Who is responsible for print shop color?

In basic terms:

It is management's responsibility (with input from prepress, press room, and sales) to establish what the presswork color targets and tolerances (dot gains, standards, specifications etc.) are for the presswork - because those are marketing/business decisions. Then provide the tools (training, resources, equipment) to allow prepress and pressroom to achieve those targets.

The responsibility of prepress is to align proofing to the target established by management as well as to maintain proofing within the tolerances established by management because tolerance targets are also marketing/business decisions. Prepress must also output plates that enable the press operators to align their presswork to the proofs with the press performing in a repeatable, stable, cost-effective condition.

The responsibility of the press operator is to manage the press in such a way that the films of the appropriate inks are laid down in a manner that meets the targets and tolerances (hue, trapping, etc.) established by management and that the halftone dots on the plate are reproduced with fidelity on the various substrates (avoiding slur, doubling, etc.). Also, the press operator needs to make sure that all press-related consumables (fountain solution, inks, etc.) are within the tolerances needed to achieve the management defined targets for pressroom output.

"DPI" and the misuse of graphic arts terminology

The prepress and press worlds are some of the worse misusers of terminology with the all too frequent resulting confusion in sales, marketing, specification, and production. Here is one of the most misused: "DPI" (or as it is spoken of in the rest of the world: DPCM).

"DPI" - Dots Per Inch is a term used for a variety of things that properly speaking it shouldn't.

DPI - when used to describe the resolution of a computer to plate imaging device or filmsetter. E.g. "This is a 2400 dpi CtP device."

"Dots" in this case refers to the laser "Spots" of energy that expose the printing plate or film. However, while DPI, identifies the number of dots per inch - it doesn't actually describe the resolution of the device or size of the spot of energy. Instead it defines the device's "addressability." In other words, dpi tells you how many locations per inch a spot of energy can be focussed on – not the actual size of the spot of energy.

This graphic shows plate media being exposed at 2,400 dpi by six different CtP devices:Note that they are all 2,400 dpi - that is that they all can hit the target location (address) with their beam of energy - however the exposing spots of energy are all different sizes, in this example ranging from about 2 microns on the left to about 30 microns on the right.

Resolution vs addressability is explained in more detail by clicking HERE.

DPI - when used to describe the resolution of an inkjet printer. E.g. "This inkjet proofer prints at 2880 x 1440 dpi."
In the case of an inkjet printer, the clue to this misuse of dpi to wrongly mean resolution is revealed with asymmetrical dpi specifications. So, an inkjet proofer that has the specification that says it prints at 2880 x 1440 dpi does not mean that the resolution is finer, or that the droplets of ink are finer in one direction. Instead it simply means that the paper is moved more slowly in one direction - i.e. the addressability is changed - while the physical size of the droplet of ink, and hence its resolution remains the same.
On the left a symmetrical inkjet addressability grid (600 x 600 dpi). On the right the same printer set at 1200 x 600 dpi. The addressability has changed but not the size of the cyan droplet of ink and therefore the actual resolution of the device remains the same.
In any case, the actual size of the mark the droplet of ink makes on the paper is unknown. For a 600 or 1440 "dpi" ink jet printer it most certainly is not 1/600ths or 1/1440th of an inch in size. As a result, with some inkjet printers, reference is sometimes made to "picoliters" in addition to dpi when the resolution of the device is described in the specifications. A picoliter is a unit of fluid volume. A lower minimum ink volume tends to yield a smaller minimum droplet size of ink allowing more dots of ink to be in the same area thereby yielding higher actual resolution. While picoliter is a better indicator of the relative size of the splat of ink on the paper it is still a unit of volume and not area. So it suggests a difference in resolution but doesn't actually specify it.

DPI - when used to describe the resolution of an image scanner. E.g. "This is a 600 x 2400 dpi scanner."
An image scanner—often abbreviated to just scanner—is a device that optically scans images, printed text, handwriting, or an object, and converts it to a digital image. The resolution of Digital images is usually expressed as dots per inch or pixels per inch. As a result the resolution of scanners is often expressed in terms of dpi (and sometimes "ppi" pixels per inch). The more accurate description is "spi" which stands for "samples per inch" since scanners sample the document they are scanning.

A related issue with defining scanner resolution is that manufacturers typically refer to the scanner's interpolated resolution - which is a software upsampling algorithm method to increase the pixel density - instead of using the scanner's true optical resolution. If the scanner's dpi is asymmetrical (e.g. 600 x 2400 dpi) then the smaller number usually indicates the particular number of individual samples that are taken in the space of one linear inch while the larger number is the interpolated samples.

