Speckles in presswork - secret of the yellow dots

Most manufacturers of laser toner printers have embedded within them a technology that leaves microscopic yellow dots on each printed page. The dots are intended to identify the date and time of the printed sheet (if known by the printer itself) as well as the printer's serial number in order to identify the owner and location of the printer.
On the left, a close up of the "secret" yellow laser dots. On the right the same dots viewed under a blue light to enhance contrast and visibility.
The dots, which are normally invisible to the naked eye, form a code which is used by authorities such as the U.S. Secret Service to investigate the printing of counterfeit money made with laser printers.
The secret yellow dots are typically too small to be seen at normal viewing distances.
The yellow dots are a bit larger than the halftone dots used to create the actual image.
Unfortunately, if the laser printer is not calibrated properly, or depending on the design of the graphic being printed, the yellow dots may be dark enough to be visible. Also, the dots may affect the reporting integrity of color measurement instruments – e.g. a cyan patch intended to be 100% cyan only may contain yellow security dots and cause a slight green shift.

Specks in presswork - ink in the non-image area

Press operators are often seen bent over a press sheet examining it under a loupe. One of the things they should be looking for, but often miss, are specks of ink appearing in the non-image area of the presswork.A 20x enlargement of solid ink patches showing small speckles in what should be unprinted paper. The pale thin lines are paper fibers.
(Click on image to enlarge)
A 200x enlargement of the above image showing the small speckles of ink more clearly. The pale thin lines are paper fibers.
(Click on image to enlarge)
There are several possible causes of this problem.

Tinting (also called toning). This is caused by contamination of the fountain solution by either ink, or some coloring matter from the ink. Since fountain solution is all over the non image area, any coloration will be likewise. It is usually caused by the fountain solution breaking down the ink but it can also be caused by the plate. Usually though, tinting will appear more like a very pale wash of color over the non-image area rather than discrete specks of ink on an otherwise clear background.

Redeposit. This occurs when specks of developed/removed coating are re-deposited onto the plates later in the processing cycle. It's typically due to dirty rollers or contaminated rinse water, but can be exacerbated by hard water in the rinse or improper exit roller pressures (allowing more developer to carry-over into the rinse). These specks of coating adhere to the plate and accept ink and print on press.

Incomplete processing Problems with the mechanics of the plate processor like bad brushes and/or pressure may not scrub the plate well enough to remove the particles of coating from the unexposed areas of the plate. Typically though, there would be a more general toning in those cases (but not always).

In general, if the specks appear only in one color then that press unit is more likely the cause of the specks and it's also more likely that the problem is tinting/toning. However, if the specks appear in all four colors then it is more likely that the plates are the cause of the problem and it's important that the press operator inform prepress about the issue.

From the print buyer's point of view, there will likely always a few specks appearing in the non-image areas of presswork. If this is a critical concern, as in security printing, then it is best to discuss the issue with the print supplier and perhaps agree to what would be an acceptable number of specks per square inch/centimeter.

Calcium carbonate - the problem with better quality paper

Calcium carbonate is used as a filler in the basesheet and in the paper coating as a pigment. It provides brightness and a more blue-white shade than clay does. Calcium carbonate is used in neutral or alkaline paper making, which results in a more permanent sheet than acid paper making by reducing the yellowing and brittleness of paper as it ages.Trace amounts of calcium carbonate can even be found in some ink formulations where it is used as an extender. Higher levels are typically present in magenta ink. Calcium carbonate buidup on the blanket often shows up as a hole in the center of halftone dots - especially in smaller, or highlight, dots as in the example above.
The upside in the move from acid (clay filler) to alkaline (calcium carbonate filler)
Unsurprisingly, the benefits of calcium carbonate has resulted in a move, that began in Europe, from acid paper toward alkaline paper.

Alkaline paper provide several advantages over acid paper:

• It's less polluting to the environment
• Has better permanence
• Provides improved sheet strength
• Uses fewer trees per ton of paper produced
• Has increased opacity and brightness
• Faster ink set for quicker turn around
• A more cost-effective paper manufacturing process

Today, almost all of the North American uncoated wood-free sheet capacity uses an alkaline or neutral papermaking process with calcium carbonate as a filler and pigment.

The downside
However, alkaline papers can create a whole set of printing issues for printers. Calcium compounds can leach out of the paper during the printing process. This leaching out can be exacerbated by highly acidic or overly aggressive fountain solutions especially on uncoated papers. When this happens, the calcium carbonate pigments migrate to the upper form roller. Once there, they are milled into the ink and dispersed throughout the dampening system build up and may overwhelm the printing system.

