In the early days of letterpress printing dampening the sheet was a regular way of improving the impression. When the paper is dampened however, it will expand. With one-color printing the difference in expansion of one sheet as against another wasn’t a problem anyone would notice. But multicolor printing was always complicated by this propensity of paper to absorb moisture and swell unpredictably. Keeping all your images in a multicolor job in perfect register was a nightmare. How could you ensure that the moisture in the sheet today was exactly the same as yesterday? This remains a problem, though we have addressed it now by making climate-controlled pressrooms. This minimizes the difficulty but doesn’t completely get rid of it.

Chromolithography was a 19th century phenomenon. Alois Sennefelder, inventor of lithography, did allude to the printing of color by lithography in his 1818 Vollstaendiges Lehrbuch der Steindruckerey. In 1837 Godefroy Engelmann of Mulhouse, France was awarded a patent. Chromo-lithography was always an expensive process: as many as 20 or 25 different impressions (therefore stones) might be involved in a single print, and the process was never much used in book-work. The level of skill involved is almost unbelievable to us now. In hand-printed chromo-lithography the image is applied to a stone plate with a grease-based crayon or ink. The stone is coated with a gum arabic solution and weak nitric acid, and then inked with oil-based inks which flee the gum and adhere to the grease crayon areas. Pressure is applied across the sheet by a doctor blade made of leather or wood, and this transfers the inks to the paper. Repeat with the next color, preserving perfect alignment, register, until all colors have been added.

IMG_0387This enlargement of a reproduction of a side-panel of the 1432 Ghent altarpiece by Hubert and Jan van Eyck shows the process of chromolithography. (You should be able to zoom in to see greater detail.) We are used today to seeing a regular screen in our halftones, breaking colors down into dots which looked at together mimic the colors in the original. In this example the screen isn’t a real screen: it’s a collection of hand-drawn stippling, more intensive in areas of high detail, less so in simpler areas. The printer would draw up a number of  black and white outlines of the picture (the number corresponding to the number of colors of ink to be used in the chromolithograph — Richard Benson reports that he has failed to work out exactly how many colors were used in this reproduction, but he has identified at least eight though there were “perhaps many more”: The Printed Picture p. 64). The separation of colors would be at the judgement of the printer, not based on any standard method such as we have nowadays. The printers would decide what ink colors, and how many different ones they’d need to reproduce the picture, and then by eye, break each color out onto a separate sheet of paper, shade in solid areas, and add stippling to allow for color blends. The amount of stippling for instance in the face is greater than in the sleeve. The drawing and stippling had to be done at final size — they had no means of enlarging/reducing — and this means this detailed work is phenomenally skillful. The resultant drawing then had to be transferred onto the stone (in itself no simple task) using a greasy ink or crayon.