DPI - when used to describe the resolution of an image. E.g. "This is a 300 dpi image."

Once an image has been digitized, either via scanning or captured with a digital camera, it is in the form of a raster image made up of pixels (picture elements). In graphic arts usage the pixels are typically square in shape and 8-bits (256 grey levels) in depth per channel (greyscale = one channel, RGB = three channels, CMYK = four channels).

Because pixels are generally thought of as the smallest single component of a digital image, the more pixels that are used to represent an image, the closer the result can resemble the original.As ppi, a.k.a. "dpi", increases so does the amount of image detail that can be rendered creating the impression of greater apparent resolution.Pixel counts can be expressed as a single number, e.g. an image at 100% reproduction size being 300 "dpi", or as in a "three-megapixel" digital camera, which has a nominal three million pixels, or as a pair of numbers, as in a "640 by 480 display", which has 640 pixels from side to side and 480 from top to bottom (as in a VGA display), and therefore has a total number of 640 × 480 = 307,200 pixels or 0.3 megapixels.
Again, the measures dots per inch (dpi) and pixels per inch (ppi) are sometimes used interchangeably, but have distinct meanings, and although dpi is often used to refer to digital image resolution the proper term is "ppi" - pixels per inch.

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.

Standardize your print process

A standardized print manufacturing process is critical for achieving effective press to proof color alignment, short press makereadies, and minimal wastage of time and materials.


The five basic steps are:

1. Choose the appropriate standard and/or specification target for the presswork.
Management's responsibility (with input from prepress, press room, and sales) is to establish what the targets and tolerances (dot gains, standards, specifications etc.) are for the presswork - because those are marketing/business decisions. Then management must provide the tools to allow prepress and pressroom to achieve those targets. That target then drives the complete print production process and determines the selection of all of the components (proofs, press calibration, inks, paper, etc.) needed to hit the target. Worldwide the most adopted standard for printing is ISO 12647-x. The various ISO 12647 standards provide specifications for data, proofs, inks, paper and press calibration. In North America GRACoL and SWOP specifications are largely based on ISO 12647-2 and ISO 12647-3 respectively.


2. Clearly communicate with print customers about requirements for data/file submission.
This includes items such as whether files should adhere to industry specifications such as SNAP or face rejection. It may include items such as whether native application files are acceptable or only PDFs, what resolution and color mode that images need to be, what minimum text size is acceptable, etc., etc.

3. Implementation of standardized proofing.
In-house proofing must be set up to the same standard and/or specification target for the presswork (i.e. ISO 12647-x, SWOP, etc.). If print customers will be providing proofs for the pressroom then the printer has to communicate that customer-submitted proofs must adhere to the appropriate standard. All proofs must include a color control strip so that they can be verified for conformance to the target standard/specification. There should be virtually no difference in appearance between a customer-supplied proof and one done by the printer in-house. It should also be made clear that the printer's in-house proof is the final proof.

4. Optimize prepress.
The responsibility of prepress is to align proofing to the target established by management as well as to maintain proofing within the tolerances established by management. Prepress must also output plates that enable the press operators to align their presswork to the proofs with the press performing in a repeatable, stable condition. Prepress should have well defined procedures for ensuring that platemaking and the resulting plates are consistent and within tolerance.

5. Optimize press performance.
The responsibility of the press operator(s) is to manage the press in such a way that the the films of the appropriate inks (as defined by the chosen specifications) are laid down in a manner that meets the targets and tolerances (hue, trapping, etc.) established by management and that the halftone dots on the plate are reproduced with fidelity on the various substrates (slur, doubling, etc.). Also, the press operator needs to make sure that all press-related consumables (fountain solution, inks, etc.) are within the tolerances needed to achieve the management defined targets for pressroom output.

Misregistration on press

You may have the most accurate CtP, the best and newest offset press, however, you are still covering absorbent paper with ink and water and squeezing under pressure in the press. The result is that there will always be a chance of misregistration in the presswork.

