Security Threads in Banknotes

Peter Symes

With the increasing diversity of new security features in bank notes—such as optically variable devices, micro- printing and light sensitive inks—it is perhaps timely to look at the history of the ‘security thread’, one of the most successful and enduring security features in modern bank notes.

The idea of embedding a foreign material in bank note paper has been around for many years—one of the earliest attempts being made by Benjamin Franklin. For a period of time Franklin was a printer, and printed notes for some of the American states. In an attempt to increase the inimitability of the notes, he manufactured paper with crushed mica embedded in it. J.M.Wilcox of Philadelphia continued this tradition by patenting his ‘Wilcox’ paper around 1860—his paper having blue jute fibres scattered in a vertical strip in the paper.

The use of embedded fibres continues today, usually with the embedding of natural materials such as silk and jute. However there are variations on the type of scattered materials and these include fluorescent fibres, planchettes, and printed colour strips. Whilst it was natural for the development of scattered fibres to continue, it was only a matter of time before someone would introduce a continuous fibre into the paper. The first attempt to do just that can be seen in the 1871 issue of ‘El Banco de Espana’. In this issue we see a worsted fibre that is used in exactly the same way as our modern security threads. The use of the worsted fibre seems to have been for the single issue, but several years later in 1895, another issue of ‘El Banco de Espana’ had a continuous ‘bandage’ of woven red and blue threads appearing on the front of the note. Apparently both these ideas from Spain were ahead of their time, and the Bank did not continue with the use of either device.

The modern security thread was developed in the 1930’s as a joint project between Stanley Chamberlain of the Bank of England Printing Works and Messrs Portals Ltd—the supplier of bank note paper to the Bank of England. The result of their research and development was the metallic security thread known as the ‘Chamberlain’ thread and this is the security thread that most of us are familiar with. The Bank of England first used this thread in their £1 and 10 shillings issues of 1940; however it is probable that the first use of the metallic thread was in the one pound issue of South Africa dated 19.9.1938. This appears to have been a trial use of threaded paper supplied by Portals, as only series A78 of the issue was printed on the new paper, and subsequent issues did not have the thread.

The Bank of England welcomed the arrival of this new security feature, as the years immediately following gave them some concern with the discovery of the German forgeries of their ‘white’ notes. The quality of the forgeries were such that on their detection, the Bank of England determined to introduce the new security feature to the higher denominations. Consequently the £5 notes (‘white fivers’) were issued with metallic threads from 1944.

Because of the Bank of England’s relationship with Portals, or because the patent for the metallic thread was held by Chamberlain, or possibly because of the cost of the paper, the immediate adoption of metallic threads by note issuing authorities was not universal, despite its obvious attractions. However, after a period of time. more and more bank notes were being issued with the new security feature. The Clydesdale Bank in Scotland introduced metallic threads in their issue of 1950, with many other countries following suit in the ensuing years. By the time Australia introduced decimal currency in 1966 the metallic thread was quite common around the world.

When the metallic thread was first introduced it was probably made of steel—indeed it is often referred to as the ‘steel band’. However the type of steel used is a closely guarded secret, as it must be flexible enough to avoid the tearing of the paper and stable enough not to cause deterioration of the paper. One interesting exception to the initial use of steel threads were the bank notes of Saudi Arabia—they used silver threads. This interesting alternative was chosen by the Saudi government because until the issue of their bank notes, their economy was backed by silver coins and silver reserves, and they wished to retain a link with their silver standard.

Not satisfied with the development of the security thread as a single ribbon of metal embedded in paper, the developers of security features worked hard in trying to enhance the properties of the threads. One of the most obvious changes to the threads, is the use of synthetic materials rather than metal. The use of synthetic materials has led to some interesting developments in the production of security threads—which we will look at, each in turn.

One development is the ‘Morse code’ thread, such as is found in the issues of the Bank of Scotland since 1968 and the issues of Kuwait from 1960 to 1968. When held to the light, the security thread is not solid, but is broken into a series of short and long solid sections separated by translucent sections. When the solid sections are interpreted as the ‘dots and dashes’ of Morse code they spell a particular word or phrase. The notes of the Bank of Scotland have the letters BOFS (for `Bank OF Scotland’) and the notes of Kuwait have KUWAIT spelt in their threads.

A simple variation on the Morse code thread is the ‘broken’ thread—which can be seen on the latest issues of the Philippines. This thread has the solid and translucent sections like the Morse code thread, but the solid and translucent sections are uniform in length.

Another development of the security thread is the ‘micro-printed thread’. In most cases, micro-printing occurs on the synthetic threads, and the micro-printing can be observed by holding the bank note to a strong light. With normal eyesight the micro-printing takes on various aspects, from that of a ‘chain’, to small dots, to the likeness of a poorly produced metallic thread—depending on what has been written. and the quality of the printing.

