Glossary | Trelleborg Printing Solutions

Trelleborg offset, flexo and digital printing glossary

List of common vocabulary and taxonomy used in offset, flexo and digital printing. Learn more about compressibility, paper feeding, printing blankets values, inks and printed surfaces

Trelleborg Printing glossary

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Four Colors printing on the front side, no printing on the backside of a printing job

Four colors on the front side, four colors printing on the backside of a printing job

Four Colors printing on the front side, one color printing on the backside of a printing job


Back Up
Alignment of an image on the front side with the image on the backside of a sheet

The department in charge of cutting, folding, collating, drilling and finishing on printing projects

Creating a finished book using smyth sewing, gluing or stapling to let edges of pages adhere

Composite material made of some fabric and rubber compound layers secured onto a cylinder transferring ink from the plate to the paper

Blanket surfaces 
The offset blanket surface structure, profile, and hardness are extremely important and contribute significantly to the printing performance of an offset blanket. Additionally, surface imperfections will certainly cause printing problems; therefore, production standards are set to guarantee the highest quality of printing surface.   
It is not an easy task to develop a suitable rubber compound for the printing surface of an offset blanket utilized for high quality offset printing. The difficulty is due to the conflicting chemical and mechanical requirements which can be found during the printing operation.   
The blanket surface must exhibit a "dual" personality. The surface rubber compound must have the capacity to take the maximum amount of ink possible from the printing plate without distorting the image and transfer it almost half way around the cylinder to the printing stock. This precise operation must be done at very high circumferential speeds.   
The tack of the printing surface must remain low in order to ensure a minimum build-up of paper dust, dirt, and ink.

The area over the trim line used to conceal cutting variances for artwork that extends to the edge of the page

When piled printed sheets stick together, sometimes damaging print jobs. It is due to lack of anti-offset powder or excess of ink

Book Paper
Paper used for book printing. It can be matt coated, gloss coated or uncoated

When printed image and sheet positioning are not well aligned during the printing process

A paper finished with a mineral coat

Cold colour
Any color that is toward the blue side of the color spectrum

Colour bars
Checking bars of printed colour on a useless part of paper to test ink density

Colour gamut
The complete span of colours that can be reproduced by a system

Colour sequence
The sequence of colors on the printing press cylinders

Colour shift
Non uniform colors on printing jobs, due for instance to wrong ink densities, color register, dot gain

Compressibility and Reboundability 
In a compressible offset printing blanket, compressibility is the single most important factor influencing dynamic performance on press and print quality. With reference to offset blankets, compressibility is defined as the volume reduction capacity of a substrate under load. Vulcan compressible blankets have in their carcass a specially designed compressible layer which allows the blanket structure to be compressed in the printing nip without creating "bulges" on either side of the nip.

Offset blanket compressibility is a very important factor in the printing process. Having the proper range of compressibility will prevent excessive printing pressures and should help to lengthen the lifetime of the press, blankets, and plates. Furthermore, the compressibility factor also allows the blanket to recover sufficiently and quickly after smashes without resulting in distorted print  quality. And, last but not least, it considerably shortens make-ready times.   
In addition to blanket compressibility, there is the factor of reboundability or resilience. This characteristic should not be confused with compressibility as it is quite different and can not be measured with the same instruments. In fact, reboundability or resilience is measured with a Rebound Tester and/or Resiliometer. Compressibility, on the other hand, is tested with a Cady-Fag or laboratory equipment like an Instron Tester.

The degree of tonal separation or gradation in the range from black to white

How much a substrate is covered during a printing process

A shade of blue used in four-color process printing. The C in CMYK

The process where rollers cover non-printing plate areas with a oil repellant solution so that they repel ink during an offset printing process

The opposite of emboss, where the image is raised above the paper surface

Optical device that controls the density of ink or color

Die Cutting
Paper cutting thanks to steel rules using a wooden die

The littlest part of a halftone

Dot gain
Dot gain is the difference between the original intended dot and the one reproduced.  Dot gain is caused when an image is transferred from one source to another. Consequently this includes the transfer of ink from the plate to the blanket and then again from the blanket to the substrate.  Other things that influence dot gain include the absorption rate of the substrate, inks and press settings.   

