FDE 101: Mechanical Printing Processes Expert Overview

In creating counterfeit-resistant documents, traditional mechanical printing processes are often used in combination with one another to print secure, genuine documents and are sometimes simulated by modern digital printing processes. An understanding of the mechanical printing processes used in creating documents, therefore, is essential to properly examine documents for their authenticity.

Forensic Document Examination 101: Mechanical Printing Processes

Forensic document examiners are trained in the identification of printing processes for and security features in documents. The examination requires the use of magnification and lighting conditions sufficient to observe fine details in the documents. The process involves comparing the combination of characteristics pointing to the likely printing processes used in the document production, and comparing the known security features of the genuine document specimen to the characteristics of the likely printing processes and security features of the document in question.

If the examiner observes a combination of characteristics of printing processes and security features in the genuine specimen document that conform to those in the questioned document, the examiner is more likely than not to reach an opinion that the questioned document was determined to be genuine.

If, however, the characteristics of the printing processes and security features of the questioned document do not conform to the genuine specimen, an opinion is more likely than not reached that the questioned document is counterfeit. In conducting this type of examination for a counterfeit document, the characteristics of one or more of the following mechanical printing processes are often considered.

Types of Mechanical Printing Processes

All photo examples are copyright of the Council of The European Union, Public Register of Authentic Travel and Identity Documents Online, PRADO.

Offset lithography has been the dominant process used in the printing industry for decades. It involves the use of printing plates but does not involve impact like letterpress. It is a planographic process, meaning the printing happens along a linear plane. In a basic offset system, when printing on only one side of the paper, the paper to be printed upon passes between two cylinders. The cylinder on top, called the blanket cylinder, rolls across the target object (i.e., paper) and transfers an inked impression to the object. The cylinder on the bottom supports the object as it passes through the blanket cylinder.

There are variations of offset printing presses that involve such things as printing on both sides of an object and applying multiple colors, to include abrupt or gradual color shifting. Regardless of the variation, they all use the basic planographic technique. Primary characteristics of offset printing include sharp, crisp edges without embossing the substrate.

Offset is used extensively for printing on:

• packaging
• newspapers
• magazines
• credit cards
• driver licenses
• birth certificates
• passports
• currency

Letterpress is a typographic process that involves the use of a printing plate with a raised surface that is covered with ink. It is primarily used for paper products. Due to the raised printing surface, it is known as “relief” printing. It is also an impact process wherein the printing plate is pressed onto the paper with high pressure that results in an inked image that is transferred to the paper on a flat surface.

Letterpress printing is characterized by two significant features, both of which are due to the high pressure required to transfer the image to the paper.

• The printing plate embosses the paper, and
• Excess ink that cannot fit in the embossed area is squeezed-out around the edges of the printed material resulting in the “halo effect.”

Over time, plate materials have changed from wood to metal to photopolymers, each of which, combined with the hardness or softness of the paper, influence the embossing and halo effect characteristics

Flexography can be thought of as a sub-category of letterpress. It is a typographic process that involves a printing plate with a raised surface covered with ink. Like letterpress, most printing plates are currently made from photo-polymeric materials and use impact to transfer the image to the object’s surface

Flexography differs from letterpress significantly, however, in that flexographic printing happens on the cylindrical surface of a rotary press. In the flexographic printing system, the surface on which the printing is taking place can be paper, polyethylene, other plastic-like substances, or various types of foils. Flexographic printing is characterized by sharper line definition than letterpress. It also produces a halo effect, but it may not produce embossing.

Flexography has been used to print on:

• government identification cards
• foil
• plastic film
• corrugated board
• paper
• paperboard
• cellophane
• fabric

Intaglio is a printing process by which the image to be printed is recessed into a printing plate. The recessed area is filled with ink and brought into contact with the object surface under high pressure. The ink is thereby transferred from the plate to the substrate.

Characteristics of intaglio printing include a raised surface and a “feathering” or “bleeding” effect at the edges of the printed material.

Intaglio printing is used on:

• currency
• passports
• birth certificates
• automobile titles

Rotogravure is related to intaglio in that it is a recessed image printing process. It involves printing on the cylindrical surface of a rotary press, however, rather than a flat surface. Like offset, rotogravure is used for many types of publications; like flexography, it is used for printing on packaging.

Interestingly, the small trademark image on M&M candies is printed by rotogravure. Everything printed by rotogravure is composed of minute cells, which results in the salient characteristic cell pattern of the rotogravure process.

Screen-process printing involves forcing ink through a mesh material (normally woven synthetic material or steel) that is attached to a frame. Masking material is used to selectively block-out areas of the screen to form the image to be printed. This process transfers much more ink to the object surface than the other process.

Screen printing is used for a variety of purposes, which include posters, art prints, textiles, label printing, printing on bottles, and printing odd shapes such as plastic illuminated signs.

Questioned Document Examinations

Questioned document examination is a discipline within forensic science that pertains to documents with disputed authenticity or origin. A questioned document investigation is used to ascertain the authenticity (or lack thereof) of a document or other item when it comes into question. The examination of known to questioned documents provides analytical results regarding the similarities or differences between the samples using a variety of scientific principles and methods.

To discuss your case with an expert, call us at 800.813.6736 or submit an inquiry.

Source

Council of the European Union, Public Register of Authentic Travel and Identity Documents Online, PRADO, “Glossary, Technical Terms Related to Security Features and to Security Documents in General.”  (Brussels, Belgium: European Union, 2022) https://www.consilium.europa.eu/prado/en/prado-glossary/prado-glossary.pdf (accessed October 24, 2022).

Featured Expert

Gregory Dalzell

Forensic Document Examiner

Gregory Dalzell is a Forensic Document Examiner with 27 years of professional experience in government agency work, with the last 13 years spent serving in the U.S. Secret Service as a Supervisory… read more.