This is the fourth in a series of five papers about optimizing simultaneous offset, a hardware security printing technology that applies offset images in register between the front and back of a substrate.  Part one of this series described icon artwork and registration, multiplate simultaneous offset images, and traditional and digital counterfeiting workflows. Part two covered inspection ergonomics, icon placement, integration of simultaneous offset with other offset security features, and four visual/perceptual effects: image completion, image disappearance, contrast increase and color change.  Part three explored novel applications for color change and saturation change effects in simultaneous offset.  Building on color concepts from part three, this part four paper focuses on contrast effects and some strategies for resisting digital counterfeiting, including integration of simultaneous offset with specialty inks and split fountains. 

About the Mockups

Throughout this paper mockups illustrate a range of potential simultaneous offset designs and visual effects.  These are simple graphics just for illustrating concepts but could be adapted for real security designs to include more complex artwork, additional plate images, more ink colors and multiple visual effects.  For simplicity, the mockups assume ideal ink behaviors and quality control considerations are not addressed, though these factors cannot be ignored in real printing environments.  Each manufacturer will reach its own conclusions regarding which strategies (if any) are appropriate for its own workflows or the needs of a particular document.      

Throughout the Figures, examine how the front and back artwork coordinate for specific contrast effects.  In a genuine document, what visual effect is produced when the plate images are registered correctly?  How is this visual effect derived from the plate art design and differences in how the inks behave in reflected vs. transmitted light?  How could the icon be described in training materials?  If images were out of register in a counterfeit, how would users become suspicious?  How does combining simultaneous offset with specialty inks and split fountains force difficult simulation and registration problems on digital counterfeiters?

Contrast and Saturation

From part three of this series, a color-changing simultaneous offset icon requires the intersection of front and back artwork in transmitted light and always results in a darker image.  However, the design approaches needed to create monochromatic contrast effects like image disappearance, image change and image movement are different.  Monochromatic simultaneous offset design strategies are compatible with general methods for monochromatic design1,2, from prior work. 

First, revisit some contrast examples from parts two and three of this series. Figure 1 shows a two-plate icon mockup in which the front and back images are identical.  In transmitted light saturation increases as both ink layers block light together.  Misregistration in a counterfeit would result in doubling of the icon artwork when viewed in transmitted light.  Figure 2 shows this technique in an issued banknote, where the icon interior incorporates four plate images instead of two. 

Figure 1. Mockup simultaneous offset design with one plate on the front and one on the back, showing identical artwork on both sides. In transmitted light both ink layers can be seen at the same time, resulting in higher contrast and saturation. This concept is shown in an issued banknote in Figure 2. 

Figure 2. Contrast-increasing simultaneous offset design in an issued banknote. The same symmetrical artwork is printed on the front and back, so viewing in transmitted light causes the contrast and saturation of the design to increase as the amount of ink in the design essentially doubles. Because the artwork outside the border of icon does not match between the front and back, it becomes blurry in transmitted light. Compare to the mockup shown in Figure 1.

The opposite of the strategy used in Figures 1 and 2 is the positive/negative artwork in Figure 3.  In reflected light each side shows a star, circle, and pattern of stripes, but in transmitted light, each image completes the other without overlap such that the artwork vanishes.  If out of register in a counterfeit, both the front and back images would remain visible in transmitted light.  For purposes of user training, this could be described as an image disappearance feature.  Figure 4 is an issued banknote that includes positive/negative images inside the icon, but artwork density is also balanced outside the icon to keep the color intensity even throughout the transmitted light image. 

Figure 3. Mockup simultaneous offset design with one plate on the front and one on the back, with the front and back artwork configured as negative images of one another. In transmitted light the view is of a flat tone. This visual effect could be described either as a reduction in contrast or as an “image disappearance” feature where the reflected light images vanish in transmitted light. This concept is shown in an issued banknote in Figure 4. 

Figure 4. Contrast-reducing simultaneous offset design in an issued banknote. The front and back of the icon art are negative images of one another, so viewing in transmitted light causes the images on one side to fill in the voids on the other and the text vanishes. The ink coverage is also balanced outside the icon such that the icon itself also disappears. This visual effect could be described as a contrast reduction or as an “image disappearance” feature. Compare to the mockup shown in Figure 3.

