How to subdue the Reflex Blue Blues

Reflex Blue (a.k.a. Red Shade Alkali Blue, Pigment Blue 61, Reflex Blue R 54/R 56) is one of the most commonly used spot colors - especially for corporate colors - and it is one of the most problematic inks to use on press.

Reflex Blue suffers from excessive marking, low scuff resistance, poor lightfastness and poor, very slow, drying qualities. It also has a bronzed look that causes it to shift color, from Blue to Purple when viewed at different angles.

And when mixed as part of another blue spot color, Reflex Blue effectively contaminates that ink color with its poor performance characteristics.

Reflex Blue Blues - slow drying

Printing inks are made primarily with resins, varnish, linseed oil, soybean oil, or a heavy petroleum distillate as the solvent (called the vehicle) combined with organic pigments. The resins and varnish control the tack and gloss of the ink while the solvents control press stability and fluidity. Drying oils control surface strength, drying time, and set, while the pigment acts as the coloring agent.

Although each ink pigment is unique, most have fairly uniform shapes and surface areas. Reflex Blue pigment on the other hand has jagged, irregular surfaces and shapes. To blend Reflex Blue ink, ink manufacturers must add surface active agents to the mix that allow proper wetting of the pigment. As a result, the ink retains a higher level of moisture than other ink formulations and therefore takes longer to dry.

Offset inks are generally designed to dry by two methods: absorption into the paper and evaporation from the surface. As the ink dries, the small, uniform color pigments settle close together and leave a flat ink film surface. However, when Reflex Blue pigments set they have a rough ink film surface. Although the ink may feel dry to the touch, just a light rub will break the surface and expose the wet pigment underneath. This results in unsightly scuff marks and color transfer (set-off) to surfaces that come into contact with it.

Reflex Blue Blues - color shift/burn out

Reflex blue  color-shift or "burnout" can occur when the printed ink film is over-coated with aqueous, or UV coating.  This affect results from a chemical reaction due to pH incompatibilities between the alkaline aqueous coating and certain alkaline sensitive ink pigments like Reflex Blue. The chemical reaction basically changes the way the color pigments reflect light. Individual press sheets pulled during the press run or top sheets in the pile are rarely as affected as the sheets within in the press loads. This indicates that heat and oxygen deprivation are contributing factors in accentuating and accelerating, the color-shift effect. Unfortunately the color-shift may not be apparent immediately off press and may take 24 hours or longer to be noticeable.

Tips for subduing the Reflex Blue Blues

1 Don't use it. If that's too drastic then:
If you are a printer, speak to your ink vendor. Most will stock an "imitation" Reflex Blue substitute. The most common is a Carbazole Violet & Phthalo Blue mix. Note that the imitation Reflex Blue may have a slightly different hue than the actual Reflex Blue so do a drawdown of the ink and get customer approval.

If you are a print buyer/specifier, speak to your print supplier about selecting an "imitation" Reflex Blue substitute. Get drawdowns of the ink and, once satisfied with the hue, document the ink manufacturer, ink series and name so that the same ink can be used for all your Reflex Blue needs.

2 Print the job using UV inks since they dry immediately.

3 Print small lifts. Shorter stacks of paper at the press deliver facilitate faster drying by allowing more air to circulate between sheets enabling gasses to escape. Shorter stacks will add a small amount of extra run time on press. Wind the printed loads as soon as possible to reduce unnecessary exposure to high heat builds captive in the pile.

4 If the shop runs a five day production schedule then print on Friday to allow the sheets to dry over the weekend before printing the second side or sending the presswork to the finishing/binding processes.

5 Consult with the printer/ink vendor to determine whether reformulating the Reflex Blue ink by adding drying agents. Note that doing so may increase cost and/or compromise the inks on press performance in other ways - e.g. it may adversely affect te quality of screen tint areas.

6 Apply a varnish, aqueous or UV coating to help seal the ink and eliminate scuffing, fingerprinting, and bronzing of larger ink areas. Use a low-amine or heat-resistant aqueous coating with as low a pH as possible (less alkaline). Inform your ink supplier of the need for alkali or fade resistant inks compatible with aqueous or UV coating and also consult with you coatings supplier and are assured of these pigments’ compatibility with their product. Confirm that the coating to be applied has been thoroughly tested prior to running the job.