Dot gain is planned for throughout the print process and can be regulated in the pre press area. Acceptable degrees of dot gain vary depending on the substrate.

The ability of a blanket to last for a long time without significant deterioration is dependent on several factors. It is dependent on the substrate being run, the balance of chemistry, the craftsmanship used and the blanket itself. Each one of these factors impacts the life of the blanket. 

  • Substrates – some substrates are tougher on blankets then others. Plastic, paper with lots of Calcium, coarse stocks or unusual finishes all add to the demise of blankets.
  • Chemistry – Well balanced chemistry impacts blankets more than people think. Having the wrong chemistry allows ink build up causing problems such as wear, window framing as well as a slew of other printing problems related to both ink and blanket. Then there is the question of intermixing applications such as UV, conventional and hybrid printing. This requires testing before recommending a blanket.   
  • Craftsmanship – There are two sides to the usage of every product. On one side, the manufacturer has to make it properly and on the other side it has to be used properly. No matter how good the blanket is, it won’t perform to its potential if it is not packed properly, torqued properly or is not maintained during the run.    
  • Blanket – Not all blankets perform the same. Manufacturers make a variety of blankets for a reason. Blankets are made for different substances, different applications, to fight pricing or different types of presses. The trick is to find the best blanket for the press and application.     

Each shop has its own characteristics and can only compare blankets in its own environment. There are shops that can run blankets for millions of impressions while others are changing them out constantly. It is difficult to compare two shops. Every shop looks for different qualities in a blanket, to some it’s durability to others it’s printability and yet others look for release.

Edge marking 
is caused by paper fiber left on the blanket causing a buildup on the surface. The buildup cuts into the surface of the blanket. Edge marking happens on the blanket surface, at the edge of the sheet or web and is influenced by a couple of different factors; the surface rubber of the blanket and the husbandry of the pressroom.

Blanket stretch can be defined as "the amount of elongation under a given load". The elongation measurement is determined by the design and quality of the textile fabrics used in the manufacturing process. In Vulcan blankets, the fabrics utilized are woven from only high quality cotton yarns and this fact contributes to their resilience, stretch- resistance and overall strength flexibility.   
The raw cotton used in the fabrics (textiles) is spun on state-of-the-art machinery, into yarns which are then woven into specially designed fabrics. After weaving operations are complete, the rolls of fabrics are inspected for defects like small knots, ruptures or small holes. Some fabrics, depending on their function or position in the blanket design also go through a stretching process which helps to reduce their elongation factor to an extremely low level. In fact, a blanket with very low elongation will be easier to tension to the proper load during mounting. Also fewer retensioning operations will be necessary and the blanket will lose less thickness during and after installation.   
Raising of the paper thanks to metal dies, heat and pressure so that an image is raised too

A positive feed blanket, tends to “give more paper”, the tension of the paper after the printing unit will decrease compared to the in-feed unit. This means that the web will tend to flutter, due to its tension loss.    

With a negative/neutral feeding blanket the tension of the paper will be higher than the in-feed. This means that the web will get to the next printing unit properly tight.   
Example of blanket with positive feeding:   
Reel stand: 200 N  In-feed: 220 N Load cell: 170 N or < than in-feed unit
Example of blanket with negative feeding:   
Reel stand: 200 N  In-feed: 220 N Load cell: 220 N or > than in-feed unit
With a blanket with positive feeding, the web will tend to follow the leading blanket cylinder, resulting in bad paper release.