Combining aspects of Figure 1 and Figure 3, the mockup in Figure 5 shows increasing and decreasing contrast together in a single design.  In transmitted light, the saturation of the circle increases because the circle art is the same on both sides, but the stripe pattern disappears because the stripes on the back are a negative image of the stripes on the front.  

Figure 5. Mockup simultaneous offset design incorporating elements of both the contrast-increasing designs shown in Figures 1 and 2 and the contrast-reducing designs shown in Figures 3 and 4.  In transmitted light, the stripes disappear but the circle around the star becomes darker, illustrating how artwork choices can facilitate the inclusion of multiple contrast effects within a single simultaneous offset design. 

Image Change and Movement

The mockups in Figures 1, 3, and 5 include only one front plate and one back plate, but Figures 6A (individual plate images) and 6B (composite images) show how a second back plate facilitates an image change effect.  In transmitted light, the first back plate fills in the star (contrast reduction) and the second back plate add the circle (image appearance).  User training could describe a change from a reflected light star to a transmitted light circle.  In this example, the back artwork is fully subordinated to the front artwork, so this strategy might be better for documents in which back artwork is often omitted anyway (i.e. birth records) but not where the back artwork is usually a separate design (i.e. banknotes). 

Figure 6A. Mockup simultaneous offset design including one front and two back plate images, all composed of the same ink color. Viewed in transmitted light from the front, the first back plate image is designed to fill in the star-shaped void in the front plate image, reducing its contrast and causing the star shape to disappear. The second back plate introduces a circle shape to the transmitted light image.  Composite front, back and transmitted light images are shown in Figure 6B. 

Figure 6B. Composite images from the individual plates shown in Figure 6A. In reflected light, the front image contains a star design void. In transmitted light, the two back plate images simultaneously make the star disappear and introduce the circle in its place. This visual effect could be described as an “image change” feature, or also as a simultaneous increase and reduction in contrast in different areas.

The image change in Figures 6A and 6B was in the center of the icon, but a similar strategy also produces image movement.  In Figures 7A and 7B, the first back plate eliminates the front plate image and the second back plate adds a new image in a different location, creating a movement effect as the star relocates from the left (reflected light) to the right (transmitted light). 

Figure 7A. Mockup simultaneous offset design including one front and two back plate images, all composed of the same ink color. The first back plate image is designed exactly as a negative of the front and its purpose is to eliminate the reflected light front image from the transmitted light view. The second back plate reintroduces the star design, but in a different position.  Composite front, back and transmitted light images are shown in Figure 7B. Compare to Figure 8A.

Figure 7B. Composite images from the individual plates shown in Figure 7A.  In transmitted light, the two back plate images simultaneously remove the star and circle design from the lower left area and cause it to move to the upper right. This visual effect could be described as an “image movement” feature, or equally as a simultaneous increase and reduction of contrast in different parts of the design. Compare to Figure 8B. 

Figures 8A and 8B are the same artwork as Figures 7A and 7B, but with different ink opacities.  In Figure 7A, the front and first back plate contain the same ink but the second back plate contains an ink of higher opacity.  Compared to Figure 7B, contrast in the transmitted light image in Figure 8B is improved because the two positive/negative image plates in Figure 7A are lighter than the second back plate.

Figure 8A. Mockup simultaneous offset design of the same artwork shown in Figure 7A, except that the front plate and the first back plate are printed in an ink of lower saturation than the ink from the second back plate. The purpose of this is to improve contrast in the transmitted light image when all plates are viewed simultaneously. Composite front, back and transmitted light images are shown in Figure 8B.  Compare to Figure 7A. 

Figure 8B. Composite images from the individual plates shown in Figure 8A. The artwork and “image movement” effect is like the one shown in Figure 7B, except that contrast is lower in the front plate image in reflected light and higher in the transmitted light image. Compare to Figure 7B.

Resisting CYMK Simulation

Designing security documents to resist CMYK (cyan, magenta, yellow and black) digital counterfeiting is a broad topic that will only be explored here as it relates to simultaneous offset.  From part one of this series, the good same-side registration capabilities of digital printing do not extend to front/back registration.  Part two showed how the security of simultaneous offset features can be enhanced by integration with specialty inks (i.e., metallics) and split fountains, which together can force digital counterfeiters to abandon purely CMYK workflows.  In part three the color mockups illustrated many distinctive visual effects but were limited to conventional spot colors that can generally be simulated by CMYK.  This part four paper further considers how specialty inks and split fountains can solve the problem left unanswered by part three, which is design of simultaneous offset features incorporating characteristics that cannot be simulated effectively by CMYK. 

