What Contour Lines RepresentWhen contour drawing, we are focusing on the edges - the outside of an object or the line made by a fold or pattern. Don't get fooled into using the line to draw light and dark. The WEIGHT of a line, that is, how dark and thick it is, will make it jump out from the paper (if it is a strong, dark line) or sink into the paper (if it is light or thin). This is useful when you are trying to give the impression of something being closer or further away. For an illustrated guide to using contour lines, read this illustrated article on Pure Contour Drawing
Describing FormThe line that goes across an object, hinting at the form, is called a cross-contour. These lines don't usually describe an actual edge, and are often broken or 'implied', with a definite line at the start and end but with the pen lifted and re-applied to create a gradual gap in the middle. This suggests the more subtle changes in the surface of the object. To learn more about using cross-contours, read this article on Cross Contour Drawing.
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