Security Inks

What types of security inks are there?

Security inks are available to protect printed materials in different guises.



Invisible Ink

One of the most widely used inks is invisible ultra violet and will be revealed when the print is placed under a black lamp (or UV light source). The ink is invisible to the eye (covert) under normal lighting conditions. When passed under a uv lamp the ink glows and is used predominantly for cheque printing and document protection in the UK. It is relatively cheap and is available in many colours. The ink must be applied to a UV dull substrate otherwise it will not be visible.

Thermochromic Ink

Thermochromic inks are sensitive to temperature changes and will appear or disappear at different temperature ranges. If you were to apply a finger and thumb to a 15 °C dark blue printed thermo spot the ink would disappear to nothing and as soon as you removed the heat source the ink would re-appear again. Inks come in various temperature sensitivities and common temperatures available are 15°C, 31°C and 45°C. An important consideration would be where the ink is to be located. In hotter climates you may well have to go for a higher temperature as the ink could be invisible from the ambient temperature itself. Some are available as a permanent change. e.g. when it has reached a temperature the ink colour does not reverse - this may be used on labelling for food product packaging where you could see if an item has thawed out and would be dangerous to re-freeze again.

Solvent Sensitive Ink (reactive)

As the name states, would present a visible indicator that the ink has been attacked by a solvent (usually attempt to remove variably printed information such as a cheque). You will mainly find this being used on a printed watermark or fine guilloche artwork design. Once a solvent has been applied the ink will change colour to show that alteration has been attempted.

Optically variable ink

OVI's contain minute flakes of metallic film. As the viewing angle is altered the colour morphs from one to another. This needs to be printed with a fairly heavy weight to get the best results. The inks are very expensive and are usually printed in small areas. Such examples would be in currency printing and visa's. The most common colour changes are brown to green (and vice versa) as well as red to purple. You will also notice that the ink feels almost embossed on the substrate which is due to the amount of ink required to get the required effect.

Magnetic Ink

Magnetic inks are mainly used for serialisation and numbering purposes. The ink contains small magnetic flakes and allows a number to be machine read. The most common application is is cheque printing and you will find it on the MICR numbering portion of the bottom of a cheque. This will usually contain the cheque number, account number and sort code of the bank.

Biometric Ink

Biometric inks contain DNA taggants that can be machine read or react to a reading solvent. This allows for verification of a genuine product and each batch of printed documents can contain different biometric properties. These are completely covert but require specialist methods to validate the authenticity.

Fugitive Ink (water based)

Fugitive ink works similarly to solvent sensitive ink in the fact that any form of alteration (with water or an aqueous solution) will make the ink run so that the printed pattern or area becomes smudged, therefore indicating that a forgery or alteration has taken place. These, again, will be found on cheques and if you are to wet your finger with saliva and wipe across the background, you would see the ink smudge.

Secondary Fluorescing Ink

This ink works in the same way as fluorescing ink however it will not glow or show under a UV lamp UNLESS alteration has occurred. This is a secondary measure to protect against tampering and alteration. Quite often you will have an invisible ink that fluoresces green under a UV lamp and a secondary ink that will fluoresce red so that tampering or alteration is obvious.

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Update: 13/12/2013 Spelling and terms