Is That Real?: Identification and Assessment of the Counterfeiting Threat for U.S. Banknotes (2006)

This appendix describes the materials and manufacturing processes used in the production of U.S. banknotes. It discusses how these production elements combine to result in effective banknote features. The section on the vulnerability of current features describes some methods being used to simulate genuine banknote features.

Special papermaking and printing processes are required in the manufacture of U.S. banknotes in order to implement their design. The features of a U.S. banknote fall into three general categories: (1) substrate, (2) additional elements, and (3) the printed image. These features can be detected through visual means, through tactile means, and through a variety of detection schemes that are augmented by devices. It is important to understand how these features are produced in order to understand their interactions with one another and their effectiveness in U.S. banknotes.

The cotton and linen paper that is the substrate for U.S. banknotes is not only a base for the printed image and additional substrate elements, it is also a feature itself. The substrate is an intentionally designed feature of currency—it contributes to the look of the note, the feel of the note, the denomination of the note, and the authenticity of the note. The distinct feel of a crisp, new bill is very recognizable. Through engineering of the paper substrate, this characteristic feel can withstand folding, crumpling, soiling, and even laundering.

The substrate also has a distinctive look. The paper used for U.S. banknotes is a blend of two cellulosic plant fibers, flax (also known as linen) and cotton. It is supplied to the Bureau of Engraving and Printing (BEP) by a single manufacturer, Crane and Company in Dalton, Massachusetts. Processing of the substrate, which is tightly controlled, includes the use of selected plant fibers and additives and the development and use of specialized methods for pulping, washing, refining, screening, pressing, and bleaching.

The sources of raw materials are selected by optimizing quality and cost. Both the flax and cotton materials are primarily sourced from waste products from the textile industry. This approach is cost-effective because papermaking can utilize the shorter fibers that make poor thread for cloth. Currently, U.S. currency is made from nominally 25 percent flax and 75 percent cotton fibers. An assortment of papermaking chemicals—color, strength, and sizing agents—are added to the raw materials. No starch or

BOX B-1 Papermaking FIGURE B-1 The structure of cellulose (ß-1,4-D-glucopyranose). Cellulose, the most abundant natural polymer on Earth, is the major component of all papermaking fibers, including those used in the manufacture of U.S. currency. This natural polymer is composed of long linear chains of ß-1,4-glucopyranose in the 4C1 chain conformation with equatorially oriented hydroxyl groups as illustrated in Figure B-1. The degree of polymerization of these chains ranges from 15,000 for unprocessed cotton to as low as 1,000 in a bleached kraft pulp. The hydroxyl groups on these linear cellulose chains form strong hydrogen bonding networks within and between cellulose chains. Although cellulose has four crystalline polymorphs (cellulose I, II, III, and IV) only cellulose I is found in nature. Bundles of cellulose molecules, known as microfibrils, have been shown to contain both crystalline (50 to 70 percent) and amorphous regions. Cellulose-to-cellulose hydrogen bonds are the primary theoretical fiber-to-fiber bonding mechanism. The maximizing of the fiber surface area, fiber-to-fiber contact, and hydrogen bonding are important factors in the optimization of fiber-fiber bonding. Fiber surfaces available for bonding may be developed during the beating/refining of cellulosic pulps owing to internal and external fibrillation. In general, the greater the fiber surface area available, the greater the extent of bonding. Fiber-to-fiber contact occurs when water is removed during wet pressing and the drying process. In cellulose, hydrogen bonding occurs between hydroxyl groups. Many different high-volume grades of virgin paper exist. In essence, the papermaking process is an aqueous-based system in which cellulosic plant fibers are first mechanically treated to remove impurities and improve subsequent process stages. The next stage is often a pulping treatment that chemically removes unwanted materials. The resulting pulp is screened, washed, and may undergo subsequent chemical bleaching. The processed cellulosic fibers may then be mechanically refined to enhance the fiber bonding capacity before introduction into the papermachine. At the papermachine, the pulp is diluted and delivered to a porous moving belt or drum that facilitates water removal and the initial formation of a sheet of paper. In subsequent operations, presses and drying cylinders are used to remove the remaining water. In addition, papermakers utilize the papermachine to introduce an assortment of papermaking chemicals that enhance physical and optical properties of the paper. In the production of currency paper, manufacturers extend the capabilities of the papermaking process to facilitate the controlled introduction of watermarks, colored threads, security strips, and other anticounterfeiting technologies.

clay agents are employed in currency paper, although these are added to most other high-quality papers to improve brightness. This difference contributes to the unique look of currency paper.¹ See Box B-1 for further details on papermaking, which convey the difficulties inherent in duplicating the “feel” of genuine currency paper.