Consider this concept with a white ink example on a white substrate as shown in Figure 9.  In reflected light the contrast between the print and substrate is low, so the white ink artwork is nearly invisible and cannot be copied or scanned like spot color artwork.  Suppose this white ink is relatively opaque, so contrast is higher in transmitted light than in reflected light and two discrete densities are visible depending on whether one or two layers of ink are overlapped (or more, if additional plates were added).  Such a white-only strategy could be used to add a simultaneous offset feature that does not compete with reflected light artwork (intaglio, for example) or features.  Further, the fuzziness of a watermark image and clarity of a white ink simultaneous offset feature could make a distinctive paired feature if placed in proximity or even integrated in a joint design, particularly for highlight watermarks where the thinner paper improves contrast and visibility for an overlapping simultaneous offset feature. 

Figure 9.  Mockup white ink simultaneous offset design with one front plate and one back plate. The white ink shows low contrast with the white substrate surface, so the artwork is difficult to see in reflected light. In transmitted light, this white ink blocks light and produces a darker image than the reflected light images on the front and back. The design of the front and back art produces a two-tone transmitted light image that is lighter or darker based on whether art is on both sides, or only one side.

Expanding on the white ink example, Figure 10 shows a spot color front and white back, so the front art is visible in reflected light but the back art is not.  In transmitted light the white back blocks light but does not contribute color, so this is different from prior examples where the transmitted light image showed increased saturation (i.e., Figure 1) because both sides contribute color.  Further, the white ink could be on the front and the spot color on the back, or both inks could be on one side of the substrate, and the transmitted light effect would be similar. 

Figure 10. Mockup simultaneous offset design with a spot color ink on the front and white ink on the back. In reflected light the front image can be seen, but the back image shows low contrast with the substrate. The design of the back plate artwork affects the transmitted light image in two different ways as the white ink blocks light. First, it makes a star appear in the center where no front plate image is present. Second, it darkens the circle and some of the stripes that are part of the front image.

White ink is just one possible example.  In concept, any ink that is not easily simulated by CMYK could improve the security of a simultaneous offset feature, if it is (or can be made) compatible with offset printing technology.  These might include metallic, iridescent, color shifting, fluorescent, pastel, spot gloss or others. 

Figure 11 shows metallic ink integrated into a simultaneous offset icon.  In counterfeiting Figure 11, the front and back spot color art could be simulated by CMYK but a second printing step would be required to simulate the metallic specular reflectance.  This adds registration and quality control problems to counterfeiting workflows, increases simulation difficulty and provides more opportunities for error.  Besides specular reflection, the metallic ink in Figure 11 also contributes high opacity that makes the simultaneous offset feature easier to examine. 

Figure 11. Metallic ink integrated into a simultaneous offset design in an issued banknote. The contour of the bird on the front is a silver metallic ink. Metallic ink (a consumable) is compatible with simultaneous offset (a hardware printing technology) and their integration into one design is more difficult to counterfeit than either of the two features independently. Additionally, metallic inks with high opacity can make simultaneous offset features easier to inspect. Also compare to Figure 16.

Unlike metallic ink, iridescent and color shifting inks are typically applied by screen (or intaglio), which does not offer the same high registration capabilities or artwork fidelity as simultaneous offset.  Nonetheless, the examples in Figures 12 and 13 show these ink types applied on opposite sides of a sheet.  If these inks could be adapted for offset delivery it might provide opportunities for more integration with simultaneous offset and split fountain printing, as is possible now with metallic inks. 

Figure 12. Iridescent ink on opposite sides of a passport page. In reflected light the iridescent ink is reflective at certain angles, but at other angles is almost invisible and shows low contrast with the paper substrate color. In transmitted light both ink patterns can be seen easily. The contrast of this ink with the surrounding substrate and offset artwork depends greatly on exactly how it is viewed. Compare to the white ink example in Figure 9.  