Here are a few of the most commonly encountered types of misregistration:

Back sheet flare (a.k.a. flare-out or coning)
Back sheet flare usually happens when a lightweight paper is printed with heavy ink coverage. As the sheet is pulled through the press the tail corners of the sheet fan out slightly causing misregister in the corners.
Back stretch
Back stretch can occur if blanket and packing on one or more units may have been compressed during the pressrun, causing change in the print length.
Waggle
Waggle can occur if there's a problem with the on press register system and/or side guides.
Web growth
One type of web growth occurs on web press as the paper streams from ink unit to ink unit. The paper edge gives up moisture at a different rate than the middle of the web. This changes the size of the paper and hence causes misregistration.
Fit
Misregistration occurs when one or more colors do not fit with the others in a set. It is typically caused by the film, or plate in a CtP device, changing size due to environmental temperature changes. As the temperature increases the film/plates expand so the image on plates imaged at different times may be different.
Despite the fact that some degree of misregistration is normal in the printing process, and that it impacts the integrity of the final presswork - as far as I can determine - it's surprising there are no official specifications for what is an acceptable tolerance for misregistration.

In multicolor printing, when all the layers of inks are in perfect register, one is not aware of the individual ink layers, only the image created by their combination.

However, if one or more of the individual ink layers begins to move out of register, the image begins to appear softer, with lower detail definition. Color and tone may subtly shift. And if the ink layers continue to move further out of register, color fringes begin to appear at the edges of detail, and finally the color image breaks up.

There is no absolute point at which the loss of register between the ink layers causes the color or image integrity to become unacceptable. And while misregistration can be expressed in thousandths of an inch or millimeters or in angular degrees, its effect on color register will change depending on several factors. For example, misregistration is most visible in reverse type within a four-color process area. The sharp edges of the type and the high color contrast between the inks and the bare paper exaggerate the visibility of any color fringing caused by misregistration. But color images with little sharp detail or where a black border hides the edges can tolerate a greater degree of misregistration before the reproduction is seen as unacceptable.

Experienced press operators have an intuitive understanding of these factors which has led - in the absence of industry specifications - to a pragmatic approach to the problem of misregistration. The historic, trade practice has been that misregistration is deemed acceptable up to 1/2 row of dots. That is enough to shift a rosette from clear-centered to dot-centered. So, for example, at 133-150 lpi that's about 0.0033ths of an inch (0.0083 cm at 60L/cm).

In register - clear-centered rosettes with a uniform edge.
Out of register by a distance of one half a row of dots - clear-centered become dot-centered rosettes with, in this case, one color layer hanging outside the other three creating a color fringe.
How the press operator measures misregister
Of course, press operators cannot directly measure the amount of misregistration. Instead, when they look closely at the press work through a loupe they employ a simple visual trick:The press operator visualizes the width of a row of halftone dots divided into quarter distances. The solid black lines show the width of one row of halftone dots. The long-dashed black line goes through the center of the dots. The short-dashed lines divide the width of the dot row into quarters. For a 150 lpi halftone, the spacing between adjacent dotted lines is 0.0017" (0.04 mm).
Although trade practice has been to hold misregistration to within one half row of dots - which seems to be a very tight tolerance - there is still a negative impact on the integrity of the press work.

As the dot structure goes from clear-centered to dot-centered as it drifts out of register, the rosette becomes twice as visible effectively halving the screen ruling. So, a dot-centered 150 lpi rosette structure is as visible as a coarse 75 lpi screen. This is often seen like a rash on important skin colors where small amounts of misregistration make the rosette appear then disappear. And as the rosette drifts from clear centered to dot centered it’s like intermittently turning a light on and off and back again - so the color goes intermittently darker and lighter through the run.

Lastly, misregistration changes the overprint ratios of wet and dry trap - causing a color shift. So while the image is going darker and lighter it is also shifting color from bluish to redish and back again. For example, this can be particularly troublesome in, for example, car brochures where there are large expansive areas of neutral grey made up of 4/c process.

A guide to print misregistration - symptoms and causes.

Symptom
If, in a pull of inspection sheets, only one sheet is misregistered out of tolerance.
Cause
Likely no action is needed as the misregister may be just a chance occurrence.

Symptom
If, in a pull of several consecutive inspection sheets, one or more sheets is misregistered out of tolerance.
Cause
Check the press register system and check the paper for wavy edges.

Symptom
Registration is good on several pulls of inspection sheets, but shows a drift toward the limits for misregistration in one or more colors.
Cause
Check the press gripper edge and side-guide register settings.

Symptom
While the gripper edge registration is good, there is a consistent sidewise misregister along trailing edge. The paper may occasionally show wrinkles.
Cause
Check for excessive impression/blanket squeeze which may be stretching the paper. Also check the paper for wavy edges.

Symptom
Misregistration varies from sheet-to-sheet, mostly in the around the press cylinder direction and is worse along the trailing edge of the sheet.
Cause
This usually happens due to mechanical stretch in lightweight papers. It can also happen with loose blankets or it the ink tack is too high.

