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IR-FLUORESCENT INKS
Inks containing fluorescent pigments which glow when exposed to blue-green light of 400-530 nm. Luminescence is visible under IR-light of 850-950 nm as bright light images on a dark background (fig.1, 2). IR-fluorescent inks are not perceived with the naked eye in white light. Inks are used for applying design elements, texts or for coloring security fibres, a security thread, a stitching thread, etc.

a	b
Fig. 1. Slovenia. Diplomatic passport: а — page 17 in white reflected light; b — luminescence of a security thread, security fibres, a text and a serial number viewed under IR-light
a	b
Fig. 2. New Zealand. Diplomatic passport: а — central spread with a stitching thread viewed in white reflected light; b — luminescence of a stitching thread and design elements when exposed to light of 400-530 nm. IR-light

IR-METAMERIC INKS

Inks which have similar spectral features in visible light (perceived like of the same color) but different under IR-illumination (some inks absorb IR-light others reflect). As a result, when examining an image with IR-metameric inks only IR-visible parts of the image can be seen on the monitor (fig. 1).

Infrared security features are based on the property of a document material (usually dyes) to absorb or reflect IR-light in different ways. An IR-map of a document is a grayscale image of the document under IR-light of 850-950 nm wavelength. Depending on the level of absorption or reflection the image on the map may be black, gray or invisible (fig. 2, 3).

a	b
Fig. 1. Brunei. Passport: а — back endpaper in white light; b — the same fragment viewed under IR-light: only the part of the text reflecting IR-light is visible

a	b	a	b
Fig. 2. Macau. Passport: а — page 48 in white light; b — the same view under IR-light: parts of the image with the different level of IR-reflection		Fig. 3. Belgium. Passport: а — back endpaper; b — the same view under IR-light: the image is invisible

IRIDESCENT INK

A semi-transparent ink with a pearl luster determined by an interference structure of a thin film. The ink contains mica scaled pigments covered by TiO2, Fe2O3 or other metal oxides placed in the transparent binding medium of the ink (fig. 1).

Fig.1. Structure of an iridescent ink pigment

When falling on pigment scales, a part of light reflects and another part transmits into multilayer scales. As a result multiple reflection and transmission of light by different layers occur and we may observe interference.

A color depends on the thickness of the oxide layer. Brightness and blinking effect are determined by the size of pigments. If the background color is dark and rich it also affects the ink tone. The luster is not seen at a right angle but a sparkle, a slight change of the ink tone or its brightness are observed when changing the angle of observation or illumination (fig. 2).

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c	d
Fig. 2. Thailand. Temporary passport: а — passport spread (front endpaper and page 1) at a right angle; b — front endpaper under oblique light; c, d — flower image covered with the iridescent ink. Light reflected from the dark-blue background colours transparent ink pigments blue. The ink is transparent outside the image. Lines of the background pattern are visible through it

IRIDESCENT LAMINATE

A thin-film coating in the form of a stripe, a text or an image with color changing effect. The effect appears when the angle of observation or illumination changes. The iridescent laminate doesn’t contain ink pigments. It is transparent when viewed at a right angle in diffuse white light. The coating is red under direct incident light at a right angle and becomes green when viewed under oblique light at an acute angle (fig. 1, 2).

An even change of the angle of illumination and observation leads to a color change into medium compound spectral tones. A color changing effect is determined by a thin-film interference.

The iridescent laminate is applied on the inner surface of the laminate on the data page.

Fig. 1. Thin-film interference scheme

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d	e
Fig. 2. Sweden. Official passport: а — spread (data page and page 3); b, c — iridescent image viewed at different angles of illumination and observation; d, e — zoomed image fragments

LAMINATE

A transparent polymer film applied on the substrate over the whole data page or only over its part in order to protect the document against its damage or forgery.

Laminate classification

By surface texture:

• glossy (fig. 3b);
• matt (fig. 1);
• porous (fig. 2).

By fixing method:

• stitched into a passport book (fig. 3);
• not stitched into a passport book (fig. 4).

A laminate can cover a page both from one and two sides. In the second case laminate sheets are solded together in the form of a pocket (fig. 1b). The laminate may have right or rounded angles. It can also incorporate additional security features such as holograms, retroreflective effect, embossing, etc.

a	b
Fig. 1. Azerbaijan. Passport: а — spread (data page and page 2); b — transparent laminate covers the data page from both sides
Fig. 2. Slovakia. Identity card as a travel document. Matt laminate stitched into a passport book
a	b
Fig. 3. Australia. Temporary passport: а — data page. The laminate is not stitched into the passport book; b — porous laminate with the retroreflective effect
a	b
c	d
Fig. 4. France. Passport: а — data page is completely covered with the laminate; b — glossy laminate is stitched into a passport book; c — laminate with the background between pages 14–15; d — laminate stitched in the spine of a passport book
a	b
Fig. 5 Japan. Passport. 2013: а — spread (data page and page 3) (arrows indicate the upper and lower boundaries of the laminate); b — glossy laminate which is not stitched into a passport book: above is a non-laminated part of the data page

LAMINATE OVERPRINT

An image which is applied on the laminate coating to protect it against forgery. Screen printing and gravure printing are the most frequent printing methods used for the laminate overprint (fig. 1).

a	b
Fig. 1. Korea. Travel document: а — spread (pages 2–3); b — laminate overprint fragment: gravure printing

LASER ENGRAVING

Applying an image or a text on a paper or a polymer substrate using the energy of a laser beam. A laser beam heats the surface of a substrate (for example, polycarbonate). As a result carbon deposition occurs in the upper transparent layers. Deposing carbon is visualized in the form of black dots of different tones which form an image. When the laser beam affects a paper surface its discoloration occurs and the ink layer is removed.

Classification

By technology:

• removal of a previously applied layer, for example, an ink (fig. 1, 2);
• removal of the material (appearing of a cut or a trough in the place of a laser beam exposure) (fig. 3b).

By image view:

• monochrome laser engraving occurs when the laser source has no ability to control power (fig. 3c);
• tonal laser engraving is applied in the greyscale by controlling power and speed of the beam (fig. 4b).

By image type:

• vector laser engraving occurs when the laser outlines letters or image contours with thin lines (fig. 3b);
• raster laser engraving takes place when the laser forms a number of different density dots (fig. 4b).