7 Beware that UV coating, in particular, does not coat well over Reflex Blue and will sometimes fade or change the ink color. Pre-test Reflex Blue, especially tint solids and screens, by wet-trapping half the image with selected coating and then expose both samples to a high-heat source such as a heated saddle dryer. On-press testing is usually required to simulate actual production with ink and fountain solution. For side-by-side comparison, cut the coater blanket packing half-way through the printed ink film to be tested. Then expose the coated and uncoated print samples to a heated dryer saddle immediately off press. Burnout and color-shift will usually occur during heat application. If time permits, wait 24 hours, then reapply heat, and again compare the color integrity of the test samples. Test, test, test.

Other alkali sensitive pigments that can have similar issues to Reflex Blue include:
• Rhodamine Red - (Y.S. Rhodamine Red)
• Purple - (B.S. Rhodamine Red)• Warm Red - (Red Lake C)
• Violet - (Methyl Violet)
• 072 Blue
• Rubine Red - (Lithol Rubine)
• Fluorescent inks

Pantone color shifting - the problem with coatings

I think that most of us have been hit with an unpleasant surprise when a Pantone ink color shifts after being UV or aqueous coated. As one example, Reflex Blue (arguably the most difficult color in printing) prints as dark blue but will dry with a reddish sheen that will not dry properly. To try and make it dry faster the printer might run it through the press a second time to apply a coating, either UV or Aqueous, to seal the ink. This causes an immediate color shift which will continue to shift over the course of a few days.

The colors in the table below, as well as any spot color recipes that use them in the formula, will shift color (a.k.a. alkalinity burn) when subjected to the alkalinity of a aqueous or UV coating.
In order to avoid the costs involved with reprinting a spoiled job, when mixing and/or specifying PMS colors it's critical to inform your ink vendor that you will be aqueous or UV coating the job.

Special thanks to Bob Peterson of Superior Ink for his contribution to this post.

On-press stability and consistency

A printing press is a device for laying down a film of ink onto a substrate. Each component on each press unit, from ink ductor rollers to ink train oscillation moves or rotates with a repetitive frequency and this shows up as solid ink density variation. When the natural solid ink density variations through the press run are graphed, the result is sometimes referred to as the "heartbeat" of the press because of its resemblance to the rhythm of a human heartbeat.
The heartbeat of a press - the solid ink density variations measured over through the press run. Each of the 3 sections contains 100 press sheets from the beginning, middle, and end of the press run. Each "heartbeat" in each section is the solid ink density variation between 10 sheets. So, each of the three sections contains the SID measurements of 100 sheets.
The human heartbeat.
Every press design has its own "heartbeat" profile that represents its normal condition. What one looks for are abnormalities in the heartbeat profile itself as well as in comparison between different press units. Plotting the heartbeat of the press, just as it does with humans, can help diagnose problems in the system that may need correcting.

Solid ink densities varying naturally through the press run cause dot gains - tone reproduction - to also vary which in turn causes color shifts in the presswork. Below, courtesy of data provided by Alwan Print Standardizer, is a movie showing dot gain variation through the press run.
Click on the expand icon (the four arrows) to enlarge the video for greater clarity. Then click on the play arrow.
It's fair to say that a printing press in proper working condition is stable - but not consistent. And that fact applies equally to the presswork itself. Therefore, since variation is an integral characteristic of the printing process, the important thing is to establish, and communicate between buyer and print provider, what the target for presswork color should be, how it will be measured, and what range of variation is acceptable based on the needs of the specific job at hand.

Printing Standards and Specifications

Printing standards and their associated specifications bring an independent, authoritative, and concrete basis for file preparation, proofing, presswork, and output evaluation. They reduce proofing cycles and enable faster approval processes. They also help synchronize expectations between print buyer and print provider.

I'll begin with a few definitions.

A Standard according to the International Organization for Standardization (ISO) defines a standard as:
"A document established by consensus and approved by a recognized body that provides for common and repeated use, rules, guidelines or characteristics for activities or their results, aimed at the achievement of the optimum degree of order in a given context."

A Specification is not a standard. Rather, it is a detailed description of the criteria for a piece of work. Specifications for printing can include characterization-data, ICC-profiles, PDF preflight criteria, calibration targets for the print process, etc.

A Method is usually defined as a way, technique, or process for doing something. It is a recipe.

To use a cooking analogy - a standard represents the desired final outcome, for example a cake.The specifications describe the ingredients needed to make the cake. The method describes the steps required to make the cake. There can be many different methods to achieve the desired standard based on the specifications.

