Joel Zlotnick, Jordan Brough and Troy Eberhardt

Initial papers in this series described reverse engineering of genuine document artwork[1] and introduced security design strategies to combat reverse engineering, including the use of a mono­chromatic colour gamut[2] and varying the opacities of inks within that gamut[3]. More recent papers considered split fountain printing as a technique for prevention of artwork replication[4] and for presentation of false split fountain opacity transitions[5]. This Part 6 paper begins an exploration of split fountain hardware, focusing on how the variable of split fountain placement can support the creation of artwork resistant to reverse engineering.

The broad goal of the monochromatic design paradigm presented in this series is to prevent individual plate images from being extracted from a security document, which forces counterfeiters to simulate, rather than replicate, individual plate artwork. Previous papers described the layering of monochromatic inks of different opacities and the use of split fountain printing for transitioning opacity instead of colour. This paper expands on the concepts of split fountain concealment and false split fountains developed in Parts 4 and 5 of this series. Unlike Parts 4 and 5, this Part 6 paper explores the first of three split fountain hardware variables: the positioning of split fountain hardware across the width of each ink station.

As in previous instalments of this series, this work is theoretical. Implementation of these concepts in real security artwork and printing environments would require press testing. Quality control, inspection, plate registration and other factors important in printing workflows are not addressed. For simplicity the opacities of overlapping layers of inks will be treated as if they are linearly additive regardless of print order or ink layer thickness; this cannot be assumed in real prints.

Split fountain hardware variables
Several hardware variables can be customised in split fountain printing, such as:

  • the locations where different pure inks are applied to ink rollers;
  • the amount of movement of the oscillator rollers that control the width of the transitions between the pure inks;
  • the number of pure inks deployed in each fountain.

Previous split fountain discussions in Parts 4 and 5 of this series only considered four ink stations with identical split fountain hardware configurations, and did not change hardware variables between ink stations. This paper examines changing the horizontal placement of split fountains, each involving only two pure inks, in each of four ink stations with identical roller oscillation. Roller oscillation and the number of split fountains in each station will be examined in later papers.

The examples below illustrate how changing the placement of split fountain hardware in a four-station offset printing press, featuring two inks per fountain, can conceal the press setup by simulating false split fountains that appear to be composed of more than two pure inks. The first example (figures 1 through 10) uses sets of paired opposing split fountains, which allows simulation of three flat tones in the interest of design flexibility. The second example (figures 11 through 17) does not use paired split fountains, so it offers additional false split fountains and greater print complexity at the cost of the flat tones. The ink opacities and the general placement of those inks will be the same as described in Parts 4 and 5 of this series; the only variable changed is the split fountain position.

Figure 1: Opacities of pure inks delivered from each of four fountains on press, expressed as various combinations of inks of 8%, 18%, 30% and 44% opacity. The first two fountains are opposites of each other in terms of ink placement and split fountain position, as are the third and fourth fountains.

Figure 1 shows the distribution of inks across the four ink stations in a hypothetical offset printing press, using only inks of the same colour but of different opacities. Split fountains are used to transition between ink opacities, not between different ink colours. The first station features a split fountain transition between pure inks of 44% opacity at the edges and 18% left of the centre of the roller, and so on for the other stations and ink placements. The same two inks (44% and 18% opacity) are used in opposite positions in the first two fountains and the same two inks (30% and 8% opacity) are used in the third and fourth fountains, again with opposite placements. As mentioned before, these percentages are contrived for purposes of illustration and would be replaced with optimal real ink formula­tions in an actual print workflow.

Simulating flat tones
Part 5 of this series described the simulation of three discrete flat tones by overprinting identical solid artwork from two paired split fountain printing plates. The example will be revisited here to affirm that three flat tones can still be simulated even if not all of the split fountains share the same position.

Figure 2: Overlap of split fountain inks from figure 1 to simulate flat tones of constant opacity. These flat tones depend on certain fountains in figure 1 being configured as opposites of one another.

