It’s something that often passes by our hands, often faster than we would wish. Today, in The Chemistry of Things, we speak about Euro notes!
Let’s start with the paper.The paper used to make the notes must be particularly tough, since they will be bent, stretched, handled, counted on machines, arranged in the wallet, taken from the pockets … thousands of times during its life!
Paper is made of cellulose, a polymer which is a structural component of plants cell walls. The paper for common use (obtained from the cellulose of various trees) is not tough enough to use on notes.
The paper of Euro banknotes is also 100% cellulose, but in the form of cotton fibers (the same fibers used to manufacture cotton fabrics) which give the notes not only the strength, but also that such characteristic feel.
Ink is not less important than the paper. In fact, the chemistry of banknotes ink is very demanding. Besides being highly stable (no one wants to have their fingers stained after handling a note!), they also have features that allow the printing of security features: Relief printing, two-colour printing, which makes the colour change with the angle, microscopic printing.
One of the security features of Euro banknotes in which chemistry is absolutely brilliant is the photoluminescence effect. What does this mean? If we take a note and put under an ultraviolet light, some printed details gain colour and shine in red, green and blue.
The photoluminescence is indeed a well-known phenomenon in chemistry, since some substances have the ability to absorb light radiation and then send it back! We’ll give you an example: If you like crime shows on TV, you’ve have certainly seen detectives detect bloodstains using a luminescent compound called luminol.
On euro banknotes, this effect is due to a chemical called … europium! Europium is a metal whose ions absorb ultraviolet light and release it in the area of the red, green or blue, depending on the atoms to which they are attached to. We have to agree that it is a very suitable chemical for use in Euro banknotes!
And so we have the secrets of chemistry flowing in our hands … every day!
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