NCJ Number
186096
Journal
International Journal of Forensic Document Examiners Volume: 5 Dated: December/January 1999 Pages: 317-323
Date Published
1999
Length
7 pages
Annotation
This paper describes the three major printing processes--letterpress, lithography, and intaglio--along with their respective inks.
Abstract
The letterpress process is technically known as typographic, because it uses raised type and images to transfer ink to a substrate. This was the original printing process and used carved wooden blocks as the printing plate. The lithography process is technically known as a planographic process, because it uses a flat surface printing plate. The image areas are chemically differentiated from the nonimage areas. The most popular use of lithography is the offset process. The inked plate is pressed against a cylinder covered with a thin rubber blanket that transfers the image to the blanket. The blanket cylinder is then pressed with moderate pressure against the substrate, transferring the inked image to the paper. The intaglio process is commonly known as copper or steel engraved plate printing, because it uses recessed image areas. In document printing these may be hand or mechanically engraved directly into the surface of the metal plate. In operation, the recessed images are filled with ink and the surface of the plate is wiped clean. This is accomplished with special elastomeric inking rollers or fabric or paper rolls. The substrate, which may be predampened paper, is pressed against the plate under extremely high pressures. This forces the substrate down into the recesses in the plate, allowing it to contact the ink. On separation, a good portion of the ink in the recesses is transferred to the paper. In addition to describing these printing processes, this paper discusses the microscopic identification of prints; ink vehicle chemistry; ink colorants; ink additives; and analytical techniques used for printing inks. 2 tables, 10 figures, 2 references, and 5 suggested readings