffs to be dyed, whether fibres, yarn, or cloth; unthe heads of ligneous matter, cotton, hemp, flax; and of the animal matters, silk awool.

t 2. The mutual action of these stuffs, and simple bodies.

♦ 3. The mutual action of these stuffs, and acids.

4. The mutual action of these stuffs, and salifiable bases, as alumina, &c.

5. The mutual action of these stuffs, and salts.

6. The mutual action of these stuffs, and neutral compounds not saline.

7. The mutual action of these stuffs, and of one or more definite compounds.

8. Of dyed stuff's considered in reference to the fastness of their color, underfluence of heat, light, water, oxygen, air, boilings with soap, and reagents.

9. Of dyeing, considered in its connexions with chemistry. .. a nd

10. Of dyeing, considered in its relations with caloric, mechanics, hydrau i ?optics.

1. The preparation of stuffs. se pa-

The operations to which stuffs are subjected before dyeing, are intended—!- ‘ therate from them any foreign matters; 2. to render them more apt to unite a

coloring tinctures which the dyer proposes to fix upon them, in order to giv ^ goilel imore agreeable, or more brilliant aspect, or to lessen their tendency to assuro e eitherappearance by use, which white surfaces so.readily do. The foreign mnU®* Qr ot hernaturally inherent in the stuifs, or added to them in the spinning, weaving