Security printing

Security printing is the field of the printing industry that deals with the printing of items such as banknotes, passports, stock certificates, postage stamps and identity cards. The main goal of security printing is to prevent forgery or counterfeiting.

A number of technical methods are used in the security printing industry.

Special paper

Most banknotes are made of heavy paper, almost always from cotton fibres for strength and durability, in some cases linen or speciality coloured or forensic fibres are added to give the paper added individuality and protect against counterfeiting. Some countries including Romania, Mexico and Australia produce banknotes made from polymer, in order to improve wear and tear, and permit the inclusion of a small transparent window a few millimeters in size as a security feature that is very difficult to reproduce using common counterfeiting techniques.

Watermarks

A watermark is a recognizable image or pattern in paper that appears lighter or darker than surrounding paper when viewed with a light from behind the paper, due to paper density variations. A watermark is made by impressing a water coated metal stamp or dandy roll onto the paper during manufacturing. Watermarks were first introduced in Bologna, Italy in 1282; as well as their use in security printing, they have also been used by papermakers to identify their product.

Intaglio printing

Intaglio is a printing technique in which the image is incised into a surface. Normally, copper or zinc plates are used, and the incisions are created by etching or engraving the image, but one may also use mezzotint. In printing, the surface is covered in ink, and then rubbed vigorously with tarlatan cloth or newspaper to remove the ink from the surface, leaving it in the incisions. A damp piece of paper is placed on top, and the plate and paper are run through a printing press that, through pressure, transfers the ink to the paper.

The very sharp printing obtained from the intaglio process is hard to imitate by other means.

Geometric lathe work

A guilloché is an ornamental pattern formed of two or more curved bands that interlace to repeat a circular design. They are made with a geometric lathe.

Microprinting

This involves the use of extremely small text, and is most often used on currency and bank checks. The text is generally small enough to be undiscernable to the naked eye. Checks, for example, use microprint as the signature line.

Holograms

A hologram may be embedded either via holographic paper, or onto the laminate of a card itself.

Security threads

There are two kinds of security threads. One is a thin aluminum coated and partly demetalized Polyester film thread with Micro printing which is embedded in the security paper as banknote or passport paper.

The other kind of security thread is the single or multicolor sewing thread made from cotton or synthetic fibers, mostly UV fluorescent, for the bookbinding of passport booklets.

Magnetic ink

Because of the difficulties in forging magnetic ink characters, and the speed with which they can be read by computer systems, magnetic ink character recognition is used extensively in banking, primarily for cheques.

Serial numbers

Serial numbers are not difficult to forge, but make legitimate documents easier to track and audit.

Anti-copying marks

In the late twentieth century advances in computer and photocopy technology made it possible for people without sophisticated training to easily copy currency. In an attempt to prevent this, banks have sought to add filtering features to the software and hardware available to the public that senses features of currency, and then locks out the reproduction of any material with these marks. One known example of such a system is the EURion constellation.

Copy-evident paper

Many secure documents have the feature which causes a photocopy of the document to appear obviously different from the original. For example, when photocopied, most checks will display the word "VOID" (or the equivalent in another language) on the copy, even though it is absent from the original.

Fluorescent dyes

Many banknotes incorporate dyes which fluoresce under ultraviolet light. These show up as words, patterns or pictures under UV. This feature is also incorporated into other documents - eg Northern Ireland NHS prescriptions show a picture of local '8th wonder' the Giant's Causeway in UV light.

Registration of features on both sides

Banknotes are typically printed with fine alignment between the printing on each side of the note. This allows the note to be examined for this feature, and provides opportunities to unambiguously align other features of the note to the printing. Again, this is difficult to imitate accurately enough in most print shops.

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