By volume:

• plain (2D) laser engraving is applied on materials with a nontransparent surface (fig. 4c);
• volume (3D) laser engraving is tactile (fig. 4d).

Laser engraving is used in the personalization process for applying a holder’s portrait or personal data, numbers or other security features.

a	b
Fig. 1. Slovenia. Diplomatic passport: а — page 1; b — laser engraving on a paper substrate. Substrate discoloration and slight charring
a	b c
Fig. 2. Egypt. Passport: а — polymer spread (front endpaper and page 1); b — secondary holder’s portrait on page 1 viewed in transmitted light; c — photo fragment in transmitted light. Light dots are a white ink removed by laser engraving. Dark dots are sections left unaffected
a	b c
Fig. 3. Hungary. Passport: а — spread (data page and page 32); b — text (holder’s personal data): trough in the substrate after laser engraving; c — fragment of a holder’s portrait. Amplitude-modulated monochrome raster image. Charring of a polymer substrate after a laser beam exposure
a	b
c	d
Fig. 4. Montenegro. Passport: а — spread (data page and page 3); b — fragment of a holder’s portrait. Tonal image, frequency-modulated raster; c — plain 2D image on the inner layer of the data page; d — concave relief resulted from a polycarbonate surface foamed by a laser. Volume 3D image combined with the underlying plain (c) image

LATENT FILTER IMAGE LFI

LFI — Latent Filter Image

An image which is applied by the slit raster technology. The scene of the image changes when changing the angle of observation. A latent filter image consists of a slit raster printed inside a transparent polycarbonate which serves as an optical filter and a scrambled image stripped from two initial images (fig. 1). Lightness of the image changes regarding to the background when changing the angle of observation. Latent (second) image is visualized at an acute angle of observation and printed by offset (fig. 2).

Fig. 1. Scheme of a latent filter image visualization: 1 — scrambled interlaced image stripped from initial images A and B; 2 — slit raster; 3 — initial images are visualized at different angles of observation
a
b	c
d
Fig. 2. Estonia. National identity card: а — reverse side; b — latent filter image: «EST» abbreviation. View at a right angle; c — the same image. View at an acute angle of observation; d — the same image. Slit raster. View at a right angle of observation

LATENT IMAGE KIPP

(from German kippen — overturn, rotate)

An image formed by parallel straight relief strokes perpendicular to background strokes. The image is almost invisible in incidental white light at a right angle. It is visualized as an achromatic image in sliding white light at an acute angle of observation due to the shadow casted by relief strokes. A background and an image are applied by means of intaglio and are not differ in color and stroke density. An image becomes lighter or darker regarding the background when rotated around the vertical axis without changing the angle of observation (fig. 1).

a	b c
d
Fig. 1. Montenegro. Official passport: а — front endpaper, general view; b, c — latent image KIPP viewed at different angles of observation and illumination; d — the same zoomed fragment: relief strokes of the latent image perpendicular to background strokes

LATENT IMAGE MASK

ИAn image in the form a number of lines or strokes of a certain geometrical shape or raster elements. A latent image makes a whole with the background image in technique, color and printing method. Its contours are slightly visible by the naked eye. Zoomed image is visualized as an alphabet symbol, figure or geometrical figure in white light (fig. 1). Latent image MASK is printed byoffset.

a	b
Fig. 1. Belgium. Passport: а — page 3; b — latent image fragment: «BEL» abbreviation

LATENT IMAGE PEAK

PEAK — Printed and Embossed Anti-Copy

An image is formed by lines of blind embossing in the foreground and parallel straight strokes of the background. The image is almost invisible in incidental white light (fig. 1а). When sliding light is perpendicular to relief lines a shadow is formed and a latent image is visualized on the ridges of these lines (fig. 1b, 1c). When rotating a document around vertical and horizontal axes its different areas become lighter or darker regarding to the background (fig. 1d, e).

a	b c
d	e
Fig. 1. Kosovo. Official passport: а — back endpaper; b, c — latent image PEAK viewed at different angles of observation and illumination; d, e — zoomed image fragments. Lines of blind embossing form a foreground image (d), lines of blind embossing form a background (e)

LATENT MULTICOLOUR IMAGE

An image which is formed by parallel multicolor background strokes or relief lines of blind embossing. A latent multicolor image is slightly visible in white light. It is visualized as a chromatic image under oblique light. Every chromatic element of the image changes its color when rotating the document around the vertical axe without changing the angle of observation (fig. 1). Background strokes are applied by offset, relief lines are printed by intaglio.

a	b	c
Fig. 1. Kosovo. Passport: а — back endpaper; b — latent multicolour image viewed under oblique light; c — the same fragment. View when rotating the document by 90° around the vertical axe (without changing the angle of observation)

LATENT SCRAMBLED IMAGE

Strokes or raster elements of latent scrambled image are embedded in the background or a photo the way that the image is not visible when viewed by the naked eye. The image is previously fragmented and encoded according to special algorithms. A latent scrambled image is visualized by means of the lenticular decoding devices. It is applied by the printer or offset (fig. 1, 2).

a	b
Fig. 1. Bulgaria. Passport: а — data page; b — latent scrambled image printed on the holder’s portrait (personal data). View in a gray gradation. The image is visualized by means of a decoding lens. Printer
a	b c
Fig. 2. Iceland. Passport: а — front endpaper, general view; b, c — latent scrambled image at the top and the bottom of the page. View in a gray gradation. Offset

LENTICULAR TECHNOLOGY

(from Latin lenticula — a small lens)

A method of printing and visualization of an image using lenticular lens. It allows getting an image changing effect depending on the angle of observation. A lenticular is a sheet of a transparent plastic material. The front side of a sheet has a relief surface and composed of parallel cylindrical lenses. The back side is smooth. Scrambled interlaced images are printed under the lenticular. The principle of encoding is that initial images are stripped and joint together the way that at list two stripes (one from one image and the second from the other one) are placed under every lens. Every lenticular acts like a magnifier which zooms and reflects only one of all image stripes depending on the angle of observation. Achromatic or color scrambled images are applied using offset printing or laser engraving.

Fig. 1. Lenticular technology scheme: 1 — initial images А and Б are stripping. The number of stripes is multiple of the number of lenses; 2 — lenticular; 3 — scrambled interlaced image

Fig. 2. Visualization of the image depending on the angle of observation: 1 — scrambled interlaced image stripped from the initial images А and Б; 2 — lenticular. А and Б images are visualized alternatively depending on the angle of observation

LETTERPRESS

A printing technique when ink is applied to a substrate from a printing plate with printing elements raised above spacing elements. The process is carried out under high pressure (at least 15 kg/cm2) with the use of rapidly drying inks.

