GLOSSARY
TERM: DEFINITION
Aliasing
See Moiré Pattern.
BEP
Bureau of Engraving and Printing.
Black Light
See Ultraviolet.
Charge Transfer (CT)s
A color-producing mechanism in which the absorption of light produces the movement of one or more electrons from one atom in an ion to another.
Chromaticity Diagram
A three-dimensional array containing all the colors that can be perceived. A simplified two-dimensional section is usually known as the “color triangle.”
Color
The perception in the eye-brain system produced by a non-white distribution of electromagnetic energy. See Appendix C.
Color-Shifting Inks
See Optically Variable Inks.
Covert Features
Security features that are hidden in the banknote and are not intended to be made public. Used by the Federal Reserve Bank for currency authentication and by law enforcement for forensic purposes.
Diffraction
The spreading of light at a sharp boundary. When diffraction occurs from periodic structures, it produces color by interference, as in the colors produced by a diffraction grating.
dpi
dots per inch
Electrophotography
An electrostatic image-forming process in which light, x-rays, or gamma rays form an electrostatic image on a pre-charged, photoconductive, insulating medium. The charged image areas attract and hold a fine powder called a toner, and the powder image is then transferred to paper and fused there by heat.
Electrostatics
The study of electric charges at rest, their electric fields, and potentials.
Embedded Features
Security features that are added during the papermaking process or inserted between laminated layers. They include threads, planchettes, fibers, microtaggants, microcapsules, and so on.
Enhanced Fibers
Fibers that respond to ultraviolet, infrared, or other excitations to give identifiable reactions and are added to paper as a security feature.
Fibers
Dyed fibers embedded in the paper as a security feature. See also Enhanced Fibers.
Fluorescence
See Luminescence.
Hologram
A structure that transmits or reflects light so that a three-dimensional image can be seen. This image appears to move as the viewing orientation is changed.
Hot Stamping
A process in which separate stripes, foils, or other features are applied to the surface of the substrate.
Infrared
Electromagnetic energy beyond the red end of the visible spectrum, that is, with wavelength longer than 700 µm. May be perceived as heat by the skin.
Infrared Inks
Inks containing dyes or pigments that absorb in the region 700 to 1,000 µm.
Ink-Jet Printing
A non-impact priting technique that uses electrostatic acceleration and deflection of ink particles emerging from nozzle to form characters on plain paper.
Intaglio Printing
Characters are formed as depressed areas on the printing plates. These are filled with ink, which is transferred to paper under pressure.
Interference
The constructive reinforcement or destructive cancellation when two beams of light interact. Thus, the beams reflected from the two surfaces of a soap bubble film can interfere to produce colors.
Iridescence
Those interference colors that show a change of color with orientation and are metallic-like in that they have a high reflectivity, as in multiple-layer interference filters on camera lenses.
Kinegram
A special type of surface-relief hologram.
Laminate(s)
A sheet of material made of one or more bonded layers.
Latent Image
See Void Pattern.
Letter Press Printing
Characters are formed by raised surfaces on the printing plates; a roller applies ink to these raised surfaces and the plate is pressed against the paper to transfer the ink.
Luminescence
The production of light when a substance is nonthermally activated as by ultraviolet, electricity, friction, chemically, etc. Also termed “fluorescence,” “photoluminescence,” “electroluminescence,” and so on. Also see Phosphorescence.
Magnetic Printing
Non-impact printing in which the ink contains magnetic particles that control the printing process.
Metamerism
When two different dyes or pigments match in color in one illumination but do not match in a different illumination.
Microcapsules
Small particles, not visible to the eye that are added to substrate and that respond to ultraviolet, infrared may be plastic particles or other excitations to give identifiable reactions.
Microprinting
Printing so small that it is not reproduced by machines with low dpi capability; usually only visible with magnification. Due to the fibrous nature of U. S. currency, there is a limit to the size of microprinting.
Microtaggants
See Microcapsules.
Moiré Pattern
A new pattern formed by the superpositioning of two patterns whose periodicities are not identical. This process is also called aliasing.
Multi-Diffraction Grating
A diffraction grating that produces a shift in the pattern seen on changing the viewing angle.
Non-impact Printer
A line printer in which the characters are produced electrically, electro-optically, or optically rather than mechanically.
Opacity
Nontransparency to light.
Optically Variable Device
Any feature that uses the color-shifting (optically variable) effect.
Optically Variable Inks
Inks that contain thin-film interference filter pigments that produce an iridescent reflection that changes color as the viewing angle is changed. Also known as “color-shifting” inks.
Optically Variable Pigment
The pigment portion of a color-shifting (optically variable) ink.
Overt Feature
A security feature that is visible or apparent without requiring special instruments. May require some instruction on how to observe it. The feature may be particularly visible on the genuine note (a passive visible feature) or may only show after a copy has been made.
Paper
The substrate used in printing currency, usually based on cotton and linen fibers rather than cellulose as in ordinary paper.
Paper Furnish
The fiber-water slurry from which the paper is made.
Phosphorescence
A slow luminescence, which lasts minutes to hours, usually produced in organic molecules and involving “forbidden” triplet to singlet transitions.
Photochromic Inks
Inks containing dyes or pigments that change color when exposed to ultraviolet or very intense visible light. They subsequently revert to their original color.
Photoluminescence
Luminescence produced by exposure to ultraviolet.
Pixelgram
A special type of surface-relief, computer-generated diffractive optical element, based on a discrete-pixel (picture element) addressing scheme.
Planchettes
Colored or reflective pieces of paper or plastic a few millimeters in diameter that are added during paper manufacture.
Scanner
Any device that examines an area or region point by point in a continuous systematic manner, repeatedly sweeping across until the entire area of the region is covered; an example is a flying spot scanner.
Security Thread
The thread present inside the paper used in currency printing. May carry the domination of the bill or may be fully metallized.
Substrate
The medium on which currency is printed. May be paper, plastic, or a laminated combination.
Thermal-Transfer Printing
A technique in which heat transfers a dye or a colored wax from a ribbon onto paper.
Thin-Film Interference Filters (TFIF)
Multiple-layer structures that produce color effects by interference.
Thread
See Security Thread.
Transparency
An image fixed on a clear base by means of a photographic, printing, chemical, or other process, especially adaptable for viewing by transmitted light. (Optics) The ability of a substance to transmit light of certain wavelengths.
Ultraviolet
Electromagnetic energy beyond the violet end of the visible spectrum, that is with wavelength less than 400 µm. Also called black light. May produce tanning of the skin and injure the eye.
Variable-Sized Dot Patterns
Printing with a combination of large and small halftone dots; the larger dots would be above the resolution limit of scanner or copier, while the smaller dots would be below it. The larger dots would be printed in a pattern, such as one spelling “VOID,” which would stand out on the copy, since the smaller dots would not be resolved. A typed “Void Patterns.”
Void Pattern
A security device consisting of a period structure as an overt but not visible feature. When copied on a machine with a different periodicity, the resulting moiré pattern displays the word “VOID” or some other message.
Watermark
A localized modification of the structure and opacity of a sheet of paper so that the pattern or design can be seen when the sheet is held to the light.