Fifth Color
The color on the printing press exceeding standard cyan, magenta, yellow and black used in 4 color process printing. It is usually a custom or Pantone color

Appearance of the paper surface

A printing process that stamps a metal finishing to paper

Foil Embossing
The union of foil printing process with embossing, to obtain a raised and metallic printed area

Gauge loss
An offset blanket will lose some of its thickness during mounting as a result of the initial tension applied during the mounting process as well as during initial printing operations.

A new blanket, once tensioned on the cylinder, loses gauge because the textile layers are stretched during installation. In the early days of offset printing blankets, the textile fabrics utilized in blankets had a high elongation factor e.g. 2-3%. Current press performance requirements call for low(er) stretch blankets which "settle" very quickly on the cylinder with the lowest loss in thickness possible.   

A 1,95 mm thick printing blanket, once tensioned on the blanket cylinder, may lose 1-2% in thickness, with an additional loss of another 1% during the press run (see illustration 10). The lower the gauge loss, the more stable a blanket is on the cylinder and, consequently, fewer blanket retensioning operations during printing will be necessary.   
A printing issue due to a faint image appering on one side of a printed sheet, because of interaction between drying ink vapors and paper/dry ink

The direction of paper fibers on a sheet. A fold should be parallel to grain

A way of printing where concave areas of metal cylinders hold ink


Creating an image that seems continuous using small dots of different sizes and different in number per area

The hardness of offset blankets is normally measured on the Shore A scale. Many printers are aware that there are on the market so-called soft, semi-hard and hard blankets. When a printer requests a "hard" blanket from his supplier, does that mean the printer wants a blanket that is hard or a blanket with lower compressibility?   

Even today there still exists some confusion regarding Shore hardness and how to correctly measure this characteristic. As mentioned before, an offset printing blanket can be divided into two components: the printing surface (face) and the carcass (normally 3 or 4 ply configuration). The printing surface is 100% rubber whereas the carcass is a composite structure of textile fabrics and rubber or polyurethane cements between the plies. Taken separately, these two parts have different hardnesses. A portable Shore A durometer, if used on the printing surface of the blanket, will give a certain reading until its needle penetrates the printing surface and encounters resistance from the blanket carcass. Therefore, when the hardness of a printing blanket is measured, it will be the top fabric layer that substantially alters the durometer reading.

Bear in mind that Shore A durometer measurements have not been designed to accurately measure the hardness of a fabric and rubber composite.
Durometer testing is normally associated with the measurement of the hardness of a small piece of sheet rubber containing no fabric.   
Therefore the average load value gives the printer a much better understanding of the hardness of the blanket.

Image area
The part of plate containing the image to be transferred

is defined as the amount of compression of an offset printing blanket when squeezed in a printing nip. It is expressed in hundredths of a millimeter or thousands of an inch. Indentation should not be confused with other terms such as height over bearer, pressure or impression   
Due to the blanket design or intended use, it may require either a high or a low indentation value to achieve proper print characteristics.   
Low indentation blankets such as conventional blankets must be packed with extreme accuracy, especially after smashes. The minimum indentation required for successful performance of. an offset blanket should not be less than 0,08 mm (.003"). Printers should always bear in mind that although every compressible offset blanket has a proper indentation value, field surveys show a preference for blankets having an indentation range of 0,10-0,15 mm (.004"-.006").

Ink dry back
A lightening or a loss in colour density after drying on paper

Perfectly alignement of piled printed sheets using vibrations, to cut or bind them precisely

Reducing spaces between letters to gain space on a line

Protect paper and make it resistant covering it with thin and transparent plastic sheets on both sides

The use of curved and inked surfaces to print images, such as in offset printing

A primary color similar to red, with some blue, used in the four colour printing presses and in CMYK printing processes

Metallic Ink
A type of ink that contains metallic powder or pigments to give a metallic finishing to the printing job

Anomalous angulation of halftones

A printing issue happening when ink is not well absorbed or is spot on the printing surface

Paper used to print newspaper, low-cost, unbleached and light weight

Offset printing
Printing process where the image is transferred from a plate to a printing cylinder covered by a rubber printing blanket and then impressed on the printed surface

Creeping or the movement of packing along the cylinder surface can be caused if the cylinder surface speeds are not synchronized or if the blankets are improperly tensioned. Even self-adhesive foils installed on blanket cylinders will creep if there is a speed differential between the blanket and impression cylinders!