A number of additional items are added to the substrate during the papermaking process. These include short fibers that are visually apparent as short red and blue threads in the paper itself. A

watermark is made during the papermaking process in the $5, $10, $20, $50, and $100 notes. The watermark depicts the same historical figure as that shown on the respective bills’ engraved portraits.

Higher-denomination notes also incorporate security strips, made of thin plastic embedded in the notes in the final stages of papermaking; these are marked by metallic print indicating the denomination of each note. In newer notes, the strip also contains a tiny graphic of American flags.² The strips have a unique position on each denomination as well as a unique fluorescent color under ultraviolet lighting: The $5 strip is blue; the $10, orange; the $20, green; the $50, yellow; and the $100, red.³

Specifications for the paper, including the embedded elements, ensure that U.S. banknotes have a consistent look, feel, and strength. These specifications encompass thickness, opacity, roughness, porosity, resistance to tearing, tensile strength, fluorescence, folding endurance, thread bonding, color, ash, pH, and embedded-fiber density.

After the paper is delivered to the BEP as stacks of cut sheets, it is printed in a multistage printing process, front and back. Each sheet will be cut into 32 U.S. banknotes at the end of the printing process. For the $10, $20, and $50 notes, the first step is an offset process that prints a colored background simultaneously on the front and back of the sheet of notes. The background offset-printed colors are different for each denomination. The offset press is capable of maintaining register within approximately ±0.008 millimeters.

Next, the sheets are intaglio printed in separate steps on the front and back. The largest and most noticeable element of the intaglio-printed image is the portrait ($5, Lincoln; $10, Hamilton; $20, Jackson; $50, Grant; $100, Franklin). The portrait is also printed slightly off-center to open up space to enable the addition of the watermark and also to reduce image wear caused by folding the note in half.

On all but the $1 and $2 notes, the portrait is large enough to accommodate microprinting and fine-line details. Microprinting is used to print 0.2 mm tall letters with a line width of 0.05 mm. The production line width is approximately 0.1 mm, with a spacing of 0.1 mm. Microprinting and fine-line printing are used because they are difficult to reproduce with low-resolution electronic devices and can be viewed by the sharp-sighted or with a simple, low-power magnifier.

Inks are used in a variety of ways in banknote printing to create security features in the images. For example, infrared and magnetic patterns are incorporated that can be detected by machine.⁴ Color-shifting ink is used to print the denomination in the lower right corner of the $10 notes and higher denominations. The ink is optically variable, and shifts colors on the older $10 and $100 notes from green to black, and from copper to green on the new $10, $20, and $50 notes.⁵ The printed image on the note also contains “symbols of freedom” such as a torch ($10), an eagle ($20), and a national flag ($50). All of the inks used are purchased from a single source, SICPA, headquartered in Lausanne, Switzerland. SICPA provides security inks for over 85 percent of the world’s banknotes.⁶

Finally, the offset printing on the newest notes (the redesigned $10, $20, and $50) contains two additional features aimed at counterfeit deterrence. Patterns and ink colors known as the banknote detection system (BDS) are used to prevent counterfeiting using color copiers. An additional digital counterfeit deterrence system (CDS) is also incorporated into the line pattern that interferes with the ability to reproduce banknotes digitally.

While it is very difficult to say with certainty which are the most important features on current notes, there are some indicators for which features are important to the different types of users of banknotes:

• The features most used by the general public are reported to be the overall “look” and the overall “feel” of the note. The discriminators reported in checking for counterfeits when a banknote looks or feels different include the watermark, security strip, color-shifting ink, fine lines, and microprinting.

• The features most used by current machine readers are the transmissive optical spectrum and printed image, magnetic patterns, ultraviolet fluorescence, ultraviolet spectrum, and the infrared properties. Low-end readers may sense only one feature; high-end readers may use 10 or more measurements to authenticate and denominate each note.

• The features most used by the blind community to authenticate notes are the tactile features. There are no features available for use by the blind public to denominate or authenticate U.S. banknotes without using a machine reader.

