When the design, however, consists of straight parallel stripes of different colours, they may be applied by one block at a single impression. For this purpose the colours are contained in as many small tin troughs as there are colours to be printed. These troughs are arranged in a line, and a small portion of each colour is transferred from them to the woollen cloth by a kind of wire-brush. The colour is distributed evenly in stripes over the surface of the sieve by a wooden roller covered with woollen cloth. For the rainbow style, as a peculiar pattern is called, the colours are blended into one another at their edges by a brush or rubber. An important improvement has been made in the construction of hand-blocks, by the application of a stereotype plate as the printing surface. A small mould is produced from a model of the pattern, and the stereotype copies are then made by pouring mixed metal into it. A number of the stereotype plates are then formed into a printing block, by being arranged in a stout piece of wood. [Illustration: One of the Cylinders of the Machine, showing the way by which it is coloured.] The greatest mechanical improvement in the art of calico printing was the invention of the _cylinder_ or _roller_ printing at the end of the last century. This style of printing has been generally adopted in Lancashire, and is the cause of the success of the English over the continental printers. One cylinder machine, attended by one man to regulate the rollers, is capable of printing as many pieces as one hundred men and one hundred girls could print with hand blocks in the same time. A mile length of calico can be printed off with four different colours in a single hour. This cylinder machine consists of a hollow cylinder or roller of copper, about three feet long and three or four inches in diameter, the pattern on which has been produced by the pressure of a mill, on which the design has been originally stamped by the pressure of a hard steel roller which has been engraved. The copper cylinders are mounted on a strong iron shaft with a toothed wheel at its end, in order to put it in train with the rotatory printing machine for one, two, or more colours. On a roller at the upper part of this apparatus are wound the calico webs stitched together, the end of which is brought between the engraved copper cylinder and a large centre roller covered with blankets, against which it is made to bear with a regular pressure.