The eternal conflict - ink/water balance - the tale of the tones

An AM/XM halftone screen has a builty-in conflicting ink/water balance requirement on press. The highlight dot and quarter tone range from 1-35% requires minimal water and maximum ink in order to prevent those dots from being washed away. The three-quarter tone range from 65-99% requires the opposite - a larger volume of water in order to prevent the shadow dots from filling in and disappearing. On the other hand, the mid-tone range from 35-65% is more of a balance between ink and water.

Halftone dots and the tones range they represent are affected differently by the condition of the ink on press - assuming of course, that the plate, press, and chemistry are set up correctly. Unfortunately, if the press operator attempts to fix tone reproduction in some areas, that built-in difference in ink/water requirement can exaggerate the inherent conflict and cause problems in other parts of the tone range.

1 - 1-35% This tone range is primarily affected by the body/viscosity of the ink. If the body is too soft the highlight area will print too full which may cause the press operator to decrease solid ink density in order to reduce the dot size. Alternatively the fountain solution may over-emulsify this tone range causing poor ink transfer and loss of highlight detail. If the ink body is too heavy the dot may print too sharp causing the press operator to increase the density or blanket pressure.

2 - 35-65% This tone range is primarily affected by the strength (pigment load) of the ink. If the ink is too weak the press operator will increase solid ink density which will cause increased dot gain and result in presswork that appears too full. If the ink is too strong the midtones may print too light. Also, the strength of the ink also impacts how well the inks trap, which in turn affects the color gamut the press should be able to achieve. Varying the strength and stiffness of the ink to achieve good tone reproduction in presswork is a method press operators, who don't have good communication with prepress, often employ. It's almost always better to use tone reproduction curves applied in plate imaging than to modify inks.

3 - 65-95% This tone range is most strongly affected by mechanically induced dot gain or chemistry issues i.e. (poor ink water balance). If the tone range from 1-65% is evenly balanced then excessive gain in the shadow tones is usually caused by running excessive water, too much blanket pressure, and/or mechanical slur.

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.

Slur

Slur is often confused with doubling as their initial appearance is very similar. However slur is invariably an elongation of the dots in the sheet travel direction. The usual cause of slur is either over or under cylinder packing. Loose blankets, too much plate-to-blanket pressure, too much ink on coated paper, and ink rollers set too hard will also cause slur.

Doubling

Doubling is often confused with slur as both exhibit an elongation of halftone dots. However, slur is usually an elongation in the direction of sheet travel through the press while doubling can be in any direction. Doubling (and slur) often manifest as a problem with the range of tones available in the presswork being compressed and loss of detail, particularly in the shadow areas (a.k.a. muddy halftones). Doubling can be caused by many of the same factors as slur. When the cylinders rotate the halftone dots are not placed in exactly the same position with every revolution. As a result the dots print up as double or multiple images. Doubling between units occurs when a blanket picks up a previously printed ink film. This is known as backtrapping. Examine the dots, or line art graphics, under a loupe to confirm whether the problem is doubling or slur.

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.

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"

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.

To linearize your CtP plates or not?

A bit of background
Back in the old film to plate days the standard prepress procedure was to linearize film output. That means a specific tone request in the original file results in halftone dot in the film equal to the file tone request. So, for example, a 50% in the file became a 50% tone in the film. Linear film was the agreed standard interchange file format between prepress tradeshops, publishers and printers. At that time, the final tone on the plate was not measured. Instead, the resulting tone in the presswork was measured and deemed to be in specification, or not, relative to the supplied linear film. I.e. At 133 lpi, a 50% tone in the film resulting in a final tone of about 71% in the presswork would be considered in specification. Interestingly, although the film was linear, the resulting plates were not linear due to the dynamics of exposure in the vacuum frame.

The arrival of CtP in the late 1990s eliminated film as the intermediary. As a result, measuring tone values on the plate became a process control metric. However, CtP plates seldom have a linear response to laser exposure and if a tone reproduction curve is applied to them to make them linear - the resulting presswork is usually too "sharp" - i.e. not achieving enough dot gain.

At the same time that CtP was rapidly being adopted, printers also began to use finer halftone screens, including FM screens, which had very different dot gain characteristics compared to the old published standards. Printers began to leverage the flexibility that CtP provided in being able to apply different tone reproduction curves to their CtP plates to achieve the tone reproduction on press that they required.

So the question for the printer becomes: should prepress first apply a curve to linearize the plate and then, if needed, apply another curve on top of the first to achieve the desired final press tone response?