Characteristics of the print:

• uneven ink distribution in strokes: less ink in the middle than along the edges (fig. 1c);
• a rim formed by the ink along the edges of a stroke (fig. 1b);
• • substrate deformation: protuberance on the back side of a sheet and inward bulging on the front side of a sheet in the area where the print is applied (fig. 1d).

Letterpress printing is often used for printing serial numbers, bar codes, and design elements of covers.

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c	d
Fig. 1. Qatar. Passport: а — page 32 , general view. The number is printed by letterpress; b — fragment of the number: a rim along the edge of a stroke resulted from the ink squeezing out of a printing plate; c — number on the front side of the print: blind spots on figure 8; d — back side: substrate deformaion due to pressure, convex relief

MAGNETIC INK

An ink containing ferromagnetic components, which have a specific reaction to the external magnetic field. Texts or symbols applied by the ink can be identified by special magnetic sensors or visualized by magneto-optic converters. The magnetic ink can be applied on security threads, fibres and used for printing images (fig. 1), serial numbers, bar-codes (fig. 2).

a	b	a b
Fig. 1. Sweden. Alien’s passport: а — front endpaper; b — image and serial number applied with magnetic inks		Fig. 2. Azerbaijan. Small visa-sticker: а — view in white light; b — bar-code applied with magnetic inks

MAGNETIC STRIPE

A medium in the form of a stripe with the limited storage space. A magnetic stripe is usually placed at the reverse side of a card. The data which has previously been coded recorded on magnetic stripes. The data reading process is carried out by using special devices – readers (fig. 1).

Fig. 1. The United States of America. Arizona. Identity card. Magnetic stripe at the reverse side of a card

METALLIC INK

An ink containing a fine-dispersed powder of bronze (fig. 1b) and aluminum (fig. 2b). It has a specific metallic gloss. Only a gloss intensity changes when changing the angle of observation and illumination of the image applied by the metallic ink. Any significant changes in the color are not observed.

a	b	c
Fig. 1. Estonia. Alien’s passport: а — front endpaper; b — image applied by metallic ink viewed at an acute angle of illumination and observation; c — the same zoomed fragment. Fine-dispersed powder of bronze
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Fig. 2. New Zealand. Diplomatic passport: а — page 26; b — see-through register applied with the metallic ink; c — the same image in transmitted light

METAMERIC INKS PAIR

Special security inks (usually the pair of inks) which look similar in one type of illumination (for example, IR-light, UV light, oblique white light) but show a noticeable difference in another type of light.

a	b
Fig. 1. Japan. Passport: а — view in white light; b — view through the orange light filter

MICROPRINTING

Micro images (figures, symbols, texts) of 0,15–0,3 mm height (fig. 1–5). Microprinting is visible only when zooming.

Microtext classification:

• positive (contour) microtext applied by dark letters on a light background (fig. 1b);
• negative (direct) microtext applied by light letters on a dark background (fig. 2b).

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Fig. 1. Ukraine. Passport. Microtext: а — microtext in the form of two lines on the data page; b — the same zoomed image: top line — negative microtext, bottom line — positive microtext

Microtext may be embedded into the image in the document, serve as a background, form patterns and images (fig. 3), increase security features of holograms (fig. 4), security threads, images applied with optically variable ink OVI.

a	b
Fig. 2. Japan. Passport. 2013: а — data page; b — negative microtext (holder’s personal data) embedded into another text, ISO country code
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Fig. 3. Greece. Passport: а — central spread (pages 16–17); b — image fragment applied with microtext. Offset
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Fig. 4. The United Arab Emirates. Official passport: а — data page; b — microtext in the hologram

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Fig. 5. The United States of America. Permanent resident card: а — reverse side of a card; b — microprinting: US presidents’ portraits; c — the same zoomed fragment

MOIRE VARIABLE COLOUR (MVC)

MVC — Moire Variable Color

An image formed by parallel straight color strokes of the background and parallel lines of blind embossing located at an acute angle to one another. A background image is printed by offset. Blind embossing is applied by intaglio. The element looks monophonic at a right angle in incident light. Multicolor (rainbow) moire stripes appear when viewed at an acute angle under oblique light (fig. 1).

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Fig. 1. Russia. International passport: а — page 3, general view; b —MVC element at a right angle of observation; c — the same element under oblique light; d — the same zoomed fragment. View at a right angle of observation

MULTIPLE LASER IMAGE MLI / CLI

MLI / CLI —Multiple Laser Image / Changeable Laser Image

An image applied with the help of the lenticular technology, and changes depending on the angle of observation (flip-effect). The image consists of an array of cylindrical lenses (lenticular) and two scrambled images applied by laser engraving. Images may contain holder’s personal data. Images change with flip-effect depending on the angle of observation.

An array of lenses may be horizontally (fig. 1) and vertically (fig. 2) oriented.

a

b

c	d	e
Fig. 1. Sweden. Temporary passport: а — data page; b —visualization and encoding of an image: 1 — scrambled image located under the lenticular; 2 — lenticular; 3 — initial images А and Б; c — multiple laser image at different angles of observation; d — horizontally oriented lenticular

a
b	c
Fig. 2. Finland. Identity card: а — front side; b, c — multiple laser image at different angles of observation. Vertically oriented lenticular

OFFSET PRINTING

A printing technique which uses a flat plate with printing and spacing elements placed in the same plane. Inks are transferred from the plate to a rubber-blanket cylinder, then to the printing surface.

Traditional offset is an offset with dampening when printing and spacing elements are divided due to their physical and chemical properties. It means that spacing elements are applied by the area of the plate which attracts water, and printing elements are applied by the area of the plate which attracts an ink. Before every inking the printing plate is dampened with water. The water film stays only on spacing elements and they don’t attract the ink. Line images in passports are usually printed by mixed inks and rarely by triade inks (fig. 2).

Characteristics of the traditional offset print:

• the absence of a relief (the substrate is not deformed by pressure);
• an even distribution of the ink in strokes, thickness of the ink layer is permanent;
• paper fibers are visible through the strokes (fig. 1).