Typographic measure corresponding to 1/6 of an inch

When during prinitng paper particles are pulled by ink and leave spots on the printing job

Pantone Color Matching System

Typographic measure corresponding to 1/72 of an inch. 12 points are a pica, 72 points are an inch


is the ability of paper to come off or be released from the blanket, during the printing process. It is one of the most over used terms in printing. As an industry we call for better release any time we see an elongated dot but there are many factors that influence this phenomenon. Presses - In sheetfed, registration devises, including grippers, may be dirty or require calibrating. In web formats forms may be laid out improperly placing all of the coverage on side of a form and nothing on the other side causing an unnatural pull from side to side. Machine layout also impacts the way stock pulls off of a blanket. Some web presses have staggered units with the upper unit being slightly forward of the bottom unit. This causes additional concerns and plays an even larger role in how forms are laid out.   
-Ink – Ink impacts release in a couple of different ways. Tack and viscosity have a direct influence on release, the higher the tack/viscosity the worse the release. However, too low a tack produces a slew of other printing problems not to mention ink spraying throughout as it’s milled through the press rollers.   
-Surface tension – Some blankets have a better release than others. Some are constructed in layers allowing for better release and buffed a little more coarse allowing the paper to leave the blanket easier.   
-Blanket washes – Another factor in release are different types of chemistry used as a blanket wash. There are many different types of washes, all designed for different applications. Some rejuvenate blankets to their velvety soft surface, some use harsh chemicals designed to cut through calcium and ink almost melting the blanket surface.

Perfect alignment of more printed images

Register marks
Symbols on a printing job that assure perfect register

Red, green and blue. These colours are mixed to obtain all other colours. To be printed, the RGB file has to be transformed in CMYK

Rich black
Reproducing black using more colours to create a deeper black

Printing dots in a smaller size, reducing colour intensity

One printed sheet whit more pages. Folded, it will result in the exact sequence of pages of the printed job

is the process of where a blanket falls to a new lower level than when brand new.  This could be a small section, the lead edge or the entire blanket.     
A small section of the blanket sinking could be a manufacturing defect or could be a situation where the sinking is actually a smash but the perpetrator is not found. In some cases there are ways to tell the difference using a high powered scope.  A smash will have sharp edges around it where as sinking may have soft edges leading into the rest of the blanket.

The lead edge of a blanket may not be able to withstand the sharp edge of the cylinder drop off and collapse right before the drop off of the cylinder. Printing in that area is now very difficult unless the cylinder is built up to make up for the crashed fibers in the blanket.  Lead edge sinking can also come from improper torque techniques.  Once a blanket is over torqued  the layers in the center are crushed and thus not able to perform as intended.   
New blankets have a settling property about them. Once placed on the cylinder the fibers settle and air is defused from the material itself causing the blanket to settle one or two thousands. This is not considered sinking. The blanket is merely settling. Once that happens and the blanket gets re- torqued it should run effortlessly with any further assistance.  However there are blankets that are poorly manufactured where they sink every few thousand impressions and cannot hold gage .  These are blankets that are poorly constructed in the planning stage or are defective.

Smash Resistance 
Edge marking is caused by paper fiber left on the blanket causing a buildup on the surface. The buildup cuts into the surface of the blanket. Edge marking happens on the blanket surface, at the edge of the sheet or web and is influenced by a couple of different factors; the surface rubber of the blanket and the husbandry of the pressroom.

