Tolerancing color in presswork by eye

Once the press operator has achieved their solid ink density targets during make ready, they typically will do a visual examination to compare presswork color to proof to evaluate the closeness of the match. They will also do visual comparisons during the run to check the consistency of the match through the press run. Print buyers typically also do the same thing - relying on their eye for color to verify the match and consistency.
For most people in the graphic arts, the eye is the final arbitrator on the quality and consistency of presswork - however, this method has some limitations caused by the fact that the eye is part of a very tricky instrument: the human brain. For example, look carefully at this graphic containing light green and light blue swirls:
Light green and light blue?

Actually there are no light blue swirls, What you see as light blue is actually the same color as the green ones. They are both R 0, G 255, B 151. Cutting out a section of the "light blue" swirls and lining them up with the light green ones proves they are indeed the same color.This illusion is so strong that you might have to down load the image into PhotoShop and confirm it for yourself.

There are several characteristics of our eye/brains that can play tricks on our perception. Being aware of them will help you more clearly understand how your color perception can be mislead and hopefully provide a clearer view as to what you are actually seeing.

1) The eye/brain auto-white balances. The eye/brain selects an area that it "knows" is white - forces it to appear white and balances other colors accordingly. This is the trick that allows us to see a white paper as white with surrounding colors being natural under a variety of different colored lighting situations. This often causes problems with monitor proofs where an image should be "white" i.e. should result in no halftone dots in the presswork, but in fact has grey or even a color cast in it that results in dots being printed. The eye/brain sees the area as white when in fact it is not.

2) The eye/brain has no color memory. Not only does the eye/brain auto-white balance, it also rebalances color whenever you look from one object to another. This makes comparing two colors that are separated, by even a small distance, impossible. For example, in the below image, the press operator cannot effectively compare color between the image on his soft-proof with the color on his press sheet.
The only way to compare two colors is by cutting through one sample and overlaying it on a reference (e.g. cut press sheet over proof) like this:If the color aligns across the cut then you have a match.

3) The eye/brain cannot judge variation consistently. In order to tolerance acceptable color variation, for example custom/brand colors, you need to have a reference high/low density guide that provides an example of the two extremes that the color must fall within. Providing a swatch guide with holes through it as in this example:allows users to place the swatch over the press sheet to more easily confirm the color match as well as whether it falls between the two acceptable extremes.

4) The eye/brain's perception of color is influenced by the size of the area of color. This is one of the reasons that the paint color selected from a small paint chip seldom appears the same as the color once it's painted on the wall. The same issue happens when selecting a spot or brand color from a swatchbook. Always try to get a reference chip, draw down, or previously printed sample, that is as large as possible.

5) The eye/brain's perception of color difference is not uniform for all colors. It is difficult for the eye/brain to see differences in highly saturated colors. However, a small degree of variation is easily seen when colors are near neutral. Variations in the green part of the spectrum are more easily noticed than the same degree of variation in the red part of the spectrum.

The Wayback View - Print Ephemera

"Ephemera: transitory, transient, fleeting, passing, short-lived, momentary, brief, short; temporary, impermanent."

Just a very few examples of print ephemera - items that usually do not survive the passage of time. Rare because, being of little apparent value, very few care to preserve them.

A lenticular letter opener promotes this 1950s printer:
Printer invoices are some of the least preserved aspects of print.

From 1894:
From 1905:
From 1913. Note the two hours of customer alterations resulting in a $1.50 extra charge. Also, the invoice was made just after Christmas and was paid just over thirty days later. Impressive! The fact that this printer is still in business - outstanding!
From 1929:
From 1933. Think short run printing is the latest thing? This invoice to the Catholic Records Society from John Whitehead & Son Limited is for just 25 leaflets.
Print sales representative business cards are also quite rare.

From the 1870s - what a great address: "Between High and Purchase Streets." Partner Clifford displays his complete first name but partner Crawford is only allowed an enigmatic "W." And their unique capability? "First-Class Blank Books a Speciality." In other words, their best printing is no printing at all!
A more conventional business card from the turn of the century:

Even vendor material, although often inspirational, was not likely to be preserved:
If you have any examples of print ephemera to share please send them to me via pritchardgordon (@) gmail (dot) com

Tolerancing color in presswork using solid ink density

Background information - ink film thickness & solid ink density

Offset printing presses are designed to lay down a film of ink, in the presence of water, onto a substrate - usually paper. The ink forms the image while the "water," more accurately fountain solution," prevents the non-image area on the printing plate from accepting ink. For the process to work, there needs to be a critical ink/water balance with the goal of having an ink film thickness between one micron.

