Ink
Features
All of the inks used in bank note printing
offer a certain amount of security because they are not commercially
available and hence not available to would be counterfeiters.
The inks used have to have a very high performance and be very resistant
to environmental conditions such as sunlight, heat, moisture, etc.It
would be no good if we accidentally dropped a note in a puddle and
all the ink fell off, or we casually left our money lying around
in the sunshine and all the ink faded away !
Colour
Choice
Surprisingly the choice of colours
in which a note is printed can provide quite a security element.
Many commercial reproduction methods have problems telling some
colours apart for instance colour copiers tend to reproduce lime
green as yellow. Knowing the limitations of technology used in counterfeiting
can enable the bank note printers to add protection in a cheap but
effective way.
Fluorescent
Inks
Materials which fluoresce under ultra
violet light can be added to most inks. They can be incorporated
into a visible design element or an invisible design element (ie
printed as a transparent feature). When viewed under ultra violet
light all is revealed. The following graphic shows what this note
revealed under UV light. The 10 will have been printed as an invisible
feature. Note also the fluorescent fibres in the paper.
Metallic
Inks
Metallic inks produce a sheen effect
when printed as compared to the matt effect seen with other inks.
They are generally used in large areas of solid colour so that their
effect is maximised. They offer good protection from colour copy
counterfeiting.
Metameric
Inks
Metameric inks work on the principle
of metamerism ....two colours matching under one set of lighting
conditions can appear and quite different under another set. The
effect of such a feature can be seen below. Under normal viewing
conditions nothing is apparent but when viewed under a red filter
a numeral appears.
Magnetic
Inks
Magnetic inks enable areas of a note to be read by a magnetic detector.
They are sometimes used for the letterpress component of the bank
note, the serial numbers.
Optically
Variable Inks
Optically variable inks or OVI contain
tiny flakes of special film which changes colour as the viewing
angle is varied. The result is an ink which has this same optical
property, changing colour as the viewing angle is varied. They are
very expensive inks and generally only used in small areas. An OVI
feature is sometimes printed using the silk screen process
They do however offer excellent protection against all counterfeiting
methods.
Iridescent
Coatings
This effect is generally seen as
a band or either solid or patterned design. It is applied by the
silk screen printing process before any other printing is carried
out. The iridescent or pearlised effect cannot be reproduced by
a colour copier and therefore gives good protection from this threat.
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