The most important standards for print production are:


• ISO 12647
 which describes color for different types of presswork (sheetfed, heatset web, coldset web, etc.). Of all of the standards within the Graphic Arts, what is of most importance to most printers and print buyers are contained within the ISO 12647 family.
ISO 12647 is broken down as follows

ISO 12647-1 Parameters & Measurement methods
ISO 12647-2 Offset Lithographic processes
ISO 12647-3 Coldset Offset Lithography on Newsprint
ISO 12647-4 Publication Gravure
ISO 12647-5 Screen Printing
ISO 12647-6 Flexo Printing
ISO 12647-7 Proofing process from digital data


• ISO 2846-1
 which describes ink color and transparency.


• ISO 3664 defines lighting conditions for viewing color copies and their reproduction with either incident or transmitted light.


• ISO 15930-X 
(PDF/X) for data exchange in print production.


• ISO 15076 for the ICC color profile format.


• ISO 12640 for the data format from which ICC profiles are calculated.


The most important specifications for standardized print production are:


PSO Process Standard Offset printing developed by FOGRA / bvdm / ECI

This implementation of ISO 12647-2 is included with most digital proofing solutions used in Europe and is pre-configured with the UGRA FOGRA Mediawedge for verification.
Grey balance target values in PSO are done by comparing K- and CMY-patches with similar grey side by side. PSO does not contain procedures and tolerances for judging grey balance by measurement.
PSO also includes the possibility of a certification for pre-press and printing.


GRACoL/SWOP managed by IDEAlliance


These standards take their basis from ISO 12647-2 but place a higher importance on grey balance during calibration and the press run compared with the PSO. Most proofing solutions for the North American market include the needed setup to produce proofs that represent the GRACoL/SWOP target.


System Brunner


System Brunner is a standardization method for print production. It places a very strong emphasis on grey balance (in combination with TVI and Solids) for controlling and certifying the press run. System Brunner is included with some printing press manufacturer's press control solutions.
It can also be combined with PSO, SWOP, or GRACoL.

There are various ISO 12647 standards according to the main types of printing methods. Here I will try and cover the essentials of just one of these - ISO 12647-2 - as an example of the type of specifications that guide printers to achieving the standard. Note that specifications do change over time, so, although the information I present is correct (as far as I know) the actual current published standards should be your guide.ISO 12647-2 specifies a number of process parameters and their values to be applied when preparing color separations for four-color offset printing by one of the following methods: heat-set web, sheet-fed or continuous forms process printing, or proofing for one of these processes; or offset proofing for half-tone gravure. Note that the specifications are based on plates imaged in a film, not CtP, workflow.

ISO 12647-2 is
▪ directly applicable to proofing and printing processes that use color separation films as input
▪ directly applicable to proofing and printing from printing formes produced by filmless methods as long as direct analogies to film production systems are maintained
▪ applicable to proofing and printing with more than four process colors as long as direct analogies to four-color printing are maintained, such as for data and screening, for print substrates and printing parameters
▪ applicable by analogy to line screens and non-periodic (i.e. FM) screens.

ISO 12647-2 Type 1 for offset lithographic processes on gloss-coated paper specifies:
Ink: ISO 2846-1
Substrate: L* 95 a* 0 b* -2
Primary Colors (black backed): K: L* 16, a* 0, b* 0 , C: L* 54 a* -36, b* -49, M: L* 46, a* 72, b* -5, Y: L* 87, a* -6, b* 90
Secondary Colors (black backed): R (M+Y): L* 46, a* 67, b* 47 , G (C+Y): L* 49 a* -66, b* 24, B (C+M): L* 24, a* 16, b* -45, C+M+Y: L* 22, a* 0, b* 0
Solid ink densities: (informative information)*
Halftone screen: 133 lpi, 150 lpi, 175 lpi, 20 micron FM
Dot Gain/TVI: 12 -16% or 18 -22%
Grey Balance: 25%-19%-19%, 50%-40%-40%, 75%-64%- 64%
Neutral definition: substrate or equivalent tone of black
ISO profile: ISOcoated_v2_eci.icc
Characterization data: Fogra39L.txt

GRACoL 7 The General Requirements and Applications for Commercial Offset Lithography publication that is a common reference in North America and is based on ISO 12647-2 specifies:
Ink: ISO 2846-1
Substrate: ISO 12647-2
Primary Colors: ISO 12647-2*
Secondary Colors: ISO 12647-2*
Solid ink densities: Not specified
Halftone screen: 175 lpi AM round dot
Dot gain/TVI: Not specified - replaced by Neutral Print Density Curve values: @ 25% Grey: CMY .25/K .22, @ 50% Grey CMY .54/K .50, @ 75% Grey: CMY .90/K .90
Grey Balance (required): 50%-40%-40%
Neutral definition: a* 0 b* -2
ICC profile: GRACoL2006_Coated1v2.icc
Characterization data: GRACoL2006_Coated1

Some peculiarities of ISO 12647-2 and GRACoL 7

Where GRACol 7 differs from ISO 12647-2 (as per the implementation guidelines of PSO (Print Standard Offset-print)) is the method used for adjusting the mid-tones. The PSO advises adjusting the inking until the TVIs of CMY come close to their aims, while GRACol 7 would have the neutral densities of the CMY and the K grey patches brought close to the prescribed aim values regardless of the individual TVIs that result. In practice this means that each color will have a different TVI curve to achieve the neutral grey. GRACol 7 allows for deviation of primaries in order to obtain grey balance.

