With the introduction of the redesigned $20s in 2003, subtle background colors were added to the currency to enhance the security. For these denominations, offset printing is the first printing that occurs on the "blank" paper.
Before the subtle background colors of today's redesigned currency can be printed, the imagery must be transferred onto offset printing plates. That is the job of photoengravers. The photoengraver receives the master design from the bank note designer and "steps" (duplicates) the images over a plate layout. Then using a high-resolution laser image sensor, each color separation is imaged onto a sheet of sensitive film in negative form. A thin sheet of steel, coated with a light-sensitive polymer, is exposed to ultraviolet light while covered by the film negative which contains the imagery. The areas on the film that allow light to pass onto the plate are transferred or exposed. The unexposed areas around the images are washed away with water and soft scrubbing brushes. This process is called "burning a plate."
The background colors are then printed by the BEP's Simultan presses, which are state-of-the-art, high-speed, sheet-fed rotary offset presses. These presses are over 50 feet long and weigh over 70 tons. Using dry offset plates, ink from the plate is transferred to an offset blanket. The blank sheet of paper passes in-between the face and back blankets and simultaneously prints the complete image on the paper. The press has eight print units, four on the face and four on the back, with two comprehensive computer control consoles. Many of the press settings can be controlled from these consoles and their status displayed on the computer screens. The press is capable of printing 10,000 sheets per hour; approximately every 500 impressions, the press operators will pull a sheet and carefully examine it to ensure that all the colors are remaining consistent.
These sheets are stored for 72 hours to dry before going on to the next section, plate printing. Drying occurs in Work-In-Process security cages, otherwise known as WIP cages. On average, the BEP inventories 2,000,000 sheets (or 100 loads) between offset printing operations and the back plate printing operation.