Whilst researching methods for making marks to suggest tone and shading I came across the term Bracelet Hatching. I looked it up online, but struggled to find a good explanation of it. I finally came across an article (http://www.rogerconlon.com/5-contour-systems—bracelet-shading.html) which referred to the technique as bracelet shading- using contour hatching
“as if each [3D object] has a wire bent around it to reveal its three dimensional shape or form,”
using a drawing by Durer as an example. I have just bought a book about Durer from the National Gallery and realised he was referring to a method I had already observed and admired, for example in the drawing below:
In this drawing, Durer: Six Nude Figures (1515), http://www.wikiart.org/en/albrecht-durer/study-sheet-with-six-nude-figures-1515, depth and form are added to the shapes of the bottom of the tree and musculature by parallel contour lines. Increasing depth of shadow is intimated by increasing the frequency of lines and making each line darker.