Symptom
Misregistration appears to be random and occurs in different areas on different sheets within the run.
Cause
This sometimes occurs when printing heavily embossed papers. The impression pressure may need to be reduced.

Symptom
Specific colors are consistently longer or shorter from gripper to trailing edge.
Cause
The blanket and packing on those units may have compressed during the pressrun causing change in print length.

Symptom
Consistent misregistration at the gripper edge or side-guide edge.
Cause
Check the press register system.

Symptom
Random misregister at the gripper edge or side-guide edge.
Cause
Check the paper edge as the trim may be bowed convex or concave or the paper may have wavy edges.
Alternatively the press speed may be too fast for register system to function properly.

Symptom
Misregistration occurs lengthwise along the gripper edge.
Cause
The paper may be grain-short, its moisture content too low, or the pressroom humidity is too high.
Check the side-guide and sheet-forwarding mechanisms.
The plates may have been imaged in different temperature conditions and may need to be reimaged.

Symptom
Registration is good except for a consistent misregister in one area of sheet.
Cause
If the area of misregistration is on off-guide side trailing edge, check paper for wavy edges.
Check the plates as they may have a built-in misfit caused during imaging in which case new plates will need to be made. There may be a large solid on an earlier-down color near the area that's misregistered, causing paper stretch in that area.

What the press operator is scrutinizing

It's the stereotypical image of a press operator - bent over the presswork and examining it under a loupe. People attending a press approval often wonder what the press operator is examining so closely. In fact there's a great deal of information that the press operator can determine from a close up view of the press work.

The first thing that's checked is registration.On the left, dot centered rosettes indicate that the presswork is out of register by one half row of dots. On the right, clear centered rosettes shows the presswork is in register.
Misregistration can also be determined by examining the edge of images to see if one of the process colors is extending beyond the image edge. Click on the above image to enlarge.
Next is halftone dot formation.Halftone dots can reveal issues such as dot doubling that may be the result of loose or incorrect blanket packing.
Here speckles of ink indicate there may be a problem with the plate processor. Also, in this case, the black printer is, because of the elongation of the dots, showing a problem with slurring.
The amount and type of halftone dot distortion can reveal problems with ink water balance as well as the condition of the fountain solution.
When halftone dots are the same size and should be the same approximate density as in the case of Cyan and Magenta - but aren't - this can signal a problem with the solid ink density or an ink/water imbalance.
Pinholes forming inside halftone dots can signal a calcium carbonate issue.

Ghosting

A printing "ghost" is an unwanted image resulting from the printing system itself. There are basically two kinds: mechanical and chemical.

Mechanical ghosts are usually visible as soon as the press sheet lands in the delivery section of the press. There are three types of mechanical ghosts: starvation, blanket, and plate.

Starvation ghosts

A "light print ghost" appears in large solid or dark halftones either as a light or dark image of another part of the press form. It is caused by the layout of the press sheet elements combined with the limitations of the press inking system.Light print starvation ghost.
This can happen when graphic elements contact the form rollers on the press just ahead of large areas of heavy solid ink coverage. The graphic elements remove more ink from the form roller than the press can make up before these rollers come in contact with the solid. As a result the solid receives less ink in those areas and the graphic elements appear as a light image in the solid.

Strategies to avoid this problem include: rotating or "cocking" the press form relative to the press sheet so that the graphic elements are no longer in the same inking zones, changing the imposition or design to eliminate the problem, running the job on a larger press with greater inking capacity, making sure that water levels are run at a minimum, running on a larger press sheet and adding "take-off" bars - graphic elements - in the non-live image area of the sheet to even out ink usage.

A "dark print ghost" occurs when knocked out graphic elements immediately precede an area of heavy ink coverage.Dark print starvation ghost.
This is the opposite of a light print ghost. Here, the knock out can cause excess ink to remain on rollers in the reverses causing a dark image of the graphic to appear in the large solid.

The same strategies used to avoid a light print ghost are also used to avoid a dark print ghost.

A "plate ghost" or a "blanket ghost" appears when graphic elements intrude into the printing as latent images.Plate/blanket ghost.
This problem usually occurs on multicolor presses where the press form on one of the color units sensitizes the plate of the following color unit. Proper desensitizing of the affected plate and ink adjustments should correct the problem, however, sometimes the plate and/or blanket may need to be replaced.

Comment below submitted by "Otherthoughts"

For what it's worth? The how, why and when that I've used ink take-off bars in the past.