Figure 13. Color shifting ink on both sides of a passport page, in good register. Color shifting ink is typically applied by screen or intaglio, but if adapted for offset delivery it might play additional roles in resisting digital counterfeiting.

Integrating Split Fountains

Simultaneous offset and split fountains are products of different press hardware and can be integrated together.  Like Figure 2, in Figure 14 the split fountain artwork is the same on the front and back, increasing saturation in transmitted light.  Like Figure 4, in Figure 15 the front and back artwork are positive/negative images, so contrast decreases in transmitted light and the design vanishes. 

Figure 14. A contrast-increasing simultaneous offset design incorporating split fountain printing in an issued passport. The dolphin artwork is mostly the same on both sides, with green at the tail and red at the nose. In transmitted light, saturation within the dolphin is increased and the split fountain remains visible, though fine line detail is lost. Just as in Figure 2, the artwork outside the dolphin is not the same on the front as on the back, so it becomes blurry. Compare to Figure 2.

Figure 15.  A contrast-reducing simultaneous offset design incorporating split fountain printing in an issued passport. Just as in Figure 4, the front and back are designed as negative images of one another such that the artwork vanishes when viewed in transmitted light. Like Figure 14, split fountain printing is integrated into both sides of the design. The transition direction is consistent between the front and back, so saturation is increased in transmitted light. Compare to Figures 4 and 14.

Considering split fountains in the context of contemporary digital counterfeiting, simulating a spot-to-spot split fountain color transition is a technical hurdle for traditional (offset) counterfeiters without split fountain hardware.  But because CMYK can simulate most spot colors and digital devices have excellent same-side CMYK color registration, simulation of a spot-to-spot color continuum is not nearly as hard for digital counterfeiters as for traditional counterfeiters.  Figures 9 through 11 discussed how specialty inks that cannot be simulated by CMYK can add security when combined with the registration features of simultaneous offset.  Taking the case further, incorporating specialty inks with both split fountain printing and simultaneous offset can increase simulation difficulty even more (Figures 16 through 20). 

Figure 16 shows a metallic-to-brown spot split fountain integrated into a simultaneous offset icon.  Simulation of this design without access to a security offset press would be a complicated multistep process prone to multiple registration errors and resulting in a product of limited quality.  The metallic ink specular reflection and good front-to-back register in the simultaneous offset icon discourage purely CMYK digital counterfeiting workflows.  The split fountain prevents the metallic ink from being treated as an isolated artwork element since counterfeiters must not only simulate a gradually fading metallic effect but also register the metallic to the other art.

Figure 16. Metallic ink, split fountain printing and simultaneous offset integrated in a single icon in an issued banknote. The contour of the bird on the front is a split fountain between silver metallic ink and spot brown ink. Just as in Figure 11, the integration of all three of these offset-compatible elements produces a composite greater than the sum of its parts because it forces multi-step counterfeiting workflows and multiple registration and simulation problems, increasing costs and suppressing quality.

Before considering split fountain simultaneous offset integrations with other types of special inks, Figure 17 illustrates an alternative spot-to-clear (or white) split fountain design.  This implementation does not produce the conventional hue change between two spot colors, but instead a gradual analog fade from higher to lower saturation, with two potential benefits.  First, digital scanning and CMYK simulation of lower-saturation colors may result in poor counterfeit color quality.  Second, simulation of the gradual fade by CMYK forces increasingly wider halftone dot spacing as saturation decreases, preventing individual halftone dots from being concealed.  Where saturation is high, the halftone dots overlap one another and are hard to spot but where saturation is low the printer uses fewer dots and spaces them further apart.  The strategy in Figure 17 creates an offset image that is not easily simulated by CMYK and can be more easily detected both with and without magnification. 

Figure 17. On the left: a mockup of an offset split fountain transition between a spot color ink and a clear (or white) ink, creating a fade across the design. On the right: a mockup of a process color simulation of the image on the left. Identifying the colored dots in the simulation is easier in areas of low color saturation where fewer dots are present, and more difficult where the halftone dots overlap in areas of high saturation. This is highly relevant to detection of digital counterfeits with magnification. 