ISO 12647-2 includes the following chart of dot gain/TVI curves:There are a few peculiarities with this chart. First is that there is no definition in ISO 12647 of what printing condition the letters "A" through "H" represent.** ISO 12647 does not clearly state whether these dot gain curves are intended to be tone reproduction targets or aim points or simply what you get when you use linear film to make printing plates. It appears that, because the specifications state that "direct analogies to film production systems are maintained" the intent is to use these curves as the reproduction targets. To, me, the idea of having different tone reproduction curve targets for presswork for different processes or different halftone line screens is counterproductive to standardization.

Resources:

Data set/s for profiling, separation, and proofing
ECI www.eci.org Profiles based on FOGRA data sets
FOGRA www.fogra.org Data sets that closely comply with ISO 12647
GRACoL http://www.idealliance.org
IFRA www.wan-ifra.org Profiles based on ISO 12647-3 (Newsprint)
SNAP www.naa.org SNAP profile
SWOP http://www.idealliance.org

Part 1 on this topic can be viewed by clicking HERE

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*Standards documents include two broad classes of information: "normative" and "informative"
Normative elements are defined as "elements that describe the scope of the document, and which set out provisions". Provisions include requirements that convey criteria to be fulfilled if compliance with the document is to be claimed and from which no deviation is permitted.

Informative elements include supplemental information such as additional guidance, supplemental recommendations, tutorials, commentary as well as background, history, development, and relationship with other elements. Informative data is not a requirement for compliance with the standard.

**As near as I can guess (so I may be wrong), here are the printing conditions represented by the letters "A" through "H" in the ISO dot gain chart. The curves are organized from the bottom up. They sometimes do double duty.

So:

A is the curve for CMY for Coated positive plate (ISO Coated v2 and FOGRA 27, FOGRA 39 etc)
B is the curve for K for same above condition

B is also curve for CMY for Web (paper type 3)
C is the curve for K for uncoated

C is also the curve for CMY for paper type 4/5 (uncoated and uncoated yellowish)
D is curve for K for same above condition

F is the CMYK curve for 20 micron non-periodic/FM screening

E, G and H are unknown (by me anyway). I believe that "H" has been dropped from the latest ISO 12647 document so these may no longer be in force.

Technical tips for creating brand colors

Color is one of the most critical components in creating brand identity and while there is a fair amount of information on the psychological and cultural aspects of color - there's very little information on the technical issues that need to be considered when developing a custom or brand color.

Brand colors are custom (a.k.a. line, spot) colors that are any single color (typically other than cyan, magenta, yellow, or black) that are usually printed as a solid area of ink on a dedicated press unit.

There are two types of custom colors -
1 Proprietary
2 Referenced.

Proprietary custom colors are colors that are created by the brand owner or their creatives. Coca-Cola red and Kodak yellow are examples of proprietary brand colors.
Referenced custom colors are usually published in color palettes that are to be used by creatives to specify spot colors.

The main brands of referenced custom color palettes are:

Pantone, the dominant spot color printing system in the United States and Europe.
Toyo, a custom spot color system that is popular in Japan.DIC, Dainippon Ink & Chemicals, Inc., another popular Japanese custom color system.
ANPA a palette of 300 colors specified by the American Newspaper Publishers Association for spot color usage in newspapers.
HKS Hostmann-Steinberg Druckfarben, Kast + Ehinger Druckfarben und H. Schmincke & Co. a custom color system containing 120 spot colors and 3250 tones for coated and uncoated paper.
The main benefit of creating a proprietary brand color is that it is unique to the brand thereby enhancing the brand's unique identity. The downside is that the creatives/brand owner are required to create their own system of specifying, communicating, and manufacturing the color.

The main benefit of using colors from a reference custom color palette is that the system of specifying, communicating, and manufacturing the color has already been built. The downside is that the color is not unique to the brand and can be used by others, potentially creating confusion in the marketplace.

