Metamerism: the effect generated when using a pair of similarly shaded inks, the color and contrast of which appear virtually identical in normal light, but which have different spectral responses so that, when viewed with a filter or under special illumination, one displays different effects or colors to the other.

Micrometer: one-millionth of a meter

Micron: a unit of measurement commonly used in authentication when referring to the thickness or gauge of physical substrates and features. One micron is equal to one millionth (10-6) of a meter.

Microprint: print that is so small that it cannot be reproduced by photocopying or scanning, and which can only be read under magnification

Moiré patterns: images formed by the superimposition of two patterns with different periodicities, so that they display different visual effects according to the viewing angle


Nanometer: one-billionth of a meter

Nanotechnology: the science and technology of precisely manipulating the structure of matter at the atomic and molecular level (one nanometer is one billionth of meter) and, in the authentication arena, is being used to explore and develop unique optical phenomena for use in new material and security features.


Offset printing: the technique whereby ink is spread on a metal plate with etched images, then transferred to an intermediary surface such as a rubber blanket, and finally applied to paper by pressing the paper against the intermediary surface. Also known as lithography

Optically variable device (OVD): visible features with dynamic characteristics that change according to the viewing angle – for example from one color to another, or from one image to another

Overt: features that are apparent and visible, and can be viewed without additional readers or instruments.


Phosphorescence: a fluorescence that continues for a period after the stimulus that produced the emission has stopped.

Piracy: illegal reproduction and distribution of copyright material, generally taken to be audio and video content.

Planchettes: microscopic discs made of film or plastic coating features such as UV, IR and even holograms. They can be visible or invisible and are embedded into paper during manufacture.

Polarization: the orientation of light waves into a predominating angle. If all the waves in a beam of light move up and down or from side to side together, the beam is said to be plane-polarized. Some materials have the ability to filter out all light waves except those in a particular direction. Other materials are said to be optically active if they are able to change the angle of a plane-polarized beam of light. Liquid crystals often have this property and this enables them to be detected.

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