Page:Encyclopædia Britannica, Ninth Edition, v. 4.djvu/759

Rh colour to be applied is spread. The plate is then pulled backwards, the excess of colour being removed by a &quot; doctor/ and the colour rein lining on the engraving is then printed on the white cloth. Printing is now almost universally accomplished by means of cylinder machines, in which the impression is given by one or a series of engraved copper cylinders ; a different cylinder being required for each separate colour or shade in the pattern. Tho cylinders are made about 3 feet G inches long and 6 inches in diameter ; and in estab- Iishni3ats of any considerable extent many thousands of these are kept in stock, involving an enormous outlay of capital. There are three different methods in practice for engraving patterns or portions of patterns on the cylinders. In the first, the &quot; die and mill &quot; process, a cylindrical steel die is engraved with the pattern, which is afterwards trans ferred to a &quot; mill &quot; or cylinder of soft stesl. The pattern on the mill is in relief, and after hardening it is by pres sure impressed into the copper roller. The diameter of the mill is such that the repeats of the pattern fit with the utmost precision when transferred to the copper roller. The &quot; die and punch&quot; process is a modification of the fore going, in which small patterns are impressed on the copper cylinder by means of a punch which has the pattern in relief transferred to it from a sunk steel die. The third process by which engraved rollers are prepared is by the aid of the pentagraph, a most complex and ingenious michine, with which by the movement of a single tracer in the deep lines of an enlarged pattern cut in a zinc plate, these lines are reproduced on the original scale, traced at five different places through a coating of bitumin ous varnish on the surface of the cylinder. After the engraving is complete, the cylinder is placed in a bath of dilute nitric acid, by which the pattern is bitten in along the surfaces of the metal exposed by the scratching of the pentagraph points.

Calico-printing machines are arranged to print with any number of such cylinders, from one up to as many as twenty ; but in practice few machines carrying more than eight cylinders are employed. The accompanying dia grammatic section (fig. 1.) illustrates the arrangements necessary for printing one colour, and each of the separate colours on a ma chine is similarly mounted round the periphery of the central bowl or cylin der a. Against this central bowl a the engraved copper cylinder b presses, and between them the cloth to be printed and a thick cloth or blanket pass. The cylinder is supplied with the printing material by means of a furnishing rod- ler c, which revolves in the colour-box (I. The superfluous colour is removed from the cylinder by means of the colour doctor e, a steel blade which fits closely to the surface of the roller, and removes all colour except that which fills the engraved portions. The lint doctor/ similarly removes all impuri ties which adhere to the roller after it has communicated its impression to the cloth. Fig 2 shows the elevation of a six-colour machine by Messrs Mather and Platt of Manchester, to whose courtesy we are indebted for illustra tions of the most recent and approved forms of apparatus. The essential pirts of this machine consist of the central iron bowl or cylinder A, and the six radiating arms B, each of which holds in position an engraved roller colour- box, (fee., as shown in diagram fig. 1. By nuans of screws and other fine mechanical adjustments the pitch of each roller can be arranged so that its particular colour falls on the proper place with the utmost exactitude, producing a perfect pattern. In printing, the white calico is batched at C, and the cloth D passes inwards over tension rails, proceeding round the periphery of the bowl A, receiv ing from each roller B a separate colour or mordant, and issuing at D, printed and ready for the further processes to be hereafter detailed. Around the central b jwl A aro lapped, for the sake of elasticity, several folds of cloth. Between the central bowl and the cloth to be printed there passes, 1st, an endless band of cloth or blanket, seen enter ing at E and issuing at E ; and 2cl, a &quot; grey back&quot; or web of unbleached calico, used to keep the blanket clean, which enters at F and issues at F.

By whatever mechanical means the printing is performed, whether by hand-block, perrotine, or cylinder machine, the effect is precisely the same, and the colours or mordants employed are in all cases alike. The substances to be printed on the surface of the calico have to be brought to a proper consistency for printing by means of thickeners, with which they are mixed up in colour pans. Although these are only mechanical agents, it is found in the prac tical operation of printing that particular thickeners are more suitable for certain colours or mordants than others, and the printer is guided by experience in selecting that thickening adjunct which gives the clearest impression. Among the numerous thickeners available, those moot com monly employed are wheat flour and starch, potato starch, dextrin or British gum, and gum-senegal or other varieties of gum-arabic. The mordant or the colour and its appropriate thickeners are placed in a range of colour pans, in which the materials are thoroughly incorporated. A pair of these pans (one In section), as constructed by Messrs Mather and Platt, embracing the most recent and approved appliances, is shown in iig. 3. In the cut, A represents the driving pulleys, B the driving shaft, wheels, and catch-box, c wheels for giving a rotary motion to the brass stirrers d. E is the colour pan, of copper, double cased, made to swivel on centres or pivots/ 1 and /-. Through/ 1 water and through/ 2 steam are supplied to the space between the outer and inner body of the pan for the purpose of boiling and cooling down the contents of the pan alternately as required. The supply of steam or 