The impact of calcium carbonate leaching can include:

• Tinting on the printed sheets
• Toning on the plate
• Blanket piling and picture framing effect
• Build-up on non-image area of the plate weakening receptivity of water (scumming)
• Roller glazing
• Contamination of fountain solution and increase pH and conductivity
• On negative plates, the calcium carbonate crystals from the paper (two to three microns in diameter) may accumulate on small dots and cause blinding.

Calcium carbonate issues are most often experienced in high volume web printing with uncoated paper where calcium carbonate is used as a relatively unsealed basestock filler.

Symptoms of calcium carbonate contamination may include:

• Progressively poor ink transfer usually seen as dot sharpening
• Ink roller stripping
• Fountain solution progressively becoming more alkaline (if it's not buffered for alkalinity).
• High conductivity gain of fountain solution
• Excessive foaming of fountain solution.
• Build-up of calcium on the ink rollers. This typically appears as a white haze which is not easily removed with conventional roller wash.
• Calcium deposition on the blanket surface (a white haze which cannot easily be removed by plain water) which interferes with the ability of the blanket to transfer ink properly and print a sharp dot with clean background.
• Build-up or piling in the non-image area of the blanket.
• Progressive toning or scumming as a result of increased alkalinity, poor water receptivity, poor ink transfer, and accelerated plate wear.
• The sizing particles attached to the calcium carbonate pigments may activate the ink driers prematurely, resulting in either plate scumming or plate blinding with blanket and roller glaze impeding the transfer of ink which in turn necessitate frequent, but ineffective, wash-ups.
• Problems specifically with magenta or red pigmented inks.

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?

Fade to black - ink permanence

Unfortunately, ink, like most things in life, is not permanent. The inks used in print production will all fade over time. The main cause is exposure to light (especially UV), which causes the ink/paper system to oxidize. When ink is oxidized it fades. Fading is much more complicated than is usually realized as it depends on environmental factors (light, heat, humidity,), the particular pigments being used, and the substrate the ink was applied to.

Ink manufacturers use fadeometers, along with known ink pigment characteristics, to test fade resistance by exposing the print to light radiation produced from a carbon arc or xenon tube. The arc emits an intense actinic light which in a matter of hours approximates the destructive effect of a much longer period of ordinary daylight. Although it does not exactly duplicate the effect of prolonged exposure to natural light, it is still an effective indicator of the degree of light stability and of the comparative resistance to fading. The results are interpreted with the aid of a chart that correlates the number of hours a printed sample lasts in the fadeometer to the equivalent exposure to direct sunlight taking into account the amount of UV light that different regions receive based on their latitude.

If resistance to fading is an important criteria for a print project, the best source of information is the vendor supplying the inks. They will know the characteristics of the pigments in their ink formulations and can suggest alternatives that may provide better fade resistance - though often at the expense of some other attribute like rub resistance, color vibrancy, or cost.

You can also do a simple test yourself. Simply take a presswork sample and cover half (front and back) with heavy black card. Then attach the sheet to a window.The covered section of the press sheet is the control against which you can compare the fading of the exposed part.
Original image
After 1 month
After 12 months
After 18 months
After 24 months
Some typical fade resistance numbers for sheetfed 4/C process inks based on outdoor exposure near the equator:

• Black (pigment black 7)
- Tint - Max tolerance: greater than 12 months.
- Fadeometer, Max tolerance: greater than 240 hrs.

• Process Cyan (pigment blue 15:3)
- Tint - Max tolerance: 24 months with fading
- Fadeometer, Max tolerance: 120-160 hours shows fading and loss of gloss

• Process Magenta (pigment red 57)
- Tint - Max tolerance: less than 1 month with fading & loss of gloss
- Fadeometer, Max Tolerance: 5-25 hours shows fading and loss of gloss

• Process Yellow (pigment yellow 12)
- Tint - Max Tolerance: less than 1 month with fading
- Fadeometer, Max Tolerance: 2-30 hrs shows fading and loss of gloss

How lightfastness is measured


The "Blue Wool Scale" is the internationally recognized method of quantifying lightfastness, defined under the British Standard BS1006. The scale consists of 8 different strips of wool, each dyed with a blue dye of differing lightfastness. The scale ranges from 8 (excellent – very low rate of fading) to 1 (very poor – extremely fast fading). The blue wool scale is not a linear scale but is rather logarithmic, so that each increase in level is greater than the previous.