Dry offset is an offset without dampening. Silicone is used for a layer of printing elements which repulse the ink at the printing plate. Oil inks and UV-fluorescent inks are used for the dry offset printing.

High offset is a printing method which combines elements of letterpress and offset. An image is transferred from the letterpress printing plate to a rubber blanket and then to the printing surface. Printing pressure is lower than in letterpress and the printing plate does not contact the substrate so there is no concave relief.

Characteristics of the print:

• the absence of the relief and substrate deformation;
• the presence of the same boundary effects as in letterpress but it appears to a less extend (fig. 3).

a	b
Fig. 1. Switzerland. Official passport: а — spread (page 40 and back endpaper); b — background pattern, text, planchette are applied by offset

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Fig. 2. Uzbekistan. Identity document of a minor citizen: а — spread (front endpaper and page 1); b — coat of arms applied by raster offset; c — the same zoomed fragment

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Fig. 3. Sweden. Temporary passport: а — spread (front endpaper and page 1); b — text applied by high offset; c — the same zoomed fragment. The rim, the ink is squeezing out of the stroke edge

ONE-SHEET PAPER (SINGLE SHEET DOCUMENT)

A type of a document construction in the form of a paper sheet of any format, self-adhesive or not. A sheet document may be used as an independent document or may be sticked to the endpaper or inside pages of a document (fig. 1, 2).

a	b	a	b
Fig. 1. Mongolia. Diplomatic courier document (105×148 mm): а — front side; b — reverse side		Fig. 2. Sweden. Temporary passport (209×290 mm): а — front side; b — reverse side

OPTICALLY VARIABLE IDENTIFICATION ELEMENT FEEL-ID

A composite security feature based on colour changing and thermochromic effect. It was developed by Giesecke&Devrient company. FEEL-ID has a multilayer structure: 1) The top layer is made using STEP security feature with liquid crystal pigments; 2) The middle layer is made of thermochromic ink; 3) The bottom layer contains laser-engraved identification information (holder’s portrait, etc.).

FEEL-ID characteristic features:

• its colour changes at different angles of observation and illumination (colour changing effect, STEP element);
• identification information hidden beneath the thermochromic ink layer is revealed when exposed heat (thermochromic effect).

FEEL-ID element structure

a

b

c

d

e

f

Hungary. Passport (2006): а — data page. FEEL-ID element location; b — FEEL-ID element viewed at a right angle of observation and illumination; c — the same image viewed at an acute angle of illumination and observation; d — view through a polarizer: the dark area on the right indicates that the light reflected from the FEEL-ID element is circularly polarized; e — thermochromic effect: when exposed to heat, thermochromic ink becomes transparent revealing the document holder’s portrait; f — laser engraved holder’s portrait on the bottom layer. View in IR 840 nm

OPTICALLY VARIABLE IDENTIFICATION ELEMENT FUSE-ID

A composite security feature with identification information about the document holder. FUSE-ID was developed by Giesecke&Devrient company. It is printed with optically variable ink (OVI) and laser engraved afterwards. The element is produced by a laser beam which moves sequentially over the image background area and leaves the image outline untouched. The laser energy discolors optically variable ink by changing its surface nanorelief and optical features. The image contrasts with the brightened background and looks darker. The image color is determined byinterference effect which appears on the layered structure of ink pigments.

a	b	c	d
Fig. 1. Latvia. Passport: а — data page, FUSE-ID element location; b — document holder’s portrait viewed at a right angle under front illumination; c — the same image viewed at an acute angle of illumination and observation; d — scheme of image formation by laser engraving the background

OPTICALLY VARIABLE INK (OVI)

OVI — Optically Variable Ink

An ink which changes its color unevenly due to the angle of observation and illumination. A color changing effect is determined by a thin film interference of pigments placed in a transparent bounding ink medium. Pigments structure is based on so called Fabry–Pérot filter principle (fig. 1). Selective absorption of white light beams occurs as a result of interference and multiple reflection of beams by two reflective surfaces (AL, Cr) The waves which have not been absorbed determine the ink color that we may observe (fig. 2). Characteristics of the reflected light beam are determined by dielectric layer thickness (MgF2) and by the angle of observation.

Security features may be increased by using a microprinting (fig. 3).

Fig. 1. Cross-section of an optically variable ink pigment. Scheme of a color shift in reflected light: 1 — semi-transparent reflective layer (upper mirror); 2 — transparent dielectric layer; 3 — non-transparent reflective layer (metal pigment, bottom mirror)

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	d
Fig. 2. Sweden. Diplomatic passport: а — front endpaper; b, c — image printed by optically variable inks: view at different angles of observation; d — the same zoomed fragment: scale metallize non-transparent pigments of anoptically variable ink OVI

a	b	c
d
Fig. 3. Czech Republic. Official passport: а — spread (endpaper and page 1); b, c — element viewed at different angles of observation and illumination; d — the same zoomed fragment. Negative microtext

OPTICALLY VARIABLE INK WITH EMBOSSING

A complex optically variable security element. It contains an image printed by an optically variable ink OVI which plays a role of the background for the second image applied by blind embossing.

A dual optical effect appears when viewed at different angles of observation and illumination: a color change of the background image and visualization of the second image due a treatment of light and the shade which appears at the ridges of relief elements. An image which applied by blind embossing is not visible at a right angle (fig. 1).

a	b
c	d
e
Fig. 1. Belgium. Passport: а — data page; b — optically variable ink with embossing. View at a right angle of observation; c, d — the same image at different angles of observation and illumination. Colour and lightness changing effect of an image applied by blind embossing; e — optically variable ink used as a background and blind embossing applied over it

OPTICALLY VARIABLE MAGNETIC INK (SPARK, OVMI)

OVMI — Optically Variable Magnetic Ink

Optically variable ink OVI with the dynamic effect. Ink pigments are oriented with the help of magnetic field — image color changes after changing the angle of illumination and observation. The effect of a bright light stripe movement occurs. The ink is usually applied by the screen printing method and contains ferromagnetic pigments.

a	b
c	d
Fig. 1. China. Passport: а — spread (page 48 and back endpaper); b, c — SPARK element viewed at different angles of observation and illumination. Dynamic effect of a bright light stripe movement; d — visualization of magnetic features of the ink.

