10 Aug 20237 min readin Forensics & authentication

See Through the Fakes: How Windows in Banknotes Keep Money Safe

Arif A. Mamedov

President and CEO at Regula Forensics, Inc.

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 features are constantly under scrutiny by Regula’s experts.

The Regula team never stops following and analyzing existing and novel security features in all kinds of identity and security documents. We have registered various types of windows in the notes of European countries, Asian states, Australia, the Middle East, and Latin America.

Let's zoom in to reveal how to tell if money is fake by looking through secure windows.

Stay Tuned

We'll deliver hand-picked content from Regula's experts into your inbox

What is the window on money for?

Nowadays, a window in a banknote is an established and reliable security feature that is almost impossible to counterfeit. It’s eye-catching, easily recognizable, and can be checked for authenticity both with and without special equipment.

A banknote of 100 euro
A secure window in 100 euro

A 100 euro banknote from 2019. It contains a so-called “portrait window”, which is unique and can’t be found in any other banknote. This is a see-through diffractive feature that has different visible effects when viewed from the front (euro sign), back (number 100) and in transmitted light (a portrait of Europa).

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 the plastic visible. Paper notes can also contain secure windows, and they are usually generated either at the 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, see-through windows can be left as they are, or they may be framed or covered with some images, vignettes, embossing, metallized coating, etc. Not only do all these elements make transparent windows look fancy and captivate viewers, but contribute to banknote security. 

Read also: Shedding Light on Luminescent Inks: How They Help Detect Fakes

Insights into banknote security technology: Types of secure windows

To authenticate a window and all the elements it might contain, a person needs to look at it directly, rotate the note to see the window at another angle, hold it up to the light, and view on a different background (light or dark). 

Let’s have a closer look.

15,000 Cambodian riel banknote
A secure window in 15,000 Cambodian riel

A 15,000 Cambodian riel from 2019. A clear secure window in transmitted (on the left) and oblique light with an embossed flower on a gray background (on the right).

 50,000 Iraqi dinar banknote
A secure window in a 50,000 Iraqi dinar

A 50,000 Iraqi dinar from 2015. A so-called Varifeye smart window, made of a transparent film in a paper banknote. Its close-up shows the image of a spiral minaret in transmitted light. The image changes in oblique light and on a dark background.

A 500 rupee of the Seychelles banknote
A secure window in a 500 rupee of the Seychelles

A 500 rupee from the Seychelles from 2016. A clear secure Optiks window in transmitted light (on the left) and its opaque version in oblique light (on the right). The image is made with metallized ink on transparent foil.

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 the note so that the window is placed above the area where something is encoded. Like in a Brazilian real, for example:

A 10 Brazilian real banknote
A secure window in a 10 Brazilian real

A 10 Brazilian real, 2000 series. When the red window is placed above the sail of the ship (by folding the banknote), the number 10 shows.

Another wow effect is shown in a secure 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:

A 100 Romanian leu banknote
A window in 100 Romanian leu

A 100 Romanian leu, 2019 series. The diffraction of light reveals the number 100 in the clear window of the note.

However, not all secure 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.

A 1 Malaysian ringgit banknote
A window in a 1 Malaysian ringgit

A 1 Malaysian ringgit note, 4th series. The half window in the upper left shows the image printed on the rear side of the note.

How to authenticate secure windows in banknotes

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 secure window is cut correctly. It will also allow you to define the 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 secure 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 solutions for banknote security feature verification

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 any identity document. And the spectral comparator Regula 4308 and its polarizing filter can help verify the presence of liquid crystals in the film that forms a window in a note.

All the knowledge and data on various security features in documents, accumulated by the experts at Regula over more than 30 years in the industry, have translated into robust Information Reference Systems that assist in the authentication process at border control points, in currency exchange offices, 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 numbers over 7,300 banknotes and coins.

To learn more about various banknote security features, please check Regula’s extensive glossary, which describes them all.

We're Here to Help

Document forensics
for your mission-critical projects

On our website, we use cookies to collect technical information. In particular, we process the IP address of your location to personalize the content of the site

Cookie Policy rules