I was shocked
So, just to confirm that the method that I have been using for the past 13 years was indeed the standard method used in the industry, I posed the question to an internet printer's forum: "Do you linearize your plates before applying a press curve (a two curve workflow - e.g. one to linearize the plate followed by another one to compensate for dot gain) or do you only apply a press curve to the uncalibrated plate (a one curve workflow - e.g. one to compensate for dot gain)?"

The response shocked me - a whopping 70% said they first linearized the plate with a curve and then applied a press curve while only 30% responded that they simply applied a press curve to the uncalibrated (natural state) plate.

70% using one curve on top of another? That makes no sense to me at all.

In a film to plate workflow, linear film is exposed to the plate in a vacuum frame. The function of the plate exposure is to reproduce the halftone dots in the film as consistently as possible across the surface of the plate, and perhaps more importantly, to create a robust halftone dot on the plate that will maintain its integrity on press. However, although the film may be linear, the resulting plates are not linear due to the dynamics of exposure in the vacuum frame. In North America using negative film there is typically a 2%-5% dot gain on plate at 50% (i.e. 50% in the film creates about a 54% on the plate) while in Europe and Asia where positive film was used there is typically be a 2%-5% tone loss at 50%.

In a CtP workflow, as with a film to plate workflow, the important thing is to set laser exposure and processing (or lack thereof) to the manufacturer's specifications so that the result is a robust halftone dot on the plate that maintains its integrity on press. However, as with a film workflow, the resulting plates are typically not linear due to the dynamics of laser exposure, individual plate characteristics, and processing.

In this example, the thick line that dips below the 0 line is the natural uncalibrated plate curve after the engineer has done their work setting up exposure and processing for the most robust dot possible.With this particular positive thermal plate the uncalibrated plate curve results in a negative value through the tones. The bottom numbers in the graphic are the requested tone values in the file - 5%, 10%, 20%.... 90%, 100%. The "0" line represents linearity. I.e. if the plate was linear then that 0 line would be straight and be the "plate curve". But, in this case, a 50% request has resulted in about a 47% on plate. This is fairly typical - a well and properly exposed CtP plate does not have a linear response (i.e. a straight line). Also note that it is typically not a classic Bell curve - there is no symmetry. Different CtP/plate combinations will each have their own characteristic natural curves.

So, from a CtP vendor engineer's perspective, it does not matter whether the result of their setup is a linear plate or not since a tone reproduction curve can always be applied to achieve whatever tones are required on plate - including linearizing the plate. What's important is that the exposed dot is robust and that the plate imaging is consistent across the plate and repeatable from plate to plate.Put another way - the key criteria is that when properly set up the plate will have a characteristic non-linear tone response. And that's fine - as long as the plate responds the same - i.e. delivers the same non-linear tone response – every time because without that consistency it is not possible to build any tone reproduction curves at all.

Some definitions

These definitions are not "official" however they are useful to keeping the issues and discussions clear.

A "plate curve" is a tone reproduction curve that is applied in the workflow to a plate in order to have it render tone values that are different from those it delivers when the laser exposure and processing (or lack thereof) have been set to the manufacturer's specifications. So, applying a linearizing curve that makes an inherently non-linear plate linear is an example of the use of a plate curve.

A "press curve" is a tone reproduction curve that is applied in the workflow to a plate in order to have it render tone values that are required to deliver a specific tone response on press. The assumption is that the laser exposure and processing (or lack thereof) have been set to the manufacturer's specifications.

By this definition, if only a linearizing curve is applied because a linear plate is needed to deliver the correct tone response on press then that linearizing curve is a press curve.

A plate curve in this sense is not related to tone reproduction on press. It is effectively a calibration curve. It brings the plate to a known condition. However, in a CtP environment, the manufacturer's setup of laser exposure intensity, processing chemistry, and processing time effectively calibrates the plate plate to a known condition. It might not be linear but it is known. There is no need to recalibrate by applying a plate curve to what is already calibrated.

Another way to look at the question

Let's suppose that a linear plate provided the tone response on press that we need. Would it make sense to then use two curves - one to linearize the plate (a plate curve) and a second curve (a press curve) to linearize the linearized plate? I doubt it. Makes more sense to just apply the one linearizing curve - based on the uncalibrated natural condition of the plate.

So, if that logic makes sense, why wouldn't it make equal sense if we needed a non-linear press curve? Just apply the one non-linear press curve based on the uncalibrated natural non-linear condition of the plate.

