Engraving the master die
- 1 Engravers hand cut the design into a piece of soft steel, known as the master die, using very fine engraving tools and a magnifying glass. The portrait and images consist of numerous lines, dots, and dashes which are cut in various sizes and shapes. The fine crosshatched lines in the background of the portrait are produced by a ruling machine, and the scrollwork in the borders are cut using a geometric lathe.
- 2 First the signatures are photographically enlarged. An engraver then traces the signatures by hand with one end of a device known as a pantograph. This motion is mechanically reduced through a set of linkages, causing several diamond-tipped needles on the other end of the pantograph to cut the signatures into the master dies.
Making the master printing plate
- 3 Once the master die has been inspected, it is heated and a thin plastic sheet is pressed into it to form a raised impression of the design. Thirty-two of these raised plastic impressions are bonded together in a configuration of four across and eight down to form what is known as an alto. The master die is then placed in storage.
- 4 The plastic alto is placed in an electrolytic plating tank and is plated with copper. The plastic is stripped away leaving a thin plate of metal, known as a basso, with 32 recessed impressions of the design. The metal basso is then cleaned, polished, and inspected. If it passes inspection, it is plated with chromium to make the surface hard, and it becomes a master printing plate.
Printing the front and back of the bills
- 5 The principal printing process is known as intaglio printing. This process is used because of its ability to produce extremely fine detail that remains legible under repeated handling and is difficult to counterfeit. A stack of 10,000 sheets of paper is loaded into a high-speed, rotary intaglio printing press. Each sheet is sized to allow 32 individual bills to be printed on the same sheet. The paper is inspected to ensure that it contains the proper security thread for the denomination to be printed. A master printing plate of the proper denomination is secured around the master plate cylinder in the press.
- 6 The rotating master printing plate is coated with ink. A wiper removes the ink from the surface of the plate, leaving only the ink that is trapped in the engraved recesses of the design. A sheet of paper is fed into the press where it passes between the master plate cylinder and a hard, smooth impression cylinder under pressures reaching 15,000 psi (1,034 bar). The impression cylinder forces the paper into the fine, engraved lines of the printing plate to pick up the ink, leaving a raised image about 0.0008 in (0.02 mm) above the paper. This process is repeated at a rate of about 10,000 sheets per hour.
- 7 The printed sheets are then stacked on top of each other. The backs are printed with green ink first and are allowed to dry for 24-48 hours before the fronts are printed with black ink.
Printing the colored Treasury seal and serial numbers
- 8 After the intaglio printing process, the stacks are cut into two stacks of 10,000 sheets and are visually examined for defects. Each sheet is fed into a letterpress which prints the colored Treasury seal and serial numbers on the face of the bills. Sixteen serial numbers are printed at the same time. The press then automatically advances the numbers before the next sheet of sixteen is printed. The numbers on any sheet are separated by 20,000 between adjacent bills. Thus, the bill in the upper left-hand corner of the first sheet would be serial number 0000001 and the one below it on the same sheet would be 0020001, and so on. On the second sheet, all the numbers would advance by one giving 0000002 in the upper left, 0020002 below it, etc. In this manner, when the sheets are cut into separate stacks, the bills within each stack will have sequential serial numbers.
- 9 The finished sheets are inspected with machine sensors, and any printing errors, folded paper, inclusion of foreign objects, or other defects are identified. Any bills which are found to be defective are marked for later removal. Such bills are replaced with star notes which are numbered in a different sequence and have a star printed after the serial number.
Cutting and wrapping the bills
- 10 The sheets are gathered in stacks of 100 and cut into 16 individual stacks of 100 bills each with a vertical guillotine knife. Any bills which have been identified as defective are replaced with star notes at this time. The stacks of 100 bills are then wrapped with a paper band. The banded stacks are given a final visual inspection and are shrink-wrapped with plastic in bundles of 10 stacks. Four of these 10-stack bundles are then wrapped together to form a "brick" before they are shipped.