When creating a new proprietary custom colors to be used for brand identity keep these technical tips in mind:

1- Humans have very good color discrimination for greens and much less for blues, reds, yellows, and purples.This means that they can more easily distinguish between subtle differences in two similar greens than they can two similar reds. It also means that there are more green custom color options than there are red.

2- In offset lithography, the range of possible greens is larger than that of reds, blues, and oranges

3- Humans have poor color discrimination when hues are very saturated - I.e. saturated colors will tolerate greater variation in reproduction before a color shift is noticed.

4- RGB, CMYK, and Hexadecimal values do not actually define colors because those values are device dependent. I.e. it does not, for example, tell us the specific hue of the Cyan ink being used - a factor that will change depending on the ink manufacturer.A demonstration by Flint ink of the influence on ink color resulting from differences in the substrate upon which the ink is printed.
So, a color defined using CMYK values will also look like a different color when printed on newsprint, in a magazine, or in a brochure due to the differences in the specific CMYK inks used and the substrates they are printed on.
Instead, define the color using CIEL*a*b* reference values since these are device independent. If RGB and/or CMYK values must be provided then make sure that the version or source is included (e.g. sRGB, Adobe 1998 RGB, CMYK/SWOP, CMYK GRACoL 7, etc.) to help minimize variation.

5- Confirm that the proposed custom color is within the color gamut of the expected most used reproduction process.An application like Chromix ColorThink enables the CIEL*a*b* values of the custom color to be compared with the color gamut of the system that will be used to print it and determine if it is reproducible or not - i.e. in, or out of, gamut.
If the custom color is within gamut, it means that it can be simulated by mixing screen tint percentages of the primary inks of the print process.

6- Make sure, by testing, that the ink pigments used in the custom color will not shift hue because of heat e.g. during lamination or react with other inks or to oxygen e.g. Reflex Blue.

7- Avoid using fluorescing agents in the ink.

8- Use certified sample color swatches and CIE L*a*b* values to communicate color globally.Ideally the sample swatches should be as large as possible since the perception of color changes with coverage area. Also include a "Hi-Lo" reference which shows how much darker or lighter the color can be and still be in specification. If possible, include a CIEL*a*b* Delta E value for how far the hue of the color can deviate while still being within specification. Include the information about how the Delta E value is to be calculated (e.g. Delta E 98, Delta E 76, Delta E CMC, etc.)

9- Prevent brand bloat by consolidating/rationalizing custom color libraries. Retire old colors and consolidate colors that are very similar.

Addendum
A number of readers questioned my statement that humans have very good color discrimination for greens and less so for other colors. In the below video Eric Fossum, image sensor engineer and primary inventor of the CMOS sensor used in digital cameras, mentions the color sensitivity of the human eye during a recent talk at Yale University.

E Ink Color Display - handicapped because of a fundamental color mistake?

E Ink Inc. whose Pearl greyscale displays are used in all the major e-reader devices have introduced a color e-paper display. If successful it may also compete against the new class of tablet computers such as Apple's iPad.

But is the color display handicapped because its engineers made a fundamental mistake in color technology?

E Ink's new Triton display will come in 5-, 7-, and 10-inch varieties, and E Ink seems to think that it will be instrumental in establishing digital newspapers and periodicals.It is claimed to be able to display “thousands of colors,” specifically 4096. However the color is extremely desaturated even in their carefully presented marketing materials. The display's lack of color saturation may actually reveal the cause of the problem.

How the display works

E Ink is short for “electrophoretic ink”. Technically speaking, charged pigments suspended in a clear liquid micro-capsule respond to a voltage that moves black or white pigments to the screen’s foreground.The technology differs from traditional displays because electrophoretic displays reflect light, rather than emitting it. Whereas computer displays and mobile phone screens rely on a backlight to illuminate pixels of different colors, E Ink technology leverages ambient light just like ink on paper.

With the E Ink Triton color configuration, a thin transparent colored filter array (CFA) is added in front of the black and white display. Now the display can also reflect color.The CFA consists four sub-pixels – red, green, blue, and
white – that are combined to create a full-color pixel. The result? A low-power, direct-sunlight, readable color ePaper display.

So what's the problem?