When exposed in the same manner as the print for the same length of time, the level of fading of the printed solid is compared to that of the equivalent strip of wool to provide a value indicating the lightfastness of the print.

The "Wool Scale" lightfastness classifications are:
WS 1 - very poor
WS 2 - poor
WS 3 - moderate
WS 4 - fairly good
WS 5 - good
WS 6 - very good
WS 7 - excellent
WS 8 - maximum lightfastness

Tips for the printer:

• When interpreting degrees of lightfastness into production requirements - real-world conditions need to be taken into account. For example a paper that contains a high degree of wood fiber will soon yellow and therefore effect the color of ink that overprints it - even if the ink has a high WS rating.

• A higher ink film thickness than indicated in the standard specifications will result in an increase of the lightfastness of the print because there will be more pigment particles in a given area to withstand the destructive influence of light. The same applies to a higher pigment load ink. On the other hand a thinner ink film thickness will reduce lightfastness. Also, lightfastness in halftone screened areas is generally lower than in the solids.

• Varnishing and lamination of presswork will generally improve its lightfastness. Specific over varnishes exist which contain UV inhibitors and high-grade resins. These can increase the lightfastness of presswork, however, they will not prevent ‘weak’ pigments from fading, merely slightly increase the time they take to fade.

• If two or more printing inks of different lightfastness properties are mixed, the low WS rated one is not improved by the high WS rated one. Instead the low WS rated one lowers lightfastness of the high WS rated ink. Effectively the ink of the lowest lightfastness determines the lightfastness of the mixed Ink.

• Lightening of an ink with transparent white will, in most cases, diminish its lightfastness. Since white pigment does not fade easily, pastel colors with a small concentration of colored pigment and a large concentration of white will fade rapidly to white. For similar reasons, large quantities of varnish should be avoided in colour matches for presswork exposed to sunlight.

As a general guide, lightening with transparent white at a ratio of 1:1 will reduce lightfastness by 1 grade. Lightening with transparent white at a ratio of 1:3 will reduce lightfastness by 2 grades.

• Lightfastness of presswork exposed to sunlight will be lower near the Equator and higher as one move towards the Poles.

• In the northern hemisphere lightfastness of presswork exposed to sunlight will be lower in the summer and higher in the winter.

Putting a glow in your presswork - OBAs and black light posters

Most printers who are faced with a printing job that's intended to glow under black light tend to think only about the issues of printing with fluorescent inks (see the post HERE). However, there is another important item that needs to be considered and that is the effect that the amount of, or lack, of OBAs (Optical Brightening Agents) in the paper will have on the final result.

For example, viewed under a black light this poster "glows" in an expected way:And it will look similar, except for the glow effect, under normal room and black light conditions.

However this poster which has large areas of white, i.e. unprinted paper, looks very different under normal house light:compared with being viewed under black light:
The difference in appearance is caused by the amount of OBAs in the paper. In this example, the paper contains low/no OBAs. Under normal home lighting the paper looks white and the fluorescent inks fairly bright. However, under black light the inks glow brightly but the paper which contains low/no levels of fluorescing agents goes dark - there is effectively no light for the paper to reflect.

This difference in color response can be used creatively or it could destroy the intended look of the poster as envisioned by the artist.
If a paper with high levels of OBAs is used instead, then the appearance of the image would be preserved under black light:
So, when quoting a "black light" job consider the amount of OBAs that the paper contains because it can have a profound effect on the final result. If the paper will have 100% ink coverage then choose a paper with high OBA content to assist in the final glow effect. If the design includes areas of white, then discuss the issue with the original designer and choose a paper that has high, or no OBA, content according to the final result the designer is trying to achieve.

To determine the relative amount of OBAs in the paper, view a sample using an inexpensive fluorescent type black light:

Fluorescent inks

The pigments in fluorescent inks work by absorbing ultraviolet energy (invisible to the human eye), and transmitting it as longer waves in the visible spectrum.

Cyan, Magenta, and Yellow process inks can be replaced with their fluorescent equivalents for a strange, while at the same time, semi-natural look. Novelty effects in four color process printing can also be achieved by mixing 50% Pantone 803 fluorescent Yellow with 50% process Yellow and 50% Pantone 807 fluorescent Magenta with 50% process Magenta. Alternatively, using one fluorescent ink, usually Yellow or Magenta, in combination with process colors can add impact to the result or help compensate for a poor substrate. This is most often seen in newspaper work where fluorescent Yellow is sometimes used in place of process Yellow.