Unlike the example in Part 5 in which all split fountains were centred across the width of the roller, figure 1 shows that the first two fountains have opposite ink placements and show the position of the middle ink shifted left, while the third and fourth fountains are also opposites and similarly show the middle ink shifted right. figure 2 shows that three discrete flat tones can be simulated by overprinting only the first two fountains, only the third and fourth fountains, or all four fountains. If two split fountains are configured with opposing ink opacities and identical split fountain positioning, in concept a flat tone can be simulated regardless of where the split fountain transition occurs across the width of the rollers. The simulated flat tones in figure 2 mimic the presence of only one ink in a fountain, but figure 1 shows that every fountain on press actually contains two pure inks.

Simulating three inks in one fountain
Next, consider the overlap of the first and fourth fountains of figure 1 (or the second and third fountains). In figure 3, a fountain with more opaque ink at the edges is paired with another fountain that has more translucent ink at the edges, or the reverse. Unlike the combinations that simulate the flat tones in figure 2, the combinations in figure 3 combine fountains where the ink opacities are not exact opposites of one another, and where the split positions are different.

Figure 3: Overprinting of the first and fourth fountains, and the second and third fountains, from figure 1. These combinations simulate splits involving three inks, instead of only two.

The overlap of the first and fourth fountains produces an area left of centre that shows a combined opacity that is lower than at the edges of the rollers, and another area right of centre that shows a combined opacity that is higher than at the edges of the rollers. The visual effect is reminiscent of (but not exactly like) a single fountain that contains three pure inks of different opacities. The overlap of the second and third plates (also shown in figure 3) creates a similar effect, though the higher opacity region is to the left of the roller centre and the lower opacity region to the right. Figure 3 illustrates how two overlapping split fountain plates with different split fountain positions can simulate the presence of three pure inks, blended with split fountains and printed from a single ink station.

Simulating four inks in one fountain
From figure 1, consider the overlap of fountains one and three, or fountains two and four, to produce the combinations shown in figure 4. Both fountains in these pairs feature a higher opacity ink at the edges and a more translucent ink in the middle (fountains one and three) or the reverse placement (fountains two and four).

Figure 4: Overprinting of the first and third fountains, and the second and fourth fountains, from figure 1. These combinations simulate splits involving four inks, not just two.

When overprinted as shown in figure 4, combining the first and third fountains simulates a visual effect similar to four pure inks of different opacities printed from a single split fountain. The general appearance is of a more opaque orange with two less opaque bands, but on close inspection the left band is slightly lighter than the right because the opacities combined on the left and right sides are subtly different. The degree to which this difference is apparent is a design choice, and is a function of the specific ink opacities selected by the designer. A similar effect is produced by overlap of the second and fourth fountains, with the left band being somewhat more opaque than the right. Accordingly, the combinations in figure 4 appear to simulate the presence of four pure inks, blended with split fountains and printed from a single ink station.

Combining three split fountains
While figures 3 and 4 illustrate various combinations of two fountains, figure 5 shows combinations of three fountains. Essentially, each combination shown in figure 5 is composed of one of the flat tones shown in figure 2, plus one additional fountain from figure 1. The result is that the false split fountain transitions shown in figure 5 appear to be between exactly two pure inks, not three or four. Overall, the transitions in figure 5 look much like those in figure 1, though darker and with reduced contrast. Although these combina­tions are important additions to the press gamut because they offer additional false split fountain effects, the three-fountain combinations in figure 5 do not simulate the use of additional pure inks like the two-fountain combinations shown in figures 3 and 4.

Figure 5: Combinations of three of the fountains shown in figure 1. Individually, each of these combinations just looks like a darker version of one of the split fountains shown in figure 1 and does not simulate the presence of more than two inks.

Incorporating the flat tones
Figures 2 through 5 illustrate the distribution of inks across four rollers and the combinations that can be created by layering them, but they do not show plate artwork. To disguise the press setup shown in figure 1, security artwork should not display any of the real ink distributions in figure 1 in isolation because doing so would allow a counterfeiter to view individual plate artwork and ink placements, and potentially exploit these for reverse engineering. Instead, a more secure design could be created entirely and only from the combinations shown in figures 2 through 5.

