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How can thick and thin lines show changes in shape or lighting?

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Figure 1: Two techniques of representing an object. (A) Perspective drawing, suggesting that the object is cubical. (B) Orthographic top and front views, revealing that the object is not cubical. — drafting Figure 1: *Two techniques of representing an object.* (A) Perspective drawing, suggesting that the object is cubical. (B) Orthographic top and front views, revealing that the object is not cubical.

In the context of drawing, the variation of line thickness is a fundamental technique used to convey depth, form, and illumination.

Artists use the thickening or thinning of a line to indicate spatial changes or shifts in the color of an object. By adjusting the strength of a stroke, a draftsperson can effectively render light-and-shadow values, providing a sense of volume and corporeal appearance to a two-dimensional image.1

Beyond simple outlines, these variations help clarify the relationship between an object and its environment. For instance, slight shifts in the flow of a line can reinforce the effect of light striking a surface, helping to define smooth curves and transitions. While consistent, even-stroke textures are often used for ornamental purposes, the deliberate manipulation of line weight allows for a more pictorial and expressive representation of form.1