In addition to the process equivalent fluorescent inks there are some 10 base fluorescent ink colors for print application and which can be used in Hi-Fi image reproduction or as spot/line colors.

Although very bright appearing, fluorescent inks tend to be weak on press and hence should be printed at higher solid ink densities. They often require a double hit, especially on offset coated papers, to bring them up to full potential. They are well suited for gravure printing since that process can lay down a thicker ink film than offset. Note that ink drier additives may be required when running fluorescent inks on coated papers.

Fluorescent pigments, especially the red, are fugitive so exposure to sunlight will rapidly cause fading. Fluorescent inks are not formulated to resist high heat, so they are not suited to stationery that will be run through a laser printer or copier.

Note that the amount of optical brightners used in the substrate to be printed on will have an impact on the final result - see the post HERE for more details.

Ink savings using solid screening

Solid screening is a technique that reduces ink consumption (and associated costs) by punching holes – too small to be seen in the presswork – into graphics that normally would print as a solid 100% tone or color. This technique is best suited for newspaper printing where the combination of dot gain and absorbency of the paper hide the visibility of the holes in the final presswork.
In this example I've used the character "$" from the Bitstream "Vera" font**, however this technique can be used with any line/solid graphic. In order to create the holes, I've screened the letters from 100% solid to a 90% tone. The correct amount of screening back to use requires some experimentation as it is a function of the halftone screening and paper that is being used.


A - The original character (Bitstream Vera) at 10 pt.
B - The same character using the SPRANQ Ecofont*. This font is designed with holes within the letters to reduce inkjet ink consumption by approximately 15-20%. The font can also be used for offset printing, however, because of the size of the holes used, this font is limited to a maximum character size of about 12pt.
C - The same character but screened back to 90% using a 133 lpi AM halftone. Because the AM dot is quite coarse, this technique is best suited to sans serif sizes greater than 18 pt. otherwise the character become too broken up by the halftone screening.
D - The same letter but screened back to 90% using a 20 micron FM halftone. The high resolution FM dot allows this technique to be used with both serif and sans serif fonts ranging from about 9pt and larger.

For newspaper application, rather than using a halftone to screen back type, it may instead be worthwhile to develop a custom font or to modify the current publication font(s), and build holes directly into the characters in similar fashion to example "B" above.

* The SPRANQ Ecofont can be downloaded from: http://www.ecofont.eu/
** The Bitstream Vera font can be downloaded from: http://www.dafont.com/bitstream-vera-mono.font

Screening solid tone areas in order to reduce ink usage is not limited to flat tone areas or fonts (as described in part 1), the technique can also be used on halftones which are, after all made up of small areas of solid tone. Here is the original image of comedian Tony Hancock:Here is a close up of the original AM/XM halftone version of the image; (Click images to enlarge)
Here is the AM/XM halftone rescreened with a 2% AM halftone dot (applied to tones darker than 5%):A more sophisticated version of this method is used in Esko Concentric screening:
And here is the AM/XM halftone rescreened with a 2% FM dot (applied to tones darker than 5%):
Punching holes into halftones does add complexity in prepress and may not be possible with some workflows. However, it can be a useful strategy to reduce ink consumption in both black and white and color images for those systems that are able to screen bilevel halftones.

Hi-Fi color - 8 strategies to implementation

There are basically 8 established ways to print contone images with added vibrancy – i.e. Hi-Fi color. Most require a great deal of testing and experimentation. Many will be problematic from a proofing point of view, however, the testing process can often provide samples that can be used give buyers a good enough idea as to what their specific finished product would look like. Note that the extra vibrancy achieved on press with these processes is dependent on the gamut of the images selected for this process. Images that are already well housed within the standard cmyk color gamut will likely not benefit from the Hi-Fi gamut and therefore show no visible difference compared to a standard four color process image.

In order from simplest to most complex:

1) Increase solid ink density.
Solid graphic is 175 lpi gamut at standard SIDs. Translucent graphic is 175 lpi gamut at higher SIDs.
Solid ink densities can often be increased by about 20-30 points from industry standards on presses which have aqueous coaters. Curves are applied to plate to normalize dot gain (restore tone reproduction). Extra saturation affects all color areas on the page. Testing determines the max density that can be achieved before presswork color becomes unstable, or ink slinging or tailing occurs. Uses existing CMYK images. This is the simplest approach to add punch since the only thing in production that needs to happen, once testing is complete, is to have a curve applied to the plates and new SID targets communicated to the pressroom for jobs targeted for the extra vibrancy. A popular strategy because it does not require anything to change other than a curve applied to the plates. It will increase overall color saturation but may not increase the gamut in areas where CMYK is weak (oranges and purples). A more complete explanation of the process begins HERE. A variation on this method would be to run CMYK at normal SIDs and then do a second hit of CMY also at normal SIDs.