If the ink film thickness is too great, the result can be "ink tailing/misting." In addition, the non-image background may take on ink resulting in "catch-up" (sometimes mistaken for "scumming"):
On the other hand, if the ink film thickness is too thin, the result can be a breakdown of the ink on the sheet causing low contrast, loss of sharpness, and mottle:
So, from a color tolerancing point of view, because the function of ink is to filter light and allow us to see color and because its thickness also effects the integrity of the printing process - ink film thickness on the sheet becomes an important metric to measure and tolerance in presswork.Top: CMYK at high ink film thickness/solid ink density.
Bottom: CMYK at low ink film thickness/solid ink density.
There is no practical way to directly measure the ink film thickness on a press sheet. However, there is an indirect way and that is to measure the solid ink density (SID) using an instrument called a densitometer.

Color tolerancing through densitometry

Measuring SIDs in the solid ink patches in the color bar with a densitometer does not actually provide information about the color being printed. However, because it indirectly provides information about ink film thickness (which impacts color and tone reproduction) SID values are valuable for process control and defining variation during a press run where the instrument, ink, and substrate remain the same.North American (Status-T) high-low specifications for acceptable SID variations measured with ink dry.
Top: Commercial sheetfed, Middle: Magazine/heatset web,
Bottom: Newsprint/coldset web.
From a color point of view, the assumption is that all three chromatic colors vary in the same direction and therefore remain in relative balance. When that happens there is a shift in color saturation (higher SIDs = higher saturation) as well as tone reproduction (higher SIDs = higher dot gain/TVI). If one color, e.g. Cyan, is at the maximum low point while another color, e.g. Magenta, is at the maximum high then the result may be a visible color bias in the presswork.
Typical SID variation in presswork graphed by measuring color bar patches every 10 sheets through the press run.
While a densitometer can also be used to monitor variations in non-process, i.e. spot/Pantone colors, usually a printed sample of the target color, including a high/low density tolerance reference, is used instead since this helps both print specifier and supplier visualize the acceptable range of color change as SIDs naturally vary during the press run.Checking for spot color variation
Addendum: Densitometer set up - "Status" condition

Densitometers are set by their manufacturers to an industry defined "Status" which defines the total response of the instrument including light source, optics, filtering, and receptor for given wavelength. The primary responses for the print business are "Status E" and "Status T" (ANSI PH2.18 and DIN 16536). In addition, densitometers are available with or without polarizing filters. Dry ink density readings from polarizing and unpolarized densitometers as well as those set to Status E vs Status T will not agree. Typically European instruments are set to Status E and use polarizing filters while North American instruments are set to Status T and do not use polarizing filters.

The important thing to be aware of is that if SID information is shared outside of the printshop - then the Status of the instruments that were used to determine SID values must be known. In addition, it is critical that all instruments within the printshop are set to the same Status. In North America, where many of the presses and their closed-loop color control systems are from Europe, it is not unusual to find the press set to Status E polarized while the handhelds are set to Status T unpolarized which can easily result in quite a bit of confusion in production.

The future of publishing

This video was prepared by the UK branch of Dorling Kindersley Books and produced by Khaki Films (more info HERE). Originally meant solely for a DK sales conference, the video was such a hit internally that it is now being shared externally. It begins with the stereotype and then...

Click play arrow (and maybe wiggle the play head), to view the video.
You can read an interview with the creator of the video on the Penguin Blog: HERE

RE:Print - "Getting Lean"

The Wayback View – March 1985, Apple introduces LaserWriter

Twenty five years ago, in February 1985, Linotype and Apple announced a joint agreement enabling the Macintosh to send text and graphics to a laser typesetter. The next month (March) Apple shipped its first $7,000 300 dpi office LaserWriter. It was driven by a new language called "PostScript" that had been developed by a small, relatively unknown company called Adobe Systems Inc.

The revolution had begun. However, not everyone was convinced as the challenge in this newspaper article reveals.