Emissive color displays like those used in LCD computer displays and televisions are based on the additive color model and use red, green, and blue light to produce the other colors. Combining one of these additive primary colors with another in equal amounts produces the additive secondary colors cyan, magenta, and yellow. Combining all three primary lights (colors) in equal intensities produces white. Varying the luminosity of each light (color) eventually reveals the full gamut of those three lights (colors).The additive color model used by emissive color displays uses combinations of red, green, and blue primaries.
On the other hand, reflective color displays like newspapers and magazines use the subtractive color model which starts with light, presumably white light. Colored inks, or filters, between the viewer and the reflective surface subtract wavelengths from the light, giving it color. In most color printing, the primary ink colors used are cyan, magenta, and yellow.The subtractive color model used by reflective color displays uses combinations of cyan, magenta, and yellow primaries.
E Ink's Triton color display, although a reflective device, uses the primary colors of emissive devices - red, green, and blue rather than cyan, magenta, and yellow. The result is very poor color saturation and very much reduced color gamut.Triton color display screen captures - note the absence of Yellow - a color that cannot be achieved with combinations of red, green, and blue filters in a reflective, subtractive color-based display system.


An E Ink video explaining the RGB(!) display technology.
Did the engineers made a fundamental mistake in their choice of color technology?

Mystery of the Lagorio Chart - Mapping the human tone response

Below is a "Lagorio Chart." The black line represents where the grey tone appears visually equal in luminosity to the color. It is the map of the tone to color response of the human eye.It was published in "The Complete Amateur Photographer" by Dick Boer, 1948. The idea behind its use was to determine how well the panchromatic film that the photographer was using translated color according to how the human eye sees that relationship.

The test method was quite straight forward. The photographer would take a black and white photograph of the Lagorio Chart using panchromatic film and then make a print of that image. The photographer would then plot a curve on the photographic print where the grey patches matched the color bars (now rendered in grey) - plotted using a dotted line in the image below:This chart was also recommended by prepress personnel to help them translate color images into black and white halftones while maintaining the appropriate tonal relationships. Indeed this principle could still be used today to make conversions from color images to black and white in applications like PhotoShop.

So what's the mystery? Well, this is the only chart I've ever seen that plots the grey scale response of human vision. None of my other graphic arts books (and I have quite a library) contains a chart like this. Nor does there seem to be any information on the internet about Lagorio and/or this chart. Who was Lagorio and how did he/she determine the human eye's tone response? Was it just what he saw, or were committees of experts involved? The mystery remains.

If you can shed any light on the Lagorio Chart - please contact me via email (pritchard gordon @ gmail (dot) com) and I'll add an addendum to this post.

The Color Bar

Color bars (a.k.a. color control bars, color control strips, or proofing bars) are essentially test targets that are used to measure print and/or proof attributes. Normally, but not always, it is printed in the trim area of the press sheet.Typical placement of a color bar on an offset press sheet - at the trailing edge (back end of the sheet).
However, it can take many different forms - sometimes hard to recognize - but always serving the same purpose.

Sometimes the "color bar" is incorporated within the graphic design of the publication. In this case the color makeup of the title (Cyan) and section headers (Blue, in this example, - Magenta overprinting Cyan).
Sometimes it is hidden in the spine (in this case the grey line running from top to bottom on the front edge of the photo).
While it is certainly possible to measure the color of the actual live image area, the technology is expensive and, as result, few printers are fortunate enough to have it at their disposal. Also, measuring the live image area doesn't provide as much useful information as a color bar can. Color bars therefore act as proxies, or substitutes, for the live image area as well as provide additional data.

The logic behind color bars

1) Unlike the live image area of the press sheet, color bars are consistent job to job. Therefore they are more efficient at providing a benchmark and can be used to track trends in variation over time.

2) Color bars can be tailored to meet the needs and measurement capabilities of individual print shops.

3) Color bars may be used to measure all aspects of the "print characteristic" - solid ink density, overprinting (ink trapping), dot gain, grey balance, as well as issues such as slur and dot doubling.

4) Color bars can reveal issues with ink hue, blanket condition, impression cylinder pressure, etc.

5) They can be used forensically to help understand why a specific job did not meet expectations.

6) They are efficient since, unlike the live image area, they are a constant made up of well defined elements that continue from proof to press sheet.

Solid ink density
A printing press is essentially a complex machine for laying down a specific film thickness of a specific color of ink onto a substrate. The ink is metered out in zones across the width of the press sheet according to how much ink coverage is required for each color in each zone.Therefore, for most press operators, the minimum requirement for a color bar is that it contains solid patches of the inks that will be printing since solid ink density is the only thing on press that an operator can adjust while the press is running.Those solid patches are then repeated over the width of the press sheet so that each ink zone is represented by at least one complete set of patches - containing one patch for each color being printed.
Information provided by only using solid ink density targets in the color bar
In this example, cyan is misregistered while the black printer is over emulsified (fountain solution breaking down the ink).
1) Provides a solid ink density value, measured using a densitometer, to determine if the press sheet is conforming to published industry, or shop specific targets.

