The last decade has seen a massive emergence of windows in banknotes throughout the world. Transparent, translucent, with transforming or hologram images, and serving as filters, all these security elements are constantly under scrutiny by Regula’s experts. The team never stops following and analyzing existing and novel security elements in all kinds of identity and security documents, have registered various types of windows in the notes of European countries, Asian states, Australia, in the Middle East, and Latin America.
Nowadays, a window in a banknote is an established and reliable security element that is almost impossible to counterfeit. It’s eye-catching, easily recognizable, and can be checked for authenticity both with and without special equipment.
Banknotes with windows may start as a clear sheet of plastic onto which several layers of ink are applied. Windows are made by leaving some sections of plastic free of ink. However, a polymer sheet that forms the core of a banknote may be covered with paper on both sides. In this case, a window is made in the outer layers of paper. It is cut out, which makes plastic visible. Paper notes can also contain windows, and they are usually generated either at a sheet-making stage or are formed by a laser and then filled with some transparent film (using liquid crystals or nanomaterials, for instance).
After being created, windows can be left as they are, or they may be framed or covered with some images, vignettes, embossing, metallized coating, etc. Not only all these elements make windows look fancy and captivate viewers, but contribute to the security of banknotes. To authenticate a window and all the elements it might contain, a person needs to look at it directly, rotate a note to see the window at another angle, hold it up to the light, view at a different background (light or dark). Let’s have a closer look.
Some windows serve as filters – they reveal hidden images, texts or codes printed on the same banknote. To witness this effect, one needs to fold a note so that the window is placed above the area where something is encoded. Like in a Brazilian real, for example:
Another wow-effect is shown in a window that contains a diffractive optical element (DOE) – a so-called winDOE. It visualizes a rainbow hologram image when seen in transmitted light from a point light source (lamp, flashlight, etc.). To get the point, let’s examine a Romanian leu:
However, not all windows are transparent. In some cases, only one side of a polymer substrate of a banknote is left visible, while the other side is opacified. This is known as a half window. It’s glossy where it shows, and the rear side of a note serves as a regular printing surface.
Indeed, examining windows in banknotes can be rather amusing, and anyone can easily see all the tricks with their own eyes. Nevertheless, using special equipment can add to the verification of windows and thus to the authentication of banknotes.
For example, magnification with special devices will show whether the framework of a window is cut correctly. It will also allow you to define a method of printing for a vignette. If a window is created by a laser, magnification will reveal that its edges are correspondingly burnt. So, even if malefactors somehow try to counterfeit a banknote with a window (which is really hard, for example, Australia has not yet come across a single attempt at falsification of such banknotes), forensic devices will show it immediately.
Regula’s latest compact device – Regula 1031 – allows for 24x magnification, and this significantly helps to thoroughly examine the security features of any banknote as well as an identity document. And a spectral comparator Regula 4308 and its polarizing filter can help verify the presence of liquid crystals in a film that forms a window in a note.
All the knowledge and data on various security documents, accumulated by the experts of Regula for over 30 years of their work, have translated into profound Information Reference Systems that assist in the authentication process at a border control point, in a currency exchange office, etc. These systems provide databases of travel documents, banknotes, driver’s licenses, and vehicle registration certificates with a detailed description of their security features.
The “Currency” Information Reference System contains data on 200 currencies that are arranged by country and production series. Overall the database counts over 7,300 banknotes and coins.
To learn more about various security elements in banknotes, please check Regula’s extensive glossary, which describes them all.