What types of security inks are there?
Here's a few....
Biometric inks contain DNA taggants that can be machine read or react to a reading solvent. This allows for verification of a genuie product and each batch of printed documents can contain different biometric properties. These are completely covert but require specialist methods to validate the authenticity.
Bleeding ink prints in black but when exposed to any aqueous solution it will produce a red stain. Authenticity of a document can easily be tested without the use of any special agents. User can just wet a finger and run it across the ink to instantly see the affect of the bleeding ink. This ink is only available for use on dry offset printing.
Coin Reactive Inks
The image printed from this ink is white or transparent. The image is revealed when the edge of a coin is rubbed over the ink. This provides for immediate verification of document authenticity without the use of any special devices. Coin reactive ink cannot be scanned or copied. This ink is available for use with wet or dry offset and flexographic printing.
Erasable ink is used on the background of a document so that when an attempt is made to erase information, the ink rubs off in that area. The ink will also react in the same manner as solvent/chemical reactive inks do, giving you two security features in one. Erasable inks are used on scenic or pantograph backgrounds on checks and certificates. This ink is not recommended when imprinting a document through a laser printer. The high temperatures associated with laser printers will cause problems within the printer when erasable ink is used. Erasable ink is available for wet or dry offset printing.
UV Invisible Fluorescent Inks
UV invisible fluorescent ink is transparent white or colorless and can only be detected under ultraviolet light. If a portion of a secure document is printed with this ink, it can be quickly checked for authenticity by viewing under a UV light. UV invisible fluorescent inks cannot be reproduced on a scanner or copier. This ink is available for wet or dry offset, flexographic and gravure printing.
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 availbale 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/Chemical Reactive Inks.
This type ink reacts to solvents or chemicals, such as bleach, alcohol or acetone. The solvents or chemicals are used by a forger to wash away or alter information on a document. When exposed to the solvents or chemicals, these inks will run, change color, or cause a stain to develop. Tampering is easily detected when chemicals or solvents are used on these inks. Solvent/chemical reactive inks are available for wet or dry offset printing.
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, therfore indicating that a forgery or alteration has taken place. These, again, will be found on checks and if you are to wet your finger with saliva and wipe across the background, you would see the ink smudge.
Magnetic inks are mainly used for serialisation and numbering purposes but is also found in base security inks within banknotes. The ink contains small iron oxide magnetic flakes and allows a number to be machine read. The mosts common application is is check printing and you will find it on the MICR numbering portion of the bottom of a check. This will usually contain the check number, account number and sort code of the bank.
Optically variable ink
OVI's contain minute flakes of metallic film. As the viewing angle is altered the color 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.
Penetrating Ink / Indelible Ink
Penetrating inks contain a penetrating red dye that goes into the fibers of the paper and will show through to the back of the document. Penetrating inks are commonly used on the arabic and MICR numbering of negotiable documents to deter forgers from trying to scrape the number off from the document. If the number is scraped off the red stain remains on the document. Also, if these documents are duplicated, the reproduction could be easily spotted by checking for the appearance of the red stain on the back of the document. Penetrating inks are available for letter press or wet offset printing.
Pen Reactive Ink
A transparent ink that becomes visible with the use of a special felt tip pen. The use of the pen is necessary to verify authenticity but can also be used to void a document that is no longer in use. Pen reactive ink is available for dry offset printing
Photochromic ink can be colored or colorless. When it is exposed to UV light it instantly changes colors. Once the source of UV light is removed it will change back to its original color. The unique properties of photochromic ink cannot be reproduced by a scanner or copier. The authenticity of a document with photochromic ink on it can easily be checked by exposure to sunlight, UV lights or other strong artificial lights. This ink is available in wet or dry offset and flexographic printing.
Secondary Fluorescing Ink
This ink works in the same way as fouoresing ink however it will not glow or show under a UV lamp UNLESS alteration has ocurred. 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 fluores red so that tampering or alteration is obvious.
Visible Infrared Inks
Infrared visible inks are available in readable and disappearing ink. When printed they can look the same but when viewed under infrared light, one will be readable and one will disappear. One example of using these two inks as a security feature would be to print a bar code using both inks. Print the actual readable area of the bar code with the infrared readable ink and other areas of the bar code with the infrared disappearing ink but making it look like a regular bar code. When read by a bar code scanner, only the infrared readable is read by the scanner. If a forger tries to duplicate the bar code as it looks on the printed document, using regular inks, the bar code would be rejected when read by the scanner because the scanner would read the entire bar code. Visible infrared ink is available for wet or dry offset printing.