2) Is an indirect, but practical, method of determining optimum ink film thickness and hence the balance of maximum color gamut without introducing image degrading inking issues such as slinging/misting.

3) The balance of the primary solid densities determines the hue of the overprints - i.e. the SID of magenta and SID of yellow determine the hue of the resulting red.

4) Indicate misregistration which can then be examined in the live image area.

5) Reveal defects such as slinging/misting/tailing, over emulsification, slur, doubling.

6) If records are kept, the hue of the ink currently on press compared with the hue of ink used in the past to determine if there is any contamination, change in color due to ink batch differences, etc.

Forensic targets on color bars are image elements that are typically not measured by the press operator unless there is a problem in aligning presswork to the proof. If that happens then these targets may provide useful information as to the cause of the problem.

Two-color overprint ink trapping targets
Ink "trap" is an objective indication of the ability, or inability, of a printed ink to accept the next ink printed compared with how well the substrate accepted that ink. Poor ink trapping results in presswork color shifts in reds (magenta plus yellow), greens (cyan plus yellow), and blues (cyan plus magenta) as well as a loss in total color gamut.
The two-color overprint solids allows for the objective measurement and evaluation of ink trap efficiency as well as the overprint hue error and greyness.
Typical trap values for three print conditions running a CMY ink sequence with Black first or last down:
Offset sheetfed: R=70, G=80, B=75
Heatset web offset (publications): R=70, G=87, B=72
Coldset web offset (newspaper): R=50, G=89, B=50

Slur and doubling targets
Slurring and doubling are print defects that occur when halftone dots and type blur as a result of a slight second contact or movement between press cylinders or the paper and blanket. (More about slur HERE and doubling HERE)
There are many different styles of slur and doubling detection targets. Here are two of the most popular:Of course, every halftone dot or letter character on the printed sheet will reveal slur and doubling, however the targets in the color bar signal the defect easier and quicker.
Grey balance targets
Grey balance targets are made up of a patch of three screened process colors that are balanced so as to appear as neutral grey under standard printing conditions. They are typically printed adjacent to a black screen tint of a similar value to allow for a quick visual, or measured, evaluation of how grey balance has shifted.Grey balance targets can be useful since variation in any of the three process colors because of dot gain, slur, doubling, density, trapping, and registration will be reflected by a shift in hue away from neutrality. The 3/C patch will take on a bluish, reddish, or greenish color cast.The idea behind this target is that any grey balance color shift away from neutrality suggests a possible color shift in the live image area. However, in production printing the grey balance target may not be a reliable indicator of presswork issues.

Other targets
Other targets that may be included in the color bar are:

Dot gainThese targets are intended to capture dot gain variation information. The dot gain targets may consist of just two patches for each process color to measure the dot gain a one location on the tone scale, or, with the addition of more patches, to measure the dot gain at the quarter, mid, and three-quarter tone values. Dot gain can be useful because issues like slur, doubling, or incorrect solid ink density, will be reflected by a variation in the measured dot gain.

Brown balance targets
Brown balance patches are similar to grey balance patches in function except that they are made up equal percentages of cyan, magenta, and yellow. Unlike grey balance patches which allow the press operator to make a subjective visual assessment of hue shift, brown balance patches can only be evaluated objectively with instruments.

ProprietaryProprietary targets such as that used by System Brunner are typically used to drive on-press closed loop color control systems.

Spot colorIf a spot or brand color is being used then it will warrant at least a solid patch in the color bar so that its solid ink density can be measured. Space permitting, the solid patch will be adjacent to a screened back patch so that dot gain information can be measured.

For process control, color bars should be included on every proof and press form of every job. If that is not possible because there is no room on the sheet (as often happens in newspaper work) then there are several options;

1) Run color bars on occasion by including it in the live image area.With the publisher's permission if required.

2) With the print buyer's permission, incorporate color bars test elements into the graphic/editorial design of the printed piece (see the USA Today example in Part 1).

Color bars are not a requirement for quality printing, however, they are key to making proofing and printing more efficient and effective while reducing overall production costs.

Presswork should be run "to the numbers" i.e. the solid ink density aim points, at which time the presswork should align to the signed-off proof. At that point the press operator should be free to make any needed ink key adjustments to refine the match. The color bar then becomes a record of initial match and needed adjustments. That information can be used in statistical process control to spot any trends, or issues, revealed by the kind of ink key moves that are made over time.

Color bars can be placed anywhere that they fit on the press form, including the lead and trailing edge as well as across the center of the form. In fact, placing it in the center of the form parallel to the inking rollers is ideal, since there is less likelihood of seeing the variation that occurs at the lead and trailing edges. Color bars can even be placed in the gutter inline with the direction of the sheet through the press, although doing so is not optimal since it provides information from only one ink key zone.

