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"A conical surface may be shaded by driving a fine needle at the apex and swinging a triangle about it, as in (A). To avoid a blot at the apex of a complete cone the needle may be driven on the extension of the side as in (B), or it may be shaded by parallel line as in (C)." —French, 1911

Different Cone Shading

"A conical surface may be shaded by driving a fine needle at the apex and swinging a triangle about…