OPTICALLY VARIABLE PRINTED IMAGE DYNAPRINT

An image applied by the lenticular technology. Dynaprint consists of an array of cylindrical lenses (lenticular) and two scrambled images printed by offset (fig. 1). Color, brightness and contrast change relatively to the background depending on the angle of observation.

a	b
c	d	e
Fig. 1. Estonia. Identity card: а — reverse side; b — scheme of DYNAPRINT visualization: 1 — scrambled image; 2 — lenticular; 3 — initial images А and B; c, d — DYNAPRINT at different angles of observation (the plot of the image doesn’t change); e — lenticular

ORLOV PRINTING

A method of a single-run multi-color printing invented by Ivan Orlov in 1890 in Russia. The Orlov printing is the formation of separate ink layers on color-separated plates and the transfer of the inks to the common plate and then to the receiving surface. In an Orlov printing machine a print is transferred from a plate directly to a paper sheet. In modern devices, an intermediate rubber cylinder (similar to the offset one) is used.

Charactirisics of the print:

• absence of a paper deformation appeared due to a printing plate pressure (for flat printing methods;
• even distribution of the ink in strokes, constant ink layer thickness;
• clear, sharp gradation of colors in strokes without breaks, shifts and overlapping (fig. 1).

a	b	c
Fig. 1. Russia. Passport: а — spread (pages 4–5); b, c — background fragments applied by the Orlov printing

PASSPORT

This is the main document that certifies the identity and gives a right to cross the border. A passport is issued to all individuals who are citizens or permanent residents of a corresponding country. A passport is a small book with a hard or a soft cover. It contains identifying information, security features, holder’s personal data, information about the issuing country and the issuing authority, blank pages for visas and other marks. Every country usually issued several types of passports: a national passport, a diplomatic passport, a service passport, an official passport, an alien’s passport, etc.

There are the following types of passports according to the way of personalization and data processing:

• passport without a machine-readable zone and an electronic medium (fig. 1);
• passport with a machine-readable zone which contains a machine-readable data. This data consists of a combination of figures and letters which according to the international machine-readable travel documents standards must include the main data of the document (fig. 2);
• • passport with an electronic medium (biometric passport) contains a microchip. The secured graphic and text data about the holder of the document is stored in the chip. A special logo in the form of a microchip is placed on the cover of a biometric passport (fig. 3).

Fig. 1. Haiti. Passport. Data page without a machine-readable zone

Fig. 2. Oman. Passport. Data page with a machine-readable zone

Fig. 3. Poland. Diplomatic passport. The cover of a biometric passport

PASSPORT BOOK

A type of a document construction which consists of a folded block of sheets stitched in the spine. It is binded with the help of endpapers or other techniques and then cut from three sides. Additional elements of a passport book are inserts.

PERFORATION

Holes in the substrate, which are located in a certain order. They can form a pattern (a holder’s portrait, a document number, etc.). There are laser (fig. 1, 2) and mechanical (fig. 3) perforation.

Laser perforation

Holes are created by a laser beam. They have a regular form, smooth edges and no raised edges on the reverse side. If several sheets are perforated simultaneously a conical decrease in size of the perforated holes is observed when viewed from front to back. Edges of a hole are slightly charred due to a laser beam exposure (fig. 2b).

Holes can vary according to a size and a shape. The density of perforated holes may vary. Laser perforation is used when applying:

• personal data, secondary holder’s image (fig. 1);
• document number (fig. 3);

If an image is perforated at an angle to the surface it is observed when tilting the page.

a	b	c
Fig. 1. Sweden. Passport: а — data page, polymer substrate; b — secondary holder’s image. Laser perforation viewed in transmitted light; c — Shape of holes viewed in transmitted light

a	b
Fig. 2. Australia. Passport: а — spread (insert 1 — data page and insert 2); b — document number is applied by laser perforation: charred edges. Paper substrate

Mechanical (needle) perforation

Holes are made using the pressure of tubular metal needles. The edges of holes have ridges (“burrs”) which are tactile from the back of the substrate.

a	b	c
Fig. 3. Djibouti. Diplomatic passport: а — page 24. Paper substrate; b — number is applied by mechanical perforator: marks of a mechanical exposure (concave relief on the front side); c — reverse side of holes: burrs, convex relief, paper fibers at the hole edges)

PHOTOCHROMIC INK

An ink containing photochromic pigments which change their color from transparent to red, yellow, blue, purple when exposed to UV light. When the UV light source is removed the image becomes pale and reverts to its original state (fig. 1). This process can be repeated an endless number of times.

a	b
c
Fig. 1. United Nations. ID card: а — data page in white light; b — the same image exposed to 365 nm UV light; c — image printed by the photochromic ink. Ink fluorescence is observed some time after the UV light source is removed. View in white light

PHOTOGRAPHIC PROCESS

A visual image made by means of an optical device on a light-sensitive film and transferred to the photographic paper by chemical process. A photographic paper is covered by light-sensitive emulsion which contains silver bromides size less than 0,001 mm. Small silver particles appear on the areas of the emulsion which were exposed to light after a chemical treatment. They look like dim non-transparent spots which form dark areas. Areas which have not been exposed to light become light and transparent after development.

Characteristics:

• uneven structure formed by random clouds of small dye spots;
• smooth gradation and absence of a raster (fig. 1c, 1d).

a	b
c	d
Fig. 1. Belarus. Passport: а — data page; b — holder’s portrait sticked to the data page; c — the same zoomed fragment. Uneven image structure formed by blot-shape colour elements; d — zoomed fragment of the area where photo is sticked to the background

PLANCHETTES

Thin round or many-sided pieces (scales) of 1-4 mm size which are made of polymer material. Planchettes are embedded into the substrate surface during the paper manufacturing process. They are placed randomly or located in a certain place of a sheet. Planchettes can be colorless, colorful, luminescent under UV light (fig. 1) or have the holographic effect. (fig. 2).

a	b
c
Fig. 1. Australia. Passport – travel document. 2008: а — page 19; b — colourless planchettes viewed in white light; c — the same fragment viewed in UV light of 365 nm
a	b
Fig. 2. The United States of America. Passport: а — data page, general view; b — planchettes with the holographic effect

RAINBOW PRINTING

A special security printing method using a technique in which two or more inks are applied on one printing plate. The printing is carried out with several inks from one color box divided by plates. Special rollers with fixed axial displacement in horizontal and vertical directions are used for printing (fig. 1, 2).