Ideally the color bar should use the same halftone screening as the live image area and have had the same press curve applied.

The issue of metamerism in print production

With print, each medium in the production process from original art to image capture, monitor display, proof, and final presswork has its own unique spectral characteristics. The majority of color reproductions utilize cyan, magenta, yellow, and black inks or colorants. But none of those inks are exact spectral matches to the media originally used to produce the original art. As a result, the inks used to create color reproductions are combined to simulate an artwork, but only under one industry standard light source - referred to as "D50" or "D65".

During production the integrity of the reproduction of artwork is monitored by making comparisons, for example, original to its copy or proof to presswork. The two colored objects are referred to as a metameric pair if they match under at least one combination of illuminant and observer and not match under at least one combination of illuminant and observer. They must also have different spectral response curves.

So, the phenomenon of metamerism begins with comparing a pair of colored objects. For example the color of the back door of this truck compared with the color of the rest of the truck.
In the truck example the pigments used in the paint were not the same for the back door compared with the rest of the truck. The two colors would have matched under the artificial lighting that was used when the door was painted. However, under sunlight conditions the door and body no longer match causing "metameric failure."

In this case metameric failure is a benefit to the prospective customer since it warned that the door was painted at a different time from the rest of the truck. Possibly it had been damaged and subsequently repaired. Unfortunately the effect of metameric failure in print production usually causes problems rather than benefits.

How metameric failure impacts print production

There are four types of metameric failure commonly encountered in print production.

Sample metameric failure This is the most common cause of color matching problems. The truck example above is an example of sample metamerism. Because proofs and press sheets form metameric pairs, this problem typically shows up when presswork matches the proof in the light booth at press but no longer match under the lighting conditions where the presswork will normally be used, e.g. a package in a store, or brochure in a home environment. Other examples of sample metameric failure include product samples (e.g. fabric) compared with their reproduction in proofs, presswork, or computer displays. Or process color screen tint builds. They may match under one lighting condition but not another. Sample metameric failure can also happen if two prints using very different technologies - such as offset print vs silkscreen print - are compared under different lighting conditions.

Observer metameric failure This can happen because of differences in color vision between observers. Although the common cause is colorblindness, it is not uncommon among "normal" observers. As a result, two spectrally dissimilar color surfaces may produce a color match for one person but fail to match when viewed by a another person. Observer metameric failure is the reason there were 31 individuals tested to derive the original 1931 "standard observer" values adopted by the ISO and that are still used today as the basis for the majority of color science.

Field-size metameric failure This occurs because the relative proportions of the three light sensitive cone types in the retina of the eye vary from the center of the visual field to the periphery. The result is that colors that match when viewed as very small, centrally fixated areas may appear different when presented as large color areas. This is the reason why color painted on a wall may appear different than the paint chip used to select the color even though they match when the chip is placed on the wall. In print production field-size metameric failure typically occurs when small PMS swatchbook samples are used to specify a PMS color that will cover a large press sheet area.

Geometric metameric failure Normally, material attributes such as translucency, gloss or surface texture are not considered in color matching. However here, identical colors appear different when viewed at different angles, distances, light positions, etc. Geometric metameric failure is most often seen when using metallic inks or paper, and specialty ink coatings or papers.

Tips for dealing with metameric failure

1. Be aware that it exists and may be the "simple" issue causing any color match issues.

2. If color needs to align across different lighting conditions choose pigments carefully or make the ink formulator aware of that requirement.

3. Control your lighting conditions - both for producing prints, final viewing (where possible), and for critical evaluation. The industry standard light source is referred to as "D50" or "D65" (5,000° Kelvin (North America), 6,500° (Europe).

4. Invest in PIA/GATF RHEM light indicators for everyone in the production chain that is involved in evaluating and approving color. RHEM light indicators are small (2" x 3/4") paper stickers with a unique printed design that uses metameric failure to indicate whether or not the viewing conditions are 5,000° K or not.Stripes appearing in the RHEM sticker indicate the lighting conditions and therefore whether a color evaluation can be made.
The stickers can be affixed to proofs or simply carried in a protective wrapper in purse or wallet.

5. Printshops should have viewing areas away from the press that allow print customers to view the presswork under typical lighting conditions (fluorescent and incandescent).

6. Be sure that all instruments (e.g. spectrophotomers) that are used for color evaluation are set to the same standard illuminant, D50 or D65, and same observer angle (typically 2°).

What is wrong with this scene?