Solid ink Borders were the most prone to a starvation type of mechanical (ghosting?) in my experience, especially PMS spot color borders.

In my sheetfed experience, often there was a bit of space available for ink take-off bars, our standard sheet size was 19" x 25". Despite there being some space available, ink take-off bars were never used to make a job easier running and nicer looking as a matter of course by anyone other than myself. I employed them as a stripper because I knew that the pressman would appreciate the help (being a former pressman myself), and because I knew it would produce a better printed result.

The type of job that really needs them, doesn't come along all that often, here's an example.

Lets say the form below shows a reflex blue to be run as a fifth color. And lets say that the reflex blue borders will trim out to be 1/2" wide on all four edges.Without ink take-off bars, ink usage ranges from 17.125" to 2.125", a ratio of 8 to 1
With ink take-off bars, ink usage ranges from 17.125" to 3.562", a ratio of 4.8 to 1

Layout Details
Limited the bleed at both the gripper and tail to 1/16" each. Butted the pages together at the circumferential center line mark and finally shrunk the Color-bar down to 1/8". This leaves 1 7/16" to implement the take-off bars on a 19" x 25" sheet.

Gripper margin = 00.312
8.5 x 11 x 2 = 17.000
Bleeds x 2 = 00.125
Color bar = 00.125
Total = 17.562

Notes As you well know, ink take-off bars are useful with low total ink coverage scenarios as well, but such scenarios have nothing to do with ghosting/starvation. Regardless, prepress failed to employ ink take-off bars in this scenario just as well. If there was no room for ink take-off bars on a job, we did without them, which was essentially "No Change" from what we did in all cases. :)

Gordo's response

The iconic National Geographic magazine cover border is a great example of this problem - but uses a different solution. They don't have enough space on the press form to add ink take-off bars, so instead, in anticipation of the increase in darkness at the top and bottom of the picture window, they use a screen tint of the solid spot color in those sections of the border.Left: as the cover would print with a solid spot yellow border. Right: as the cover prints with the top and bottom sections of the spot yellow halftone screened.
The screened part of the spot yellow bar gets darker on press due to the mechanical ghosting effect and ends up the same color as the solid yellow on either side.

Chemical ghosts are related to the chemical activity of inks as they go through their normal drying process. Their appearance is usually unpredictable and, unfortunately, become evident only after the job has been printed and in the press delivery pile for a period of time.

Chemical ghosts may appear as reproductions of one side, or part of a press form, in the solid area of another part. Their appearance can be erratic - showing up in one area of the printed sheet but not in a similar or duplicate part. They usually appear as a dull ghost on a glossy background or as a glossy ghost on a duller background.

What makes an ink glossy or dull.

When an ink appears glossy, it is the result of enough ink vehicle forming a film on the surface of the paper to provide a smooth covering layer for the pigment particles in the ink.Graphic representation of the edge of a sheet of paper showing ink pigment particles suspended in the ink vehicle.
When an ink appears dull, it is the result of the ink vehicle draining from the surface into the paper so that the irregularities of the individual pigment particles and paper surface are not covered with a thick enough film of ink vehicle to create a gloss appearance.

How inks dry

When ink is printed on a press it goes through two distinct phases:

1 - Setting - the drainage and leveling of the ink vehicle into the paper coating or fibers. This causes the ink to "gel" and become immobilized.

2 - Oxidation - the polymerization of the ink vehicle into a solid mass creating a hard film.

As the film of ink oxidizes it releases gaseous by-products. As a result, the ink printed on the second side of the press sheet can be exposed to the gaseous by-products from the oxidation of the first side if it is printed at a critical point in the first side's ink drying cycle. Those gasses affect the drying rate of the second side ink selectively as the sheets are stacked in the press's delivery. This results in an ink film that has been immobilized at two very different rates, and therefore has areas of high or low gloss which reflect the image on the other side.Graphic representation of sheets of paper in the delivery of the press showing gaseous by-products released as the ink dries.

Rich black - the problem of black in presswork

Like all process color inks, the black ink that is used in 4/C printing is transparent. As such it cannot cover ink, or black out the paper, as thoroughly as one might hope. Instead, black ink by itself actually appears to the eye as ranging from an apparent black when it's used to cover very small areas to just a dark grey when it covers large areas.Even though it appears greyer, the box on the right is the same printed 100% black as the text on the right.
The solution to the problem of grey blacks is to boost blackness by printing other inks under the black ink. This effectively darkens the brightness of the paper over which the black ink will be applied thus making the black "blacker."

