Shine Bright Like a Banknote

Counterfeit and altered notes are any collector's worst nightmare. Fortunately, printers are increasingly using different methods of security printing on items of value, such as banknotes, checks, and passports. The main goal of security printing is to prevent tampering or counterfeiting by incorporating features that are not easily replicated into the finished product.

For example: have you ever seen a banknote that glows under ultraviolet lighting?

Luminescence is the emission of radiation by an atom or molecule transitioning from a higher to a lower state of energy. In order to gain a higher state of energy an atom or a molecule absorbs energy through the “excitation” process. The most widely used fluorescent security products emit light in the visible spectrum when excited with longwave ultraviolet radiation.

Fluorescence, in which excitation makes features visible during exposure to ultraviolet lighting, and phosphorescence, in which excitation continues after exposure to ultraviolet lighting has ceased, are the types of luminescence generally used for security features in paper currency. Luminescent substances may be incorporated into a banknote through one of three mediums:

1. Ink - a fluorescent or phosphorescent ink can be made by mixing a luminescent pigment with a binding agent.
2. Fibers - the luminescent pigment can be attached to a polymer to make fibers.
3. Grains - the luminescent pigment can be used as grains that are mixed into the paper pulp.

Fluorescence is frequently used to make the process of counterfeiting more difficult, especially when used in conjunction with other security features. Using a UV light, fluorescent ink can reveal words, patterns or pictures that may be visible or invisible under normal lighting. For instance, some security fibers are invisible in white light, but they fluoresce under ultraviolet lighting.

Australia Pick #63a under UV Lighting Click image to enlarge.

Both US and world banknotes may use fluorescence as a security feature. In US notes, fluorescence is added to the security strip built into the paper. One interesting aspect of genuine US Federal Reserve Notes is that they have a consistent, intrinsic fluorescence lifetime. This allows for detection of counterfeit paper money because of significant differences in the amount of time that security features fluoresce when compared to genuine paper money. In US notes, fluorescence is added to the security strip built into the paper.

Security strip from US $5 bill Click image to enlarge.

To further confound potential counterfeiters, in 1996, US Federal Reserve Notes underwent a redesign and began incorporating a new ultraviolet fluorescent compound into the security strips. This compound, when exposed to ultraviolet light, produces a unique color for each denomination.

Colored Fluorescent Strips on $5, $10, and $20 Federal Reserve Notes Click image to enlarge.

While the security strip alone makes counterfeiting US banknotes more difficult, modern world notes have incorporated fluorescent elements in myriad, increasingly complex ways. Moreover, some hidden security features can be quite beautiful when revealed, as you can see by the following examples:

Fluorescent Designs on a 5 Euro Note, front Click image to enlarge.

Fluorescent Designs on a 5 Euro Note, back Click image to enlarge.

Fluorescent Dragon on a China Pick #902 Note Click image to enlarge.

China Pick #884b “Golden Dragon” Click image to enlarge.

The unique note above is called a "Golden Dragon," a particular variety of the Chinese Pick #884 banknote. When exposed to UV lighting, "scales" across the surface of the banknote glow a bright golden color; by contrast, in other varieties of the Pick #884, those areas remain dull when exposed to ultraviolet light. Currently, it is unclear whether this is a phenomenon resulting from the printing process or an obscure security feature, but the hidden design makes this an enticing piece for many collectors.

So next time you are looking at modern banknotes, remember: they're more than meets the eye.