Click on image to enlarge
Betty Handly, was probably not aware of the inventive ways that people were already starting to use the Mac and LaserWriter combination for. As just one example, I had set up the prepress production department for a 28 page weekly newspaper "Prince Rupert This Week" by using a combination of Manhattan Graphics Inc.'s Ready, Set, Go! page layout program (later acquired by Letraset), Cricket Draw to handle the special graphics, and an Apple LaserWriter to generate the camera-ready artwork.Using the LaserWriter output for camera-ready art meant that the type smoothed out enough to eliminate the low resolution "jaggies." It also meant that the publisher did not have to purchase the significantly more expensive traditional option of a Linotype machine or a laser filmsetter.

In fact, if it wasn't for the introduction of the Mac and LaserWriter combination, the newspaper would never have been financially feasible to publish in the first place.

Betty Handly went on to create a typesetting business, the 'Type Gallery' which subsequently failed and went into bankruptcy in October 1992. In November 1992 she became involved in a new typesetting business called Centerpoint Prepress, Inc. - a typesetting business which also ran into financial difficulties and ceased operations. Betty Handly managed the company's business activities and was paid $16.50 per hour for her services.

The International Typographical Union has not fared much better as a result of the general elimination of the typographers' trade due to automation, computers and mechanization. The remnants of the union membership are in the Communications Workers of America and the International Brotherhood of Teamsters.

Conducting The Press Check

Printing is a completely different imaging process than proofing. As a result, it is not always possible for the presswork to perfectly "match" the proof. Unfortunately, there is no objective, practical, way of defining what is an acceptable variation from the proof that still constitutes an acceptable pressrun. The role of the press check is to enable the customer, or their representative, to directly communicate their presswork concerns and acceptance, with the press operator, so that a successful pressrun can be achieved.

The customer should be able to go to the press and speak to the press operator directly. Working through an intermediary like the pressroom manager only slows down the process and causes communication errors especially when if they are managing multiple press checks at the same time.

Press check basics for the printer

• The customer should not be press side during initial make ready. Ideally you would have a comfortable holding area/lounge where customers can wait until the press operator has a sheet ready for inspection.

• An initial make ready sheet marked clearly "For Content Only" could be given to the customer so that they can check the sheet for content issues like substituted fonts, low resolution images, missing graphics, etc. This reduces time wasted at the press when doing the color approval. Also, if content errors are discovered then the job can be halted soon enough to avoid excessive make ready wastage.

• The press operator should be told ahead of time, by the CSR or sales representative about issues, concerns, and critical success goals the print buyer has for the job. For example, if a particular blue in a product image is important to the customer - the press operator should know that fact. Having this knowledge shows the customer that the shop is personally involved in the success of both the press run and the customer. It also helps establish better communications, if any color adjustments need to be made.

• When the press operator is satisfied with the color then a press sheet should be pulled and filed as "first press operator OK." Press operator OK'd color sheets can be used later by the printshop to identify and evaluate print manufacturing issues from prepress through the pressroom.

• When the customer arrives at the press, the press operator should introduce themselves.

• When the customer is at the press the press operator should stand aside and allow the customer "breathing room" to examine the press sheet against the proof.

• Tools such as Pantone swatchbooks, ink draw downs, loupes, note paper and pens for customer use should be readily available.

• The press operator should try and use correct terms and use them consistently. For example, do not use the term "blue" if you mean "cyan."

• Encourage the customer to explain what concerns they have rather than tell you how to fix them. Their role is to identify the problem - your role is to know whether, and how the problem can be fixed.

• If you make a press adjustment to fix an issue, tell the customer what you will be doing and how you feel it will fix the problem. This helps confirm to the customer that you correctly understood their issue and it also helps educate them which, in turn, will make future press checks go quicker.

• If there are any issues that you have with the press to proof match - let the customer know that right away rather than have them discover it themselves. Doing so tells the customer that you are not trying to hide anything from them. It also helps establish a mutually respectful environment.

• Be aware of time - every minute the press is idle the company is losing money. Remember, you can get press sheet sign-off with notes to cover some issues (e.g. "OK for color - but must remove all circled spots and hickies). Don't rush the customer, but don't let them dally at the press either.

• Some shops will have a "light room" where customers can take the sheet to view it under "standard" office lighting. This helps mitigate metamerism and substrate fluorescence issues.

• Make sure that the OK press sheet is signed and dated by the customer, the sales representative/CSR, and the press operator. Any continuing issues to be dealt with later should be noted on the sheet.

• Have a cardboard tube ready so that OK'd press sheets can be taken away by the customer.

• Thank the customer for attending the press check.