Blanket surfaces can and do make a difference in edge cutting. Some blankets have a tough surface and resist edge cutting while others have a softer surface and cutter easier. Chemical compounds that formulate the surface rubber make a difference in edge cutting but another big factor is the stock itself. All blankets cut at some point or another but the difference is frequency.

Soy Inks
Inks that contain soy oil to be more environmetal friendly and reduce the use of petroleum oils

a blanket on the cylinder is a very crucial operation and it must be done precisely in order to:   
1)   guarantee blanket conformance to the blanket cylinder surface, particularly at the gap area.   
2)    prevent the shifting of underpackings.   
3)    avoid blanket movement, due to insufficient tension, during printing operations.   
The exact amount of tensioning will depend on the press type and design of the blanket lock-up system. It is extremely difficult, if not impossible, for the blanket manufacturer to provide precise tensioning details and recommendations. EACH PRESS TYPE can require different amounts of tensioning due to:   
♦    type and design of the blanket lock-up system.   
♦   amount of tension transmitted to the blanket from the lock-up system. It is very important to understand that the printer applies tension to the lock-up system which, in turn, applies tension to the blanket. The lock-up system, depending on its mechanical (gear) ratios, can transmit either a fraction of or a multiple of the initial tension to the blanket.   
♦    diameter of the blanket cylinder.   
♦    type of underpacking used.   
♦    cleanliness, lubrication and wear of the blanket cylinder lock-up system.   
♦    variations in the stretch properties from one blanket type to another.   
♦    variations in mounting techniques from operator to operator.   
Overtensioning can cause high gauge loss, cracking at the gap and bar pull-off. Insufficient tension, on the other hand, can create problems like doubling, slurring, blanket movement, registration shifts and plate wear. Of the two practices, overtensioning is by far the more prevalent cause of problems.   
(blanket) In the printing field, the required thickness of a blanket is normally indicated either by use of the terms 4 ply and 3 ply or by indication of a thickness such as 1,95 and 1,70 mm (.077" and .067") with appropriate tolerances. Both these indications stand for nominal values! A 4 ply blanket normally has a 4 ply structure (4 textile layers in the blanket carcass) whereas thickness reference will always be in the range of ± 1,95 mm (± .077") due to the nature of the blanket manufacturing process.   
In some cases when printers reference a ± 1,95 mm thick blanket, they may be referring to a 4 ply blanket which, instead, has a 3 ply structured carcass. Normally, a true 4 ply structured blanket will have higher stability on the blanket cylinder during the printing process as compared to a 3 ply structured 1,95 mm thick blanket. Today's trend, in the case of 4 ply thick blankets, appears going more towards the range of 1,94 - 1,98 mm (.0765" - .078") rather than 1,90 - 1,94 mm (.075"-.0765").   
European offset printing machinery requires for the greater part ± 1,95 mm - 4 ply blankets, with a very limited number of presses using 3 ply - 1,70 mm thick material. The situation with USA built machinery is just the reverse.   
It's obvious that a large thickness variation in a single blanket will influence print quality. To obtain the best printing conditions possible, the blanket cylinder should be in impeccable condition, the packing material used should be hard with the lowest possible variation in gauge and instructions given by the press manufacturer should be followed as accurately as possible.   
According to international standards, a total of 0,02 mm (.0012") variation in thickness within a one square meter compressible blanket is acceptable

Halftone made of dots of the same size

Avoiding of white visible spaces using overlapping of colors, used most of all where there are color registration variations

Trim marks
Marks on a printing job to know where it has to be cut

UV Coating
A liquid coating cured with UV light to give a glossy and long lasting coating to the printing job

A protective and glossy layer for printed jobs added as a finishing

Volatile organic compounds. Petroleum component of some inks and varnishes that easily evaporate

Warm color
A color where red tons are prevalent

Embossed or printed mark visible when paper is looked against the light

Web press
Printing machines fed by large and long rolls of continuous paper, the web


A primary colour, part of the CMYK model


Sources: internal information, Internet resources