When magnified under good light, it is possible to read the micro-printing. The contents of the micro- printing vary, from the initials of an authority—such as the `UAE’ that appears on the latest issue from the United Arab Emirates, and the ‘12B S’ that appeared on the issues of the Royal Bank of Scotland from 1967 to 1986—to the full name of the authority or country—such as ‘INDONESIA’, ‘QATAR MONETARY AGENCY’, and ‘BANCO CENTRAL DE BOLIVA’ on the latest issues of the respective countries.

Usually the micro-printing is printed so that it can be read only from one side of the bank note, the printing appearing in reverse when read from the other side. The new $100 notes from the United States of America have addressed this problem by having ‘USA 100’ printed repeatedly on the thread so that it can be read alternatively from the front and the back.

Whilst we often find it difficult to read the micro-printing, further difficulties arise when some countries have the micro-printing done in their own scripts. The notes of Thailand have micro-printing in Thai script, and the latest issue from Oman has an Arab script.

Interestingly, micro-printing can be done on a metal thread, as can be seen in the latest issue of Saudi Arabia. When held to the light the thread appears solid and there is no reason to doubt that the threads are not still made of silver. When laid down, submitted to good light and magnification, the letters SAMA can be seen—for ‘Saudi Arabian Monetary Agency’.

Another development is the ‘contoured’ thread, which has one straight side and one side with a contoured or wavy pattern. The thread is actually the product ofa wider thread cut in two by a computer controlled laser beam, and was first developed by the Bank of England and the U.K. Atomic Energy Authority.

The contoured thread made its first appearance in the £50 note of the Bank of England in 1981, and has subsequently been used in the five hundred kronor note of Sweden that was issued in 1986. An interesting point to note is that because each thread is the result of splitting one thread into two, the wavy side of the security thread can face either to the left or the right of the bank note.

One further development with the security thread is to make it react with ultraviolet light. This feature can be seen on the recent notes of Bolivia, where the security thread glows (or fluoresces) dark blue when placed under ultraviolet light. This feature will probably become more popular as the use of ultraviolet sensitive inks on bank notes is becoming more common.

Modern security threads have usually been black, but bank notes are now appearing with coloured threads. The latest five piso note from the Philippines has a green broken thread, and the commemorative 60 baht note from Thailand has a broken thread that has translucent, blue and red sections.

The Thai note is a particularly good example of illustrating how the many variations of the modern security thread can be combined in one issue. Not only is it a broken thread, but it has two colours, it has micro-printing and the blue sections of the thread fluoresce under ultraviolet light.

The latest development in the use of security threads is the windowed or ‘Stardust’ thread, which was also developed by the Bank of England Note Printing Works. When viewing notes with this feature from the rear, the thread looks like any other metal thread (except that it is wider than usual), but when viewed from the front, the thread looks as if it has been woven through the paper.

The windowed thread first appeared in the £20 Bank of England note when it was modified in 1984 and has subsequently been used in notes from many other countries including Malaysia, Turkey, Sri Lanka, Germany, Nigeria and New Zealand.

The main reason for the development of the windowed thread, was the need for a device that could not be easily photocopied. For this reason the exposed areas of the thread have a lustre that will not be replicated when the note is copied. The 1990 issues of Germany feature a windowed thread that is coated with aluminium and it is not unreasonable to postulate that other windowed threads are coated with the same material.

The lustre on the windowed threads is important as it is impossible to photocopy. This distinctive feature has recently been copied by the West African States who have placed a tape on the front of their notes to the left of the security thread. The tape is clear with sections of a shiny metallic surface at regular intervals, thus inhibiting forgery by photocopying.

The security thread has certainly become a common device in the production of modern bank notes, and as with any good security device, it can be redesigned in many ways to incorporate additional features. The proliferation of these additional features is making it both more difficult for would-be counterfeiters and more interesting for bank note collectors.

Whilst it is possible that the future direction of bank note manufacture lies with plastic, it is probable that only a few authorities will be issuing their notes in plastic in the next ten to twenty years. For this reason, we will still be seeing the security thread in all its manifestations for some time to come—and who knows, we may yet see a security thread in a plastic note.

The final mention in this discussion of security threads must go to the metal thread that wasn’t! During the Nigerian civil war (1967-70) Eastern Nigeria declared itself independent under the name of the Republic of Biafra. Biafra’s first issue of bank notes was in the denominations of five shillings and one pound, and on these notes appeared a string of printed marks designed to look like a ‘Morse code’ thread. Perhaps they did their job—most likely they didn’t—certainly their second issue had neither a real thread nor a `pretend’ one!

Completed in January 2000
© 2000 Peter Symes