CRAYONS

(Eng. and Fr.; Pastelstifte , Germ.) Slender, soft, and somewhat friable cylinders, variously coloured for delineating figures upon paper, usually called chalk drawings. Red, green, brown, and other coloured crayons, are made with fine pipe or china clay paste, intimately mixed with earthy or metallic pigments, or in general with body or surface colours, then moulded and dried. The brothers Joel, in Paris, employ as crayon cement the following composition: 6 parts of shell-lac, 4 parts of spirit of wine, 2 parts of turpentine, 12 parts of a colouring powder, such as Pru ian-blue, orpiment, white lead, vermillion, ., and 12 parts of blue clay. The clay being elutriated, pa ed through a hair sieve, and dried, is to be well incorporated by trituration with the solution of the shell-lac in the spirit of wine, the turpentine, and the pigment; and the doughy ma is to be pre ed in proper moulds, so as to acquire the desired shape. They are then dried by a stove heat. In order to make cylindrical crayons, a copper cylinder is employed, about 2 inches in diameter, and 1 1 ⁄ 2 inches long, open at one end, and closed at the other with a perforated plate, containing holes corresponding to the sizes of the crayons. The paste is introduced into the open end, and forced through the holes of the bottom by a piston moved by a strong pre . The vermicular pieces that pa through are cut to the proper lengths, and dried. As the quality of the crayons depends entirely upon the finene of the paste, mechanical means must be resorted to for effecting this object in the best manner. The following machine has been found to answer the purpose exceedingly well. IMG:4147767755307473660_illo0373b.png:Crayon machine Fig. 350. is a vertical section through the centre of the crayon mill. Fig. 351. is a view of the mill from above. A , the mill tub, whose bottom B must be a hard flat plate of cast iron; the sides A being of wood or iron at pleasure. In the centre of the bottom there is a pivot C , screwed into a socket cast upon the bottom, and which may be strengthened by two cro bars D , made fast to the frame E . F , the millstone of cast-iron, concave, whose diameter is considerably smaller than that of the ve el A ; it is furnished within with a circular basin of wood G , which receives the materials to be ground, and directs them to the holes H , which allow them to pa down between the under part of the muller, and the bottom of the tub, to undergo trituration. By the centrifugal motion, the paste is driven towards the sides of the ve el, rises over the sides of the muller, and comes again through the holes H , so as to be repeatedly subjected to the grinding operation. This millstone is mounted upon an upright shaft I , which receives rotatory motion from the bevel wheel work K , driven by the winch L . IMG:4147767755307473660_illo0373a.png:Crayon furnace The furnace in which some kinds of crayons, and especially the factitious blacklead pencils are baked, is represented in fig. 352. in a front elevation; and in fig. 353. , which is a vertical section through the middle of the chimney. A A , six tubes of greater or le size, according as the substance of the crayons is a better or worse conductor of heat. These tubes, into which the crayons intended for baking are to be put, traverse horizontally the laboratory B of the furnace, and are supported by two plates C , pierced with six square holes for covering the axes of the tubes A . These two plates are hung upon a common axis D ; one of them, with a ledge, shuts the cylindrical part of the furnace, as is shown in the figure. At the extremity of the bottom, the axis D is supported by an iron fork fixed in the brickwork; at the front it cro es the plate C , and lets through an end about 4 inches square to receive a key, by means of which the axis D may be turned round at pleasure, and thereby the two plates C , and the six tubes A , are thus exposed in succe ion to the action of the fire in an equal manner upon each of their sides. At the two extremities of the furnace are two chimnies E , for the purpose of diffusing the heat more equably over the body of the crayons. F , fig. 352. , is the door of the fire-place, by which the fuel is introduced; G , fig. 353. , the ash-pit; H , the fire-place; I , holes of the grate which separate the fire-place from the ash-pit; K , brickwork exterior to the furnace. General Lomet proposes the following composition for red crayons. He takes the softest hematite, grinds it upon a porphyry slab; and then carefully elutriates it. He makes it into a plastic paste with gum arabic and a little white soap, which he forms by moulding, as above, through a syringe, and drying, into crayons. The proportions of the ingredients require to be carefully studied.