Figure 6
Figure 6: Split fountain artwork composed of inks of 44% opacity at the edges and 18% opacity in the middle. The split fountain places the 18% ink to the left of the centre of the roller. This split position is the same as in figure 7.
Figure 7
Figure 7: Split fountain artwork composed of inks of 18% opacity at the edges and 44% opacity in the middle. The split fountain places the 44% ink to the left of the centre of the roller. This split position is the same as in Figure 6.
Figure 8
Figure 8: Split fountain artwork composed of inks of 30% opacity at the edges and 8% opacity in the middle. The split fountain places the 8% ink to the right of the centre of the roller. This split position is the same as in Figure 9
Figure 9
Figure 9: Split fountain artwork composed of inks of 8% opacity at the edges and 30% opacity in the middle. The split fountain places the 30% ink to the right of the centre of the roller. This split position is the same as in figure 8.
Figure 10
Figure 10: Composite artwork produced by overprinting of figures 6 through 9. This image shows three simulated flat tones in the paper airplane and eight false split fountains, none of which exist in the real press setup. The waves at the bottom of the design simulate split fountain transitions involving three or four pure inks.

As an example, individual plate artwork designs are shown in figures 6 through 9, and are combined in figure 10. The composite artwork shown in figure 10 is created entirely from the combinations described in figures 2 through 5, and every visible split fountain transition is actually a false split fountain simulation created by overlap of two or more plates. Simulations of fountains containing three inks (from figure 3) or four inks (from figure 4) can be seen across the continuous horizontal wave patterns at the bottom of the artwork. Finally, the paper airplane design shows all three simulated flat tones described in figure 2, though the actual press configuration only contains the split fountains shown in figure 1.

Abandoning the flat tones
The example illustrated in figure 1 incorporates split fountains designed as opposing pairs, which allows for simulation of the flat tones shown in figure 2. However, there is no requirement that security artwork must include flat tones. Figure 11 shows a different configuration containing the same four pure inks as shown in figure 1, but with a unique split fountain placement in every ink station.

Figure 11: Opacities of pure inks delivered from each of four fountains on press, expressed as relative opacity percentages from 8% to 44%. Unlike Figure 1, these fountains are not paired opposites and cannot simulate flat tones. Compare to Figure 1.

Unlike figures 1 and 2, in figure 11 the middle ink is in a different location in every fountain, which disrupts the pairings required to simulate the presence of the flat tones shown in figure 3. Instead, the individual roller opacity distributions of figure 11 combine to produce the eleven false split fountains shown in figure 12 by overprinting two, three or four rollers. In figure 12 the flat tones have been lost, but have been replaced with three additional false split fountains for a total of eleven false split fountain combinations. Figure 12 also shows a complex system of lighter or darker bands that differ in placement between various roller combinations, to the extent that it becomes difficult to describe the patterns as simulating the presence of three, or four, or some other number of pure inks. To take advantage of this increased complexity to further disguise the press setup from counterfeiters, the placement and intensity of these bands should be paired with security artwork that is intended to comple­ment and benefit from, rather than compete with or be interrupted by these uneven opacity distributions.

Figure 12: Overlap of split fountain inks from Figure 11 to create complex combinations of light and dark opacity. No flat tones are present. The eleven complex false splits shown here replace the combinations shown in Figures 2 through 5.
Figure 13
Figure 13: Split fountain artwork composed of inks of 44% opacity at the edges and 18% opacity in the middle. The split fountain places the 18% ink far to the left of the centre of the roller. Unlike figures 6 and 7, the split fountain positions are different between figures 13 and 14.
Figure 14
Figure 14: Split fountain artwork composed of inks of 18% opacity at the edges and 44% opacity in the middle. The split fountain places the 44% ink far to the right of the centre of the roller. Unlike figures 6 and 7, the split fountain positions are different between figures 13 and 14.
Figure 15
Figure 15: Split fountain artwork composed of inks of 30% opacity at the edges and 8% opacity in the middle. The split fountain places the 8% ink slightly to the right of the centre of the roller. Unlike figures 8 and 9, the split fountain positions are different between figures 15 and 16.
Figure 16
Figure 16: Split fountain artwork composed of inks of 8% opacity at the edges and 30% opacity in the middle. The split fountain places the 30% ink slightly to the left of the centre of the roller. Unlike figures 8 and 9, the split fountain positions are different between figures 15 and 16.

