PAINTS, GRINDING OF

There are many pigments, such as common orpiment, or king’s yellow, and verdigris, which are strong poisons; others which are very deleterious, and occasion dreadful maladies, such as white lead, red lead, chrome yellow, and vermillion; none of which can be safely ground by hand with the slab and muller, but should always be triturated in a mill. The emanations of white lead cause, first, that dangerous disease the colic a pictonum , afterwards paralysis, or premature decrepitude and lingering death. IMG:4147767755307473660_illo0916a.png:Colour-mill IMG:4147767755307473660_illo0916b.png:Colour-mill Figs. 775 , 776 , 777 , 778. exhibit the construction of a good colour-mill in three views; fig. 775. being an elevation shown upon the side of the handle, or where the power is applied to the shaft; fig. 776. a second elevation, taken upon the side of the line c , d , of the plan or bird’s-eye view, fig. 777. The frame-work A A of the mill is made of wood or cast iron, strongly mortised or bolted together; and strengthened by the two cro iron bars B , B . Fig. 778. is a plan of the millstones. The lying or nether millstone C , fig. 776 , is of cast iron, and is channelled on its upper face like corn millstones. It is fixed upon the two iron bars B , B ; but may be preferably supported upon the 3 points of adjustable screws, pa ing up through bearing-bars. The millstone C is surrounded by a large iron hoop D , for preventing the pasty-consistenced colour from running over the edge. It can escape only by the sluice hole E , fig. 776. , formed in the hoop; and is then received in the tub X placed beneath. The upper or moving millstone F , is also made of cast iron. The dotted lines indicate its shape. In the centre it has an aperture with ledges G , G ; there is also a ledge upon its outer circumference, sufficiently high to confine the colour which may occasionally accumulate upon its surface. An upright iron shaft H pa es into the turning stone, and gives motion to it. A horizontal iron bevel wheel K , figs. 776 , 777. , furnished with 27 wooden teeth, is fixed upon the upper end of the upright shaft H . A similar bevel wheel L , having the same number of teeth, is placed vertically upon the horizontal iron axis M , M , and works into the wheel K . This horizontal axis M , M bears, at one of its ends, a handle or winch N , by which the workman may turn the millstone F ; and on the other end of the same axis, the fly-wheel O is made fast, which serves to regulate the movements of the machine. Upon one of the spokes of the fly-wheel there is fixed, in like manner, a handle P , which may serve upon occasion for turning the mill. This handle may be attached at any convenient distance from the centre, by means of the slot and screw-nut J . The colour to be ground is put into the hopper R , below which the bucket S is suspended, for supplying the colour uniformly through the orifice in the millstone G . A cord or chain T , by means of which the bucket S is suspended at a proper height for pouring out the requisite quantity of colour between the stones, pulls the bucket obliquely, and makes its beak rest against the square upright shaft H . By this means the bucket is continually agitated in such a way as to discharge more or le colour, according to its degree of inclination. The copper cistern X , receives the colour succe ively as it is ground; and, when full, it may be carried away by the two handles Z , Z ; it may be emptied by the stopcock Y , without removing the tub.