Characteristics of the print:

• equal ink distribution over the surface of a stroke;
• gradual color change when inks are merging into each other.

a	b
Fig. 1. Switzerland. Official passport: а — page 1, general view; b —image applied using a flood fill method. Rainbow printing
a	b
Fig. 2. Russia. Official passport: а — central spread (page 18–19); b — background fine-line pattern. Rainbow printing

RETROREFLECTIVE COATING

An optical device with the retroreflective effect. It consists of several layers (fig. 1):

• retroreflective layer with microlenses (microspheres);
• graphic image layer;
• reflecting layer.

Fig. 1. Retroreflective device scheme: 1 — upper layer with microlenses; 2 — image layer; 3 — reflecting layer; 4 — substrate

When the surface is illuminated by parallel direct (coaxial) light beams, light semi-transparent images which are contrasting with the background are visualized (fig. 2). Microspheres focus light beams on the surface of the reflecting layer the way that reflected light returns towards the light source providing a clear visual perception of the image.

a	b
c	d
Fig. 2. Netherland. Travel document: а — data page viewed in white reflected light; b — retroreflective image viewed in special light; c — transparent laminate coating consisting of microlenses (microspheres); d — substrate structure, cross section

RIP CUTS

A partial cutting of a substrate upper layer or a laminate coating which prevents a structural damage of a document made with the purpose of its forgery.

a	b	c
Fig. 1. Korea. Passport: а — data page; b, c — rip cuts over a laminate coating

SCREEN PRINTING

A printing technique, which enables to obtain an image by pushing the ink through the printing plate. The printing form is a frame made of a silk, synthetic fabric or metal threads. Spacing elements are covered by a layer which does not transfer an ink. Printing elements are open. A thin ink layer is evenly pushed through them by a rubber or polymer squeegee on the printing material during the printing process. This technique is used for printing images which don’t contain thin lines or small details.

Characteristics of the print:

• the absence of pressure and substrate deformation;
• a thick ink layer;
• zigzag or uneven edges of the image (fig. 1).

a	b	c
Fig. 1. Slovakia. Travel document: а — data page; b, c — images printed by screen printing

SECONDARY HOLDER’S IMAGE

A secondary (reproduced once or twice) image of a holder’s portrait which is reduced in contrast and/or size. The image is usually printed using a different printing method than the one used for applying holder’s portrait. It can be located on the data page or other pages of a document.

The main techniques used for applying secondary image:

• laser perforation (fig. 1);
• laser engraving (fig. 2);
• laser printing (fig. 3);
• hologram (fig. 4);
• demetallisation (fig. 5);
• transparent UV-fluorescent inks (fig. 6).

a	b
Fig. 1. Sweden. Identity card: а — front side; b — secondary image, laser perforation. View in transmitted light

a	b	c
Fig. 2. New Zealand. Diplomatic passport: аа — data page; b — secondary holder’s image in a clear window. View against the light; c — the same zoomed fragment. Laser engraving
a		b
Fig. 3. Cuba. Official passport: а — spread (front endpaper and data page): seven holder’s images. Laser printing; b — zoomed holder’s image

a	b
Fig. 4. Germany. Passport: а — data page; b — secondary holder’s image: hologram on transparent substrate
a	b
Fig. 5. Russia. Passport: а — data page; b — secondary holder’s image: laser demetallisation
a	b
Fig. 6. Korea. Passport: а — data page; b — secondary holder’s image: UV-fluorescent ink. View in UV light of 365 nm

SECURE CORE PRINT (SCP)

An image (pattern, alphanumeric characters, etc.) located on the inner layer of a multilayer polycarbonate card with holder’s data. It is printed with special inks by a printing method. Secure core print is visible in transmitted light.

a	b	c	d
Рис. 1. Latvia. Passport: а — data page under white light; b — the same image. Location of secure core print. View in transmitted light; с — the same image. Zoomed fragment; d — structure of the polycarbonate card with secure core print

SECURITY FIBRES

Fine visible or invisible fibres located randomly in the paper substrate. Fibres are embedded in the paper during its manufacturing process and distributed among other fibres of the paper pulp.

Security fibre classification:

By a perception degree with the naked eye:

• visible (fig. 1);
• invisible (fig. 2e, f).

By color:

• monochrome (fig. 1);
• two-color or multicolor with alternating areas of different colors (fig. 2c, d).

By presence of special security inks:

• UV-fluorescent;
• IR-fluorescent.

Fig. 1. Liechtenstein. Passport. Visible coloured (yellow and red) security threads
a	b
c	d
e	f
Fig. 2. Great Britain. Passport: а — page 3 in white light: visible fibres are located at the bottom of the page; b — the same fragment viewed under UV light of 365 nm: visible and invisible security threads; c — visible two-color fibres in white light; d — the same fibres under UV light; e — invisible security fibre in white light; f — the same fibre under UV light of 365 nm
a	b
Fig. 3. Kosovo. Diplomatic passport: а — back endpaper in white light; b — IR-luminescent security fibres

SECURITY THREAD

A narrow polymer-based stripe embedded in a paper web during the paper manufacturing process.

Security thread classification

By arrangement in the paper:

• latent security thread is completely embedded in the paper and visible in transmitted light only (fig. 1–3);
• window (diving) security thread appears partially on the paper surface (fig. 4, 6).

By material and security features:

• simple polymer (fig. 1);
• with a microtext (fig. 2);
• metallized with a color change effect (fig. 3);
• with the «floating» Motion image — when changing the angle of observation the effect of the image movement is observed on the security thread (fig. 4).
• UV fluorescent (fig. 5);
• IR fluorescent (fig. 6).

a	b	c
d
Fig. 1. Poland. Passport: а — page 1 in reflected light; b — latent security thread without a microtext viewed against the light; c — the same zoomed fragment; d — security thread, view in the cross section of the paper
a	b	c
d
Fig. 2. Kosovo. Diplomatic passport: а — page 17; b — latent coloured security thread with a microtext viewed against the light; c — the same zoomed fragment; d — security thread in the paper substrate

a	b	c	d
e
Fig. 3. Russia. Passport: а — page 45, general view; b — window security thread in transmitted light; c, d — the same thread: a color change effect at different angles of observation; e — the same zoomed fragment: paper fibres, where the thread appears on the paper surface

a	b	c
Fig. 4. Sweden. Temporary passport: а — page 3; b — window security thread with the Motion effect viewed in transmitted light; c — the same zoomed fragment. Planes are moving diagonally. View in reflected light

a	b	c	b
Fig. 5. Zambia. Diplomatic passport: а — page 48 in white light; b — UV fluorescent security thread with a microtext		Fig. 6. Italy. Diplomatic passport: а — page 48 in white light; b — security thread with IR fluorescent areas

SEE-THROUGH REGISTER

An image, a part of which is printed on one side of a sheet and the other part on the other side. When the sheet is viewed against the light, both parts match up and create a complete image without overlapping and gaps. A completed scene can only be viewed in transmitted light (fig.1). The image is printed in one pass.

a
b	c	d
Fig. 1. Serbia. Official passport: а — central spread (pages 16–17); b — front side of a see-through register on page 17; c — reverse side of the same image; d — view in transmitted light

SELF-VERIFYING FILTER

A transparent part of a multipage document which allows visualizing latent images, texts or codes located on an adjacent page of the document. During the verification process the filter is placed closely to the image area and scrambled data becomes clearly visible.