As long as the plate's tone response is consistent then it can be the basis on which to build press curves. However, if the plate is inconsistent in its tone response then the use of linearizing plate curves as well as the use of press curves will fail. You cannot use curves, plate or press, on a device that is inconsistent.

What the "authorities" have said*Some quotes on this topic from the Idealliance G7 guides:

6.2 Origin of NPDC curves
To determine the 'natural' NPDC curves of commercial CtP-based printing, G7 research analyzed numerous press runs made with ISO-standard ink and paper, and a variety of plate types imaged on “un-calibrated” CtP systems (no RIP curves applied, not even to “linearize” the plate).

5.4 Set up the RIP
Set up the plate making RIP exactly as you would for a normal job, but clear out any values in the current calibration table, or begin with a new, empty table. The first press run is best made with ‘un-calibrated’ plates – i.e. no calibration values in the RIP.
IMPORTANT: Do NOT linearize the plate-setter so that measured dot values on plate exactly match original file percentages. Contrary to common belief, this may reduce accuracy of subsequent steps.

a. PRINTING IDEALIZED TARGETS VALUES - Achieving calibration condition with raw or linear plates, not requiring a curve, is an ideal situation.

*A note about authorities. I had trepidations about including these points from G7 because I do not believe that people should blindly do what some authority says they should do. It is not enough to say "Do it this way because I say it should be done this way." If the authority cannot explain exactly why one way is wrong and another right then it is just an opinion and without evidence to back it up it is not a credible opinion. I included these quotes only because they may carry credibility for some readers of this post.

Scenarios“We’ve always done it this way!” or “This way works just fine!” Even when we have the time to think about how or why we do things a certain way, our thoughts are often clouded by that kind of thinking. However, it can make it easier to understand the merits of a one curve workflow compared with a two curve workflow if one breaks down the sequence of steps required to get a plate into the press room. Given the same final result, the fewer the steps - the better the workflow since it provides fewer opportunities for error.

Here are some examples of workflow scenarios to see what happens with a one curve workflow vs a two curve workflow:

One CtP & one plate shop - to achieve the same final result on press:
One curve workflow: one press curve = one curve total.
Two curve workflow: one linearization plate curve plus one press curve = two curves total.

One CtP & one plate shop using three different curves to optimize for three different papers. To achieve the same final result on press:
One curve workflow: one press curve per paper type = three curves total.
Two curve workflow: one linearization plate curve plus one press curve per paper type = four curves total.

One CtP & two plate shop - to achieve the same final result on press:
One curve workflow: one press curve per plate type = two curves total.
Two curve workflow: two linearization plate curves plus one press curve = three curves total.

One CtP & two press shop - to achieve the same final result on two presses:
One curve workflow: one press curve per press = two curves total.
Two curve workflow: one linearization plate curve plus two press curves = three curves total.

One CtP & one plate shop - what happens if a new batch of plates do not perform as the previous batch did:
One curve workflow: modify one press curve so that the plate tones are the same as the previous plate batch = one modified curve total.
Two curve workflow: modify one linearization plate curve plus apply the standard press curve so that the final plate tones are the same as the previous plate batch = two curves total.

One CtP & one plate shop - what happens if the press curve needs to be tweaked/adjusted:
One curve workflow: modify one press curve to achieve the required tone reproduction on press = one modified curve total.
Two curve workflow: one linearization plate curve plus modify one press curve to achieve the required tone reproduction on press = two curves total.

One CtP & one plate shop - what happens if the CtP device is replaced:
One curve workflow: measure the new plate output and modify one press curve to achieve the same tone reproduction/dots on plate as with previous CtP = one modified curve total.
Two curve workflow: measure the new plate output and modify the linearization plate curve to linearize the plate then apply the existing press curve = one modified curve for two curves total.

Looked at this way, the linearization plate curve, in the vast majority of cases, is redundant. It serves no useful purpose except to add complexity and another point of failure.

Every letter tells a story - print problems revealed in type reproduction.

Spend even a small amount of time in a printshop and you'll quickly realize how much effort press operators put into scrutinizing their presswork through a loupe. The two things they're typically looking for are clear centered rosettes - this tells them that the presswork is in register – and print problems revealed by how well individual letters of type are reproduced in print.

Here's how type printed offset reveals problems:

Normal ink transfer - no apparent problems.


