In the SGAA Reference & Technical Manual: A Comprehensive Guide to Stained Glass, 2nd ed. Lee's Summit, MO: The Stained Glass Association of America, 1992, p. 82, Richard Millard describes graphic delineation:
“Lead lines fall into two basic classifications – graphic delineation and structural necessity, each of which serves a different purpose. “
“Graphic delineation, as the name implies, is a leading that delineates the design element or elements. It outlines and contains the major distinctions in the composition, and provides independent of color, a design statement unto itself. Its primary purpose is aesthetic, though it likely will also contribute structurally. Being of primary design import, it is governed by the aesthetic in its configuration. Its design responds to the shapes and sizes of that which it encompasses and frequently may consist of leads of varying thickness for contrast, accommodation, and fulfillment of the aesthetic. Such leading variations respond to the needs of visual emphasis by the use of wider or narrower lead. It provides the ‘line’ of the design and the containers that separate the colors of textural variations.”
“Those leads of structural necessity should have, as their major purpose, support of the graphic delineation in such a manner as to 1) provide the required structure, and 2) do so in a manner which visually accommodates and does not intrude upon its aesthetic.”
Does this fit your description of arbitrary lines? If not, I'll try again! I would be happy to send a copy of the pages from the SGAA manual that describe "line, design and structural concepts" if you'd like.
Please let me know if I can provide further information.
