How wood engravers created ink-less shadow lines that did not exist on the sheet of paper.

The techniques of creating a grey-scale range from black to white in wood engraving assumed the optical admixtures of white and black lines as was the tradition in metal engraving where the density of cross hatching for example controlled the amount of black ink and therefore shade or shadow on white paper. However as the size or scale of wood engraving increased in the middle of the nineteenth century wood engravers discovered another way to create the most subtle form of grey shadow by creating “lines” that held no ink but instead were an optical illusion that could be controlled or modulated with adroit cutting.

The wood engraving below is a portrait of the famous English caricaturist, George Cruikshank (1792 -1878) Printed in the Harpers Weekly 1875. May 22 p.417. (In the original, the engraved image is quite large at about 25 cm or 10 inches high. The focus here is on the lines contained in the outlined red rectangle as these distinct grey lines, and indeed the similar flowing lines on the right side of the background, as an optical illusion created by the cutting techniques of the wood engraver

The optical illusion being used by nineteenth-century wood engravers is known as the Hermann grid. The illusion is named after Ludimar Hermann (1838-1914), who wrote about it in 1870 although it is also sometimes called the Hermann-Hering illusion as Edwald Hering also presented extended analysis in 1872. For more information on the Hermann grid and other optical illusions see The Centre for the Study of Perceptual Experience (CSPE) University of  Glasgow.

The Hermann-Hering grid is probably best know in the art world for the discussion prompted by composite polaroid  works made by David Hockney in 1982. The polaroid photographs had a predetermined white border as part of their structure which meant that when mounted into a grid the Herman illusion or phenomenon was an inescapable outcome. Hockney only  briefly tolerated the pulsing blurs at the junction points of the white grid for one body of work and quickly moved on to his “joiner photographs” ( from 1982 to 1986 ) in which he collaged overlapping or abutted conventional colour photographs. 

Wood engravers obviously understood this illusion before the publication of it in 1870 since a sophisticated application of the illusion was being used by wood engravers to create illusory or invisible lines in their images. The example here is from 1875. The seemingly freely drawn looping lines in the background area of the George Cruikshank portrait above {as outlined in the red rectangle] appear to be a lighter grey but also much wider than the narrow linear parallel lines they cross.

By selectively fattening and narrowing the white line or manipulating the contrast between the black lines the Herring “shadow” or blur is created. As these 2400 dpi scans and the magnified video reveal, the grey shadow is a result an illusory effect. The cutting marks suggest, (remember the white is being cut away) the technique was created by first of all drawing the crossing lines on the block and it appears here even cutting them into the design before selectively relieving or cutting narrow channels through the line and widening the white line on one side or the other before cutting the narrow “channel” line. Other techniques were deployed to give different character to the shadow line such as cutting a very narrow white line parallel with it.

This video of the entire area around the red square or rectangle in the above engraving. It is filmed through a jewelers loupe and shows the extent of grey area created with the technique. Note how the grey line disappears only in the specific site where you focus your vision.