A self-verifying filter may have the form of a clear window in one of document pages or can be located on a transparent polycarbonate insert stitched into a passport book (fig. 1).

a	b	c
Fig. 1. Belgium. Passport: а — data page and insert with a self-verifying filter; b — self-verifying filter placed on the holder’s portrait; c — latent scrambled image (personal data), visualized with the help of the filter

SLIT RASTER TECHNOLOGY

A method of printing and visualization of images using a slit raster which allows getting an image changing effect depending on the angle of observation. A slit raster (optical analog of alenticular) is a transparent film on which a pattern is printed. The pattern consists of parallel transparent and non-transparent stripes. A scrambled interlaced image is printed under the slit raster (principle of coding is the same as in lenticular technology).

Depending on the angle of observation only one of stripes of the encoded image are visible through transparent stripes of the pattern. Non-transparent stripes blocked up the other stripe. Images are printed by offset or laser engraving (рис. 1–2).

a	b
Fig. 1. Slit raster technology scheme: 1 — initial images А and B divided on a number of stripes which is multiple of a number of lenses; 2 — slit raster; 3 — scrambled interlaced image	Fig. 2. Scheme of image visualization at different angles of observation: 1 — encoded image; 2 — slit raster. Images А and B are visualized alternatively at different angles of observation

SPINE

The edge of a book block where all elements of a passport book are stitched.

a	b	c
Fig. 1. Ireland. Passport. 2013: а — front side of a cover; b — central spread with a stitching thread; c — the same, top view

STAMP (SEAL)

A seal, an impression, a mark or a relief formed on a paper substrate by means of a stamp pressure.

Types of stamps according to the application method:

• wet stamp is plain and applied with an ink (fig. 1);
• dry stamp is relief and applied without an ink (fig. 2).

Dry relief stamp is viewed under oblique light and perceived by touch. Substrate deformation is observed on both front and reverse sides (fig. 2c, d).

a	b	c
Fig. 1. Azerbaijan. Passport: а — spread (pages 4–5); b — wet colourful stamp; c — the same zoomed fragment

a	b
c	d
Fig. 2. Vietnam. Official passport: а — data page; b — dry relief stamp viewed in side light; c — the same zoomed fragment; d — reverse side of the stamp: paper substrate deformation, relief made by stamp pressure

STITCHING THREAD

A material that is used for holding together the pages of a book block (fig. 1–4). A stitching thread consists of single threads, so called filament, twisted or stuck together. Stitching threads may vary on a number of threads, color, formation method and material. Synthetic threads with additional security features (luminescence in UV and IR-light, etc.) are usually used for stitching of passports and travel documents.

A stitching thread seam is a succession of stitches placed at regular intervals. There are following types of a seam in passport books: regular, complex double or triple stitched seams. Last stitches can be sewn several times.

a	b	c
Fig. 1. Belize. Diplomatic passport: а — spread (pages 24–25), stitching thread; b — simple colourless single-component thread: three last stitches are sewn twice; c — stitching thread: green luminescence in UV light of 365 nm
а	б	в
Fig. 2. Kyrgyzstan. Passport: а — central spread; b — two-colour thread in white light; c — the same thread luminescent in UV light of 365 nm
a	b	c
d		e
Fig. 3. Georgia. Travel document: а — central spread (pages 16–17); c — two-color twisted two-component thread. The last top and bottom stitches are sewn twice; c — IR-luminescent thread; d, e — UV-luminescent thread (365 nm)
a	b	c
Fig. 4. Denmark. Alien’s passport: а — central spread (pages 16–17); b — polymer stitching thermo-thread; c — the same zoomed fragment

SUBSTRATE

A special material used to produce documents, a background for applying images and embedding of security features.

Main types

Paper is a thin (4–400 mcm) sheet consisting mainly of specially treated small bounded and stitched plant fibers. A special paper is used for printing documents and securities. It contains such security features as watermarks, security fibres and threads, etc. Usually paper doesn’t luminesce in UV-light, contains special supplements and chemical components which prevents mechanical and chemical erasures and other types of forgery.

Photographic paper is a nontransparent material on a paper substrate with light-sensitive chemicals which is used for making positive photo image.

Polymer substrate is an acrylonitrile butadiene styrene, polyester, polycarbonate, polyvinyl chloride.

Fabric is a natural, synthetic, carton, denim or other coating materials which are used for producing document.

THERMOCHROMIC INK

An ink which changes colour or becomes transparent at a certain transition temperature. Thermochromic effect is caused by changes in chemical composition or physical properties of thermosensitive pigments. Thermochromic ink may have more than two colour transitions depending on a certain transition temperature. It is applied by offset, letterpress or gravure printing on paper or polymer substrate.