Figures 13 through 16 illustrate demonstration artwork that could be printed from the rollers shown in figure 11. Figure 17 shows the full composite artwork composed only from the eleven combinations shown in figure 12. To see the additional artwork complexity possible when each ink station features a unique split position, compare figure 10 to figure 17, particularly in the area of the paper airplane.

Figure 17
Figure 17: Composite artwork produced by overprinting of figures 13 through 16. This image is composed entirely of the eleven complex false split fountains shown in figure 12. Compare to figure 10, especially the paper airplane and the waves at the bottom of the design.

To truly replicate the individual plate artwork shown in figures 13 through 16, a counterfeiter would have to first reverse engineer the ink distributions shown in figure 11, starting only with the composite artwork in figure 17. Because of the complexity of such a task, attempts to replicate the artwork detail would likely be abandoned and the counterfeiter would be motivated to settle for a lower-quality method of halftone artwork simulation that could be easily detected microscopically.

Conclusion
This paper explored the positioning of split fountains as the first of three split fountain hardware variables that can contribute to security designs resistant to reverse engineering. Within the monochromatic design paradigm, the examples demonstrated that changing the position of split fountains between ink stations can simulate several visual effects. These include flat tones, the presence of additional pure inks that are not a part of the press setup, and complex patterns of higher and lower opacity, each of which can be developed in conjunction with appropriate security artwork according to the priorities of the designer. However, split fountain positioning is just one of three hardware variables associated with split fountain printing that will be examined in this series. Future work will explore the effects of varying the roller oscillation between fountains, and the split fountain transition between more than two pure inks in each station on press.

Please note: The views expressed in this paper do not necessarily represent those of the US government.

MORE ABOUT THE AUTHORS

Joel Zlotnick is employed by the US Department of State, Bureau of Consular Affairs, Counterfeit Deterrence Laboratory as a physical scientist. He conducts research on how design strategies can help maximise the security value of printing technologies and security features, and develops training programmes on counterfeit detection.

Jordan Brough is employed by the Homeland Security Investigations Forensic Laboratory as a forensic document examiner, specialising in adversarial analysis and counterfeit deterrence. Jordan spends his time examining suspect documents and consulting with United States security document designers.

Troy Eberhardt is employed by the US Immigration & Customs Enforcement Homeland Security Investigations Forensic Laboratory. He supervises the Research and Development Section at the laboratory, which specialises in identifying and mitigating vulnerabilities within travel documents.

References

1 Zlotnick, J., Brough, J. and Eberhardt, T. (2016). Interrupting traditional counterfeiting workflow, Part 1: Colour and split fountains, Keesing Journal of Documents & Identity, Vol. 49, pp. 14-19.

2 Zlotnick, J., Brough, J. and Eberhardt, T. (2016). Interrupting traditional counterfeiting workflow, Part 2: Monochrome colour gamut. Keesing Journal of Documents & Identity, Vol. 51, pp. 22-27.

3 Zlotnick, J., Brough, J. and Eberhardt, T. (2017). Interrupting traditional counterfeiting workflow, Part 3: Security design and ink opacity. Keesing Journal of Documents & Identity, Vol. 53, pp. 22-28.

4 Zlotnick, J., Brough, J. and Eberhardt, T. (2017). Interrupting traditional counterfeiting workflow, Part 4: Split fountains redux. Keesing Journal of Documents & Identity, Vol. 54, pp. 31-35.

5 Zlotnick, J., Brough, J. and Eberhardt, T. (2018) Interrupting traditional counterfeiting workflow, Part 5: False split fountains. Keesing Journal of Documents & Identity, Vol. 55, pp. 26-31.