This image was made using the four colour process, identified by the pattern of circles of dots visible through a magnifier and the squishing of ink visible at the edges of some of the tone, which distinguishes it as relief halftone rather than as halftone lithography (which would appear flat).
The three or four colour printing process was a colour version of halftone used with one colour (see previous caption), in which an image was photographed through a screen and exposed onto a light-sensitized metal plate, which was then relief-etched. The screen reproduced the image as a series of dots varying in size depending on the intensity of colour required. For full colour images, however, an additional stage was needed as separate plates were needed for each of three colours – cyan, yellow and magenta – and the additional black plate, if used. The original design or image was therefore photographed through coloured filters to separate the colours out. The screen was positioned at a slightly different angle when each colour was photographed so that the resultant patterns of dots would lie in different positions and, when printed, combined to form multi-colour circles giving the impression of full colour.
The dots can be seen through a magnifier and vary in shape depending on the colour being reproduced. A single primary colour of yellow will form a grid pattern composed simply of yellow dots of varying sizes, while a more complex colour will appear as a multi-coloured circle of dots.