There are two types of thermochromic inks:

• reversible inks change colour when they are heated to a temperature equal to or above the transition temperature. They return to the original colour when cooled to below their critical temperature;
• irreversible inks do not return to the original colour after cooling. It is caused by irreversible chemical or physical changes that take place when the ink is heated.

a

b

c

d	e	f	g	h	i
Ireland. Diplomatic passport (2013): а — data page, location of the image printed in a reversible thermochromic ink; b — image viewed at room temperature; c — thermochromic effect observed when the image is heated to 30-40 degrees: change in transparency; d — passport spread (page 6-7), location of the image printed in reversible thermochromic ink; e, f, g — colour change (grey-green-yellow) when the image is heated to 40 degrees; h — thermosensitive ink pigments before heating; i — the same image heated to 40 degrees

THERMOGRAPHIC PRINTING

Thermographic printing (raised printing) is a post-print technology of producing a tactile raised print. The area printed by offset is dusted while wet with low-melting powder which sticks to the ink. The excess powder is removed from non-printed areas by shaking off or blowing off. Then the substrate is heated, and, as a result, the powder melts and forms a raised relief (raised ink) on the substrate. The powder that is used in thermography can be transparent, glossy or matte. Besides, transparent powder may be combined with metallized pigments or dyes of different colours.

a	b
Moldova. Temporary travel document: a — front side, location of the text fragment printed with thermochromic ink; b — REPUBLICA MOLDOVA text is produced by thermographic printing. Tactile glossy relief is created by melted transparent powder

THIN-FILM INTERFERENCE

Thin-film interference is a phenomenon of two or more light waves superposition which causes their mutual amplification or reduction depending on how the phases of these waves are related to each other. A light beam 1 with a wavelength (λ) falls on the film at an angel (α) and is reflected at the point A. A light beam 2 travels in the film, is reflected from its lower boundary at the point B, is refracted at the point C and returns into the air (fig.1). The path difference appears between two adjacent reflected beams 1 and 2. A light beam 1 passes the distance equal to the interval ABC multiplied by the refractive index (n). But at the point C a part of the light beam is reflected down again, at the point В1 is reflected up, etc. Thus the connection of many waves occurs as a result of consequent reflections of incident light from the lower boundary of the transparent film. This calls multiple beam interference.

If the interval ABC is a whole number of wavelengths, their peaks and troughs will coincide and amplification of all the reflected waves will occur (interference maximum). When the film is illuminated by white light, consisting of waves of different frequency and length, light is refracted at the boundary between the media, and a part of the spectrum is eliminated. The interference maximum occurs for a specific wavelength (red, green or blue) at a certain film thickness and angle. In reflected light the film will have a color corresponding to a certain wavelength. This phenomenon is called “colors in thin films”.

Fig. 1. Multiple beam interference scheme: λ — wavelength of incident light; α — angle of incidence; β — refraction angle; n — refractive index; h — thickness of the film. Conditions of the interference maximum: coincidence of peaks and troughs (phase) of waves 1, 2, 3

Fig. 2. Colours in thin films. The interval ABC is equal to the length of a red light — interference maximum is achieved, phases of reflected and refracted waves are equal. The film is coloured red

TRAVEL DOCUMENT

An official document issued by a state or an organization which is used by its holder for traveling to different countries and contains the obligatory visual inspection data.

Machine-readable travel document (MRTD) is also contains the obligatory brief data in the form which can be read and verified by machines.

Types of documents:

• passport;
• visa;
• official identity document.

UV-FLUORESCENT HI-LITES

Small colored or colorless particles of a different size randomly embedded in the paper during the manufacturing process. The particles glow when exposed to UV light (fig. 1).

a	b	c
Fig. 1. Greece. Alien’s travel document: а — page 1, view in white light; b — view in UV light of 365 nm; c — UV-fluorescent hi-lites, view in UV light of 365 nm

UV-FLUORESCENT INK

An ink containing color luminophores which transmit UV light into fluorescent light of different colors when exposed to UV light (250-380 nm). UV-fluorescent ink is not visible in white light by the naked eye. The ink is used for printing texts, images, secondary holder’s images or for dyeing security fibres, security threads, stitching threads (fig.1).

a	b
Fig. 1. Kosovo. Passport: а — data page viewed in UV light of 365 nm; b — the same page viewed in UV light of 254 nm

VARNISH COATING

A transparent 20-40 mcm thick film which is invisible by the naked eye at a right angle. It protects the substrate from getting wet and prevents ink erasure. Varnish coating is visualized as a coating with slight gloss visible at an acute angle. It is applied over a printed image or creates an independent colorless image.

a b

Fig. 1. Belgium. Vehicle registration certificate: а — outside spread of a booklet; b — varnish right-angled coating covering the right part of the number «714980» applied by letterpress

VISA

A permission to enter the territory of a country. Can be in the form of a sticker with a multilevel security system, an insert, a stamp or a small sticker. A visa is placed on special pages of a travel document. There are machine-readable (fig. 1а) and non-machine-readable (fig. 2, 3а) visas. Images may be printed using a printing method (fig. 1c), digitally printed (fig. 1b) or stamped (fig. 3b).

a	b	c
Fig. 1. Belarus.Passport. page 6: а — machine-readable Schengen visa in the form of a sticker; b — fragment of a holder’s portrait applied with an inkjet printer; c — fragment of a sticker visa. Intaglio

	a	b
Fig. 2. Turkey. Non-machine-readable visa (sticker)	Fig. 3. Philippines. Non-machine-readable visa (stamp): а — position on page; b — stamp fragment

Machine-readable visas may be of two sizes:

• А size — full size — sized to completely fill a passport visa page;
• В size — small size — sized to maintain a clear area on the passport visa page adjacent to the visa to allow, for example, a seal to be placed on the visa and the passport page on which it is affixed or to allow reading a perforated number on passport pages.

WATERMARK

A paper security feature which is visible in transmitted light as an image with slightly blurred, indistinct outlines and a smooth gradation of tones appeared due to local differences in paper density. A watermark is formed on a wet paper web in the process of paper production. It is formed by the density of fibres on certain areas of an image. Darker elements of a watermark are located on the more dense areas of paper. Lighter elements are located on the less dense areas.

Watermark classification

By location:

• General (UNPOSITIONED) watermark is an image repeated at regular intervals all over a document page (fig. 1);
• Local (POSITIONED) watermark is an image located in a certain place of a document page (fig. 2).

Fig. 1. Romania. Temporary passport. General watermark

Fig. 2. Slovenia. Diplomatic passport. Local watermark

By general paper tone:

• Single tone watermark consists of dark or light elements of an image compared to a general paper tone (fig. 3);
• Duotone watermark consists of dark and light elements of an image compared to a general paper tone (fig. 4);
• Multi-tone (halftone) watermark consists of dark and light elements of an image compared to a general paper tone which are gradually transforming into each other (fig. 5).

Fig. 3. Greece. Passport. 2011. Single tone watermark

Fig. 4.Israel. Passport. 2011. Duotone watermark

Fig. 5. Czech Republic. Passport. 2011. Halftone watermark