Press check basics for the print buyer
The role of the print buyer at the press check is to directly communicate their presswork concerns and acceptance with the press operator in the presence of the sales person to help ensure that any color issues are dealt with according to the customer's requirements.

• Once you get the call from the printer, gather up any material related to the job, samples, proofs, spot color draw downs, paper samples, mock-ups, folding dummies, etc. Also, make sure to bring loupes, color swatchbooks, scissors/x-acto knife, pens and notebooks.

• It's a good idea to get an imposition proof from the printer so that you can check three things; are there any potential inline color issues, are pages on the press form imposed the same way as they were on the imposition proof, and finally when the sheet is backed up on press do the pages back up correctly.

• Arrive at the printshop on time. Identify yourself at reception and explain why you are there. Then wait for the sales rep or CSR to be escorted to the waiting lounge or press floor.

• If you are part of a group attending the press check, identify which single individual will be the lead. That is the one person who consolidates the opinions of the folks attending the press approval and therefore the one who speaks for the group to the press operator.

• While waiting to go out to the press floor, ask for an initial make ready sheet that can be checked for content issues like substituted fonts, low resolution images, missing graphics, etc. This will reduce time wasted at the press when doing the color approval.

• At the press, introduce yourself and your team to the press operator. Wait to be invited anywhere near the press console.

• Do not touch or use any equipment at the press unless you specifically ask permission first.

• When you are offered the sheet for examination, ask the press operator if they are happy with the sheet and if they have any concerns/issues with it.

• Engage your sales representative for input and guidance with any thoughts/concerns you have. Tap into their experience.

• Recognize that time equals cost so be focused on the task at hand. If you are working with a team, assign checking roles to each. For example, someone checking registration, another checking for hickeys/specs, low resolution photos, swapped or dropped fonts, etc.

• If you are alone, have a written, organized, step by step yes/no, pass/fail procedure to checking the press sheet . Typically the process goes like this:
1) Is it printed on the correct paper? If a specific paper grain direction was required ensure that it is running in the correct direction.
2) Is it in register?
3) Over all, does the press work color align with the proof? Are there any obvious color issues?

4) When critical color alignment is required, cut the press sheet through the important color and overlay that section of the press sheet on the proof. Colors that may appear correct when compared side by side may appear different when directly overlaid.If you cannot clearly see where the press sheet ends and the proof begins you know you have a critical match.

5) Use your reference material to confirm the correctness of special/spot/brand colors.
• If you have any color concerns/issues, try to describe them clearly and unambiguously. Then describe just as clearly and unambiguously what you want to see. Do not tell them how to fix the issues. Your role is to identify any problems - it is the press operator's role is to know whether, and how any problems can be fixed. You can ask whether a solution you thought of might solve the problem. For example, you could say: "I think this area is too red. Would reducing the Magenta a touch fix it?" Phrasing a suggestion as a question can also help your press operator better understand your meaning according to how you describe the problem.

• Try and use correct and unambiguous terms and use them consistently. For example, do not use the term "blue" if you mean "cyan." Try to avoid terms like: "This area is too hot" or "Can you punch it up a notch?"

• If a press adjustment is made to fix an issue, ask the press operator what they are doing and how they feel it will fix the problem. This helps you to better understand the print production process, and its limitations, better.

• Most press operators will try very hard to achieve what you’re looking for, however, once they've made their press moves and you are still not satisfied it will be up to the sales rep to authorize trying anything else. If it's a really serious issue, the sales rep may stop the press and pull the job.

• Keep in mind that the start/stop/start/stop press cycling during a press check means that the press is not yet running in a stable fashion. Once the press OK is complete and the press is running at optimal speed, some small color issues will clear up by themselves.

• Be aware of time. Respect the printshop's need to maintain their production schedules. Remember, you don’t need to remain until the sheet is absolutely perfect. Just mark it as “OK with changes as noted.” (e.g. "OK for color - but must remove all circled spots and hickies).

• Some shops will have a "light room" where you can take the sheet to view it under "standard" office lighting. This helps mitigate metamerism and substrate fluorescence issues.

• Make sure that the OK press sheet is signed and dated by the person in your team who has authority to take responsibility. Any continuing issues that are to be dealt with later should be so noted on the sheet.

• Ask for a few copies of the OK'd sheet to take away with you for your records.

• Thank the press operator and crew for their performance during the press check. They really appreciate it and will remember you in a positive light during your next press check.