Blacker black strategies

There are several ways to making a black blacker:

1) Apply a screen tint of a process color - magenta or cyan down before the black.

2) Apply a mix of process colors - cyan, magenta, and yellow down before the black.

3) Apply two hits of black ink.

The first option is sometimes called a "rich" black, while the second is called a "super" black, and the third a "double black."

With a Rich black the other process ink is usually a 60% tone of cyan. This causes the black to appear “blacker” because the second ink color increases its density. It also makes the black "bluer" which adds to the darker appearance. A 60% magenta could be used instead of cyan to impart a warmer appearing black.Left: 100K/60M. Center: 100K. Right: 100K/60C.
Rich blacks are typically used whenever the image is larger than 1 square inch and smaller than about 9 square inches in area.

A Super black, where 3 process colors underlie the black, is typically used when the black area is larger than about 9 square inches in area. The typical screen percentages are: 50% cyan, 40% magenta, 40% yellow, and 100% black.Left: 100K. Right: 100K/50C/40M/40Y.
In contrast to using a single process color, this screen tint combination preserves the neutral appearance of the black. This screen ink combination also means that the maximum amount of ink in the black amounts to just 230% coverage which should not cause any on-press issues like excessive drying times.

Unfortunately a Super black can be problematic on press because it is used for large black areas while at the same time using the same inks that are used for the color-critical image areas. That can cause a conflict on press if ink densities need to be adjusted to align the image colors with the proof while keeping the Super black neutral and at the correct density. To solve that problem, printers may opt to use two hits of black ink. The first black ink is tied to the CMY of the images, while the second black is independent of the image. That allows the press operator to adjust the CMYK inks as necessary to get good color on the images with the second black ink only being applied where a large area of black is needed. The downside to this strategy is that it turns a 4/C job into a 5/C job (CMYKK) which may increase production costs.

The black booby trap

On a computer monitor, there is only one way to represent black - the screen is black when there is no light coming from the display. So a 100% black, a Rich black, a Super black, and two hits of black will all appear the same on screen.A 100% black bar, a Rich black bar, a Super black or, two hits of black ink all appear the same on screen.
100% black bar as it appears in print if it is set to "knock out" of the background image.
100% black bar as it appears in print if it is set to overprint the background image.
A Rich black bar - 100%K/60C as it appears in print. The 60% C not only serves to darken the black but it also knocks out the background image which eliminates any "ghost" images caused when black simply overprints a background image.
Because the on-screen appearance of the black may appear the same despite being made up of different screen tint combinations it is critical that the Rich, or Super black be clearly identified as such in the custom color menus of page layout and illustration applications. Create the color and name it according to its function and make up. E.g. Black for standard process black, "RichBlack 100K60C" and "SuperBlack 100K50C40M40Y"

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.

A billion dollar printing fiasco - U.S. $100 bills made worthless by a "printing" error.

Was it a failure of basic print quality control?

The U.S. Federal Bureau of Engraving and Printing has identified a problem in the new security enhanced $100 note. Apparently the notes have blank patches caused by "sporadic creasing of the paper" which were discovered only after the printing was completed.The Bureau's current visual print quality control system may be inadequate for the demands of this new level of security printing.
1.1 billion of the new bills have been printed but officials don’t know exactly how many of those bills are flawed. There is, however, speculation that as many as 30% of the bills are affected. It's estimated by officials that sorting the bills by hand could take 20-30 years. While sorting using a mechanized system may cut the time down to just one year.

Fed officials are working with staff from Crane and Co, suppliers to the US government of currency paper since 1879, to solve the problem. Crane and Co. have denied that the paper they supplied is the cause of the Fed's troubles.

Although the Bureau is now looking into automated inspection to find the defective bills, it does seem strange that, apparently, they don't already use an automated inline full press sheet inspection system.


Printing, inspecting, and packaging of defective $100 bills at the U.S. Federal Bureau of Engraving and Printing.
This problem means that the Federal Reserve will not have sufficient inventories to begin distributing the new $100 notes as planned and will instead be printing more of the old style bills in order to meet demand. One only hopes that the Fed will implement more stringent quality controls when reprinting the old style notes.The old style bills will be pressed back into service until the defective new bills are found and destroyed.
"I didn't fail the test, I just found 100 ways to do it wrong."
Benjamin Franklin - whose portrait graces the $100 bill was one of the Founding Fathers of the United States and a noted author, inventor, and most importantly a printer.