2) Use FM screening.
Solid graphic is 175 lpi gamut using standard inks. Translucent graphic is 20 micron FM screening gamut.
Going to a finer screen, either 20 micron FM or greater than 385 lpi AM/XM screening will provide about 10-15% greater gamut volume compared with 175 lpi AM/XM screening. The extra gamut will be available in one and two color screen tint builds only.


3) Big Gamut CMYK
Solid graphic is 175 lpi gamut using standard inks. Translucent graphic is 175 lpi gamut using wider gamut CMYK inks - Toyo Kaleido inks in this example.
This method uses higher pigment load inks, or spectrally purer colorants (and therefore more expensive inks). Examples are Toyo Kaleido inks and (BASF) Flint Novaspace f 2010 inks. Extra saturation affects all color areas on the page. This method uses existing CMYK images, however existing separations may produce unexpected results. From a production point of view, washups and ink change overs will happen when switching from regular CMYK to Big Gamut CMYK jobs.

4) CMYK plus "bump" (touch plate) color.
Solid graphic is 175 lpi gamut at standard SIDs. Translucent graphic is extra gamut resulting from the addition of a special Orange and special Blue.
Adds gamut only where needed (e.g. oranges, blues, etc.). Manual process in Photoshop to create 5th plate. Requires testing and experimenting to establish workflow. Uses existing CMYK images with added spot color channel to add extra vibrancy within specific images only. Note that the extra ink(s) will need to be formulated to wet trap, be screened, and have a dot gain similar to its closest process color. E.g. Red ink would mimic Magenta in lithographic performance. This method is usually used in fine art reproduction, catalogue, and automotive work to bring specific colors into gamut.

5) Swing process colors.
Solid graphic is 175 lpi gamut at standard SIDs. Translucent graphic is extra gamut in the blue range resulting from the substitution of a violet for the standard process Cyan.
This uses a standard CMYK ink set where one of the process colors, usually magenta but sometimes the cyan, is swapped out for an alternate. For example, the standard process magenta might be swapped out for a PMS Red 032, Warm Red, Rhodamine Red, or even PMS 2395. This distorts the entire gamut but can be very effective depending on image content. For example, a photo of an orange against green leaves would really pop if a warm red is used instead of a conventional magenta. This method is best used where there are no skin tones present since skin tones would look quite odd. Note that all image content is affected, including text. Requires a lot of experimentation and documented samples.

6) Big "H" Pantone Hexachrome.
Solid graphic is 175 lpi gamut at standard SIDs. Translucent graphic is extra gamut resulting from the use of proprietary Pantone Cyan, Magenta, Yellow, Orange and Green.
Uses a proprietary 6 color inkset with fluorescing agents in their pigments. Extra vibrancy affects all color areas on the page (images and text). Inks tend to have poor printability. Expensive. Manual process to do separations in Photoshop. It often delivers images that have an "artificial" look. Colors can appear garish rather than natural. Requires testing and experimenting to establish workflow. Complex separated workflow (DCS 2 files).

7) Small "H" Hexachrome.
Solid graphic is 175 lpi gamut at standard SIDs. Translucent graphic is extra gamut resulting from the use of Orange and Green.
Uses standard CMYK inks plus Orange and Green inks to expand Gamut. Uses Pantone Heximage software from Pantone to do manual separations to 6 color process in Photoshop. Extra vibrancy applies to images only. This method is popular in the label and packaging markets. It can be a good compromise compared to process 5. Complex separated workflow (DCS 2 files).

8) CMYK plus "extended" process colors.
Solid graphic is 175 lpi gamut at standard SIDs. Translucent graphic is extra gamut resulting from the use of Red, Violet, and Green "extended" process colors.
ICC profile based workflow. RGB in and separated to CMYKRG or CMYKRV, or CMYKRGB out. Fully automated process. Requires profiling the press using the appropriate inkset. Creating an RGB to CMYKXX separation profile. The profile is used by the workflow to separate the images as part of the process plan, as delivered to the workflow as a preseparated file. Extra vibrancy applies to images only.