A single-color photographic proof exposed from negatives prior to platemaking used to evaluate pagination and location of page elements, such as text, photos, and other illustrations. Since bluelines (which can also be brown—in which case they are called brownlines) are produced in only one color, the color breaks are not directly exhibited, but variations in exposure can indicate somewhat crudely where divisions in color will occur.
Bluelines are also called blues, and have variously been known as brown print, Dylux, silverprint, VanDyke, and Velox, names derived from the brands of photosensitive paper used to create them.