Doubling
A ghost image appears just behind the primary graphic causing an increase in dot gain. More information about doubling HERE

Slur
A smeared ghost image appears just behind the primary graphic. More information about slur HERE

Over emulsified (a.k.a. emulsified, water logged)
Ink is designed to accept a small amount of water (fountain solution) on press. Too much water appears as tiny droplets in solid areas and reduces gamut, image sharpness, contrast, and increases dot gain.

Tailing (a.k.a. misting, slinging)
Too high a solid ink density or ink that's too "long" can cause thin "tails" of ink strands to appear extending behind the primary image causing a loss of sharpness, contrast and an increase in dot gain.

Picking (a.k.a. pinholing)
Small white specks appear in solids. This usually results because the ink tack is too high or there is not enough impression cylinder pressure ("squeeze").

Ink breakdown
On press, fountain solution acts like a solvent. If it is too aggressive or acidic it can break down the ink that forms the image resulting in presswork that appears muddy and/or "soft." It also reduces total gamut because it reduces overprint trapping efficiency.

How was it printed? Simple ways to determine the printing method used.

The proliferation of new printing technologies like commercial production toner and ink jet presses as well as the rapid increase in quality of some traditional systems like flexography, has made it a bit difficult to determine exactly which printing method was used for a given sample. Was it offset or digital ink jet? Flexo or offset?

Here is a guide to help you identify which printing method has been used. The best method is to look very closely with a loupe at the letter forms and then confirm by looking at the halftone dots themselves. Although these images were taken at about 200x to show as much detail as possible, they are not that different than what would be seen by the human eye under a loupe at 10-20x.

Offset lithography

Type edges are sharp and well defined. The ink density is similar across the letter. The paper around the printed ink is usually clear/unprinted. The sharpness and consistent ink density is reflected in the halftone dots. Note that this same sharp appearance occurs if the halftone screen used is FM (the third image) rather than AM (second image).
Gravure

All graphic elements appear halftone screened so the edges of text show a rough halftone appearance. Although presswork color may appear rich, viewed under a loupe, the halftone dots may have a watery appearance. Individual dots may appear to have a hole in their centers.
Flexography

Flexography uses a rubber-like plate that, under pressure, transfers ink to the substrate. This results in type that often appear to be surrounded by a sharp-edged "halo." The same effect, but in opposite, occurs in the halftone dots which may have dark edges and light centers. Both type and halftone dots usually have very sharp and well defined edges. Note that this dot sharpness also occurs with an FM screen printed with flexo (third image).
Electrophotographic (a.k.a. laser toner, Xerographic)

With electrophotographic systems the image is created by depositing a powder toner. This results in a "sprayed on" appearance. Type edges are soft and there are often specks of wayward toner on what should be unprinted paper. On close examination you'll likely see apparently random Yellow dots. Those are anti-counterfeiting tags. Halftone dots have a similar fuzzy appearance.
Inkjet

Under a loupe, ink jet type has a "blocky" "chunky" edge appearance. This is caused by the low resolution/large droplet size typical of these devices (despite the claims of high dpi). Sometimes there will be the occasional "satellite" ink droplet near the letter (two are shown in the image below). Because of the way the ink is sprayed onto the substrate, halftoned areas appear to be done with an FM screen. However, unlike the FM screening used in offset lithography, there is usually no apparent pattern or organization to the dots.
Engraving

Engraving is typically used for currency/bank note printing, stamps, and sometimes very exclusive stationary. Type is very crisp and sharp. The process is capable of extremely fine detail and as a result is used to print security microtype. Halftones are usually created with line effects rather than a conventional halftone screen. Softly passing one's fingers over the printed work will reveal a tangible texture due to the raised ink.
Thermography

Thermography is commonly used on wedding invitations, letterheads, business cards, and greetings cards as an attractive alternative to the more expensive engraving process. Type has a raised surface texture similar to engraving however, with thermography type appears to be printed under a transparent coating. The low resolution of this process makes it unsuitable for quality halftone screening.
LCD display (print to screen - just for fun)

The letter "e" as displayed black against a white background on my laptop's display. Since the LCD display produces no light of its own, it requires a cold cathode fluorescent lamp situated behind the LCD panel. Electronically-modulated pixels filled with liquid crystals are arrayed in front of the light source to produce images in color. Passing the backlight through the red, green, and blue liquid crystals recreates the backlight white, while blocking the backlight creates black. Anti-aliasing of the letter helps to smooth the shape of the letter form and compensates for the relatively low resolution of the screen itself. Note that the pixels forming the image are not square but rectangles.