Applying this concept to simultaneous offset design, each side of the icon in Figure 18 contains the same spot-to-clear split fountain artwork described in Figure 17 and resists digital counterfeiting in the same way.  In transmitted light, the split fountain transitions flow in opposite directions, essentially completing one another, and the simultaneous offset icon artwork looks like a flat tone.  This format capitalizes on both the characteristics of the split fountain in reflected light (Figure 17) and the front/back register characteristics of simultaneous offset.

Figure 18. Simultaneous offset feature incorporating spot-to-clear split fountains on both sides. The transitions proceed in opposite directions, so where one side is lighter the opposite side is darker. In transmitted light, the splits complement one another to produce the appearance of a flat tone and the split transitions disappear. In some ways, this implementation is similar to prior examples that showcased opposing front/back artwork, such as Figures 4 and 15. Also compare to Figure 20.

The template in Figure 18 could be adapted in many ways, such as the substitution of white ink and a reversal of the split direction as shown in Figures 19 and 20 or alternating the stripes between a spot-to-white transition and a spot-to-clear transition that would appear similar in reflected light but create a different effect in transmitted light. 

Figure 19. A white-to-clear split on the front only. This is not a simultaneous offset feature because there is no corresponding image on the back. It is presented to illustrate how both white and clear inks might show low contrast with the substrate in reflected light, but in transmitted light the white ink could block light while the clear ink remains transparent. The split fountain creates a subtle fade effect that would only be visible in transmitted light. Compare to Figure 20. 

Figure 20. White-to-clear split fountains on both the front and back are incorporated into a simultaneous offset feature, with each side similar to the split described in Figure 18. The split fountains are configured in the same direction, so in transmitted light the split fountain effect becomes more pronounced instead of disappearing as in Figure 18. This might improve visibility of the simultaneous offset feature if the ability of the white ink to block light is modest. Compare to Figures 18 and 19. 

Figures 17 through 20 showed only a few limited examples involving spot, clear, and white inks.  Imagine substituting metallic, iridescent, color shifting, fluorescent, opaque pastel, spot, or clear gloss inks.  Some examples might include metallic-to-clear, metallic-to-gloss spot or even matte-to-gloss of the same color.  The quantity of combinations and opportunity for design flexibility created by integrating simultaneous offset, split fountains and specialty inks is truly enormous.  This potential sets the stage for discussion of simultaneous offset as a flexible but frequently underutilized security feature capable of much more than is currently asked of it. 

Conclusion

Following on the first three parts of this series, this fourth paper has discussed simultaneous offset concepts relating to contrast, special inks, and resisting digital simulation.  Though each paper examined simultaneous offset from a different perspective, collectively they paint simultaneous offset as an extraordinarily flexible security feature.  Yet in contemporary security documents, simultaneous offset is usually a single tiny icon featuring few visual effects and limited integration with other security features.  Once a manufacturer has the required press capabilities in place, simultaneous offset requires few consumables and could be leveraged as a scalable design feature to play a much greater role in security artwork than is currently done.  Accordingly, the final part five of this series will regard simultaneous offset as the single defining technology responsible for securing the entirety of a document’s offset background artwork, and boundaries will be tested to see how far this technology can be pushed.

Disclaimer: This document represents the opinions of its authors and not necessarily the opinions of the US government. The technologies and strategies described may not be available, appropriate, or manufacturable for all document issuers. The examples shown do not imply anything about the quality of a document, its designer, its manufacturer, or the issuing authority. For informational purposes only.

References:

1 https://platform.keesingtechnologies.com/security-by-design-monochrome-colour-gamut/

2 https://platform.keesingtechnologies.com/security-by-design-security-design-ink-opacity/

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Joel Zlotnick is employed by the US Department of State, Bureau of Consular Affairs, Counterfeit Deterrence Laboratory as a supervisory physical scientist. His current work involves research in security artwork and design techniques in security printing. He is an instructor on counterfeit detection at the US Department of State Foreign Service Institute.

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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.

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Elizabeth Gil is employed by the Homeland Security Investigations Forensic Laboratory as a forensic document examiner. Elizabeth divides her time between conducting examinations on travel and identification documents and testing security documents for vulnerabilities.

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Tyra McConnell is a Forensic Document Examiner at the US Department of State, Bureau of Consular Affairs, Counterfeit Deterrence Laboratory. She provides training on security documents and develops presentations and e-learning courses regarding counterfeit detection.

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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.

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