It is interesting to note the overlap in responses of these users; both general and blind users identified the importance of the tactile feel of the note. It is also interesting to note which features are not used. For example, most overt counterfeit-deterrent features—such as the color-shifting inks, substrate properties, watermark, security strips, microprinting, and the Federal Reserve seal—are not currently used by machine readers because they are difficult to sense, to locate, or to verify. These features are also apparently rarely used by the general public, and some are not used at all, even by experienced cash handlers.

A variety of vulnerabilities drive currency design. Overall, features can be vulnerable in two main modes, and the two have less to do with trends in digital equipment and more to do with criminal motivation. Table B-1 summarizes the various printing processes considered, their quality implications, spatial resolutions, and general costs. This table provides a quick review of the processes available to the counterfeiter and their relative vulnerability as well.

As has been discussed, every feature on a U.S. banknote today is vulnerable to determined counterfeiters. These counterfeiter are willing to seek out specialized materials and equipment and are willing to search the Internet for special inks, image files, and tips on which digital printers and software will make a good counterfeit. Their motivation is criminal gain, which drives the depth of their effort and the scale of their operation.

Deterring a determined counterfeiter is possible through the combination of (1) features that are difficult to simulate and (2) an educated cash-handling public that is inspired to understand the distinctive nature of these features. However, there are no features on currency today—issued by any country—that a dedicated counterfeiter would find impossible to simulate and pass into circulation.

Casual counterfeiters, conversely, are more easily deterred. These counterfeiters may use equipment and materials that are easily accessed to make a few “pretty good” notes on an occasional basis. They are motivated merely by the opportunity; for example, they may take unwitting advantage of the lack of banknote detection systems in all-in-one devices or cell phone cameras. Today’s U.S. banknote provides

only a few features that would deter such a counterfeiter. However, even if a counterfeiter makes no attempt to simulate the more difficult features, an uneducated public can facilitate their quick financial gain.

A larger threat is looming as well: the increasing availability of currency-accepting devices that remove the human cash handler from the transaction. The growth in the use of these devices is expected to eventually balance the importance of human-recognized and machine-readable features in deterring currency counterfeiting. A result of the wider availability of cash accepters is the possibility that they can more easily fall into the hands of potential counterfeiters. The would-be crooks, including hobbyists, could easily refine their methods until their notes are accepted by the reader. One possible way to address this activity is to incorporate technology in currency readers that flag such efforts.

Users of U.S. currency have a habitual knowledge of the color and feel of the substrate. The color of the paper is not printed but is a result of the complex papermaking process, and the feel is unique to the fibers inside and the printing on the note.

In order to incorporate genuine currency paper into their products, some counterfeiters use common household bleach on $1 notes. By masking most of the printing on the note, for example, only the denomination might be bleached away and then reprinted. This technique has been made much easier through the ability of printers to handle thicker paper and new color-matching capabilities.

The color of the traditional intaglio-printed ink and of the new offset-printed background inks is also imprinted in the subconscious of many users of U.S. banknotes. Today, the subtle colors in many currencies are created using spot color inks and pigments. Many of these are nearly impossible to reproduce with a conventional desktop printer’s combination of cyan, magenta, yellow, and black (CMYK) inks. However, new software and hardware tools are emerging that can improve an RGB (red, green, blue) monitor’s WYSIWYG (what you see is what you get) color capabilities. These tools are intended to enable an artist working in CMYK to more accurately repair color problems on-screen before having to surmount the hardware issues within an RGB printer’s software. These tools are common among experts today.

A simpler approach to circumventing the limitations in standard color reproduction may be to empty an ink-jet cartridge and refill it with spot color ink. This could more perfectly reproduce the characteristic green that says “money” to most people. Duotone printing provides another low-cost tool to the counterfeiter.

Magnetic ink is a particularly difficult material to simulate. One solution is to incorporate nanoscale magnetic particles into suspension in today’s inks. The chemistry of ink-jet inks is very complex, but it may be very reasonable to suspend magnetic nanoparticles in them for the short times—on the order of hours—needed to print hundreds or thousands of sheets.

Finally, novel methods of using image-acquisition and image-processing software can more easily simulate the features on banknotes. For example, instead of scanning an entire note and re-creating it line by line, the tools common to today’s art software can enable a would-be counterfeiter to scan and edit features independently. This approach looks at selected portions of the note one at a time and is done in sizes and ways that are allowable under current usage constraints.⁸ Because a counterfeiter may only scan and incorporate the features that make a note easy to recognize, many printers and copiers may not recognize the final product as a banknote. In addition, once a counterfeiter completes this task, it is a simple matter to share the image file with others via the Internet.