If the substrate is the fifth color of printing, then consistency is the sixth: the quality that gives the laydown of ink or toner its recognizable character and unambiguous visual identity, job after job.
The perception of color consistency is the result of making sure that everything in the print run has taken place according to specifications and that what was produced accurately today can be replicated tomorrow. By harmonizing prepress and press techniques with design objectives, printers deliver the stability that brand owners prize above all in the look of their packaging and labels.
As providers of consistent color, says Lou Iovoli, senior VP at custom label printing specialist Hammer Packaging, “we are stewards of brand integrity.” This means guaranteeing that there will be no misleading differences in color between the first label produced and any of the millions that follow it.
He notes, as an example, that a label color lighter in appearance than what the shopper previously purchased might convey the mistaken impression that the label has faded and the product underneath it is past its sell date.
At first glance, “consistent” color seems to mean the same thing as “repeatable” color: a preferred look that doesn’t change. But, as packaging and label printers know, one is the precursor and the foundation of the other.
“I would define ‘consistent’ color as color that does not deviate during a press run once you have achieved an accurate match to your target,” Jeffrey Dieter, director of technical services at Diamond Packaging, said in an email in response to a question about the difference between the two terms. “Repeatability is when you can accurately achieve your targets [in] every press run.”
Iovoli explains that consistency is needed in generating repeatability. But, repeatability isn’t self-sustaining – it has to be maintained from run to run with the help of best practices. As Steven Smiley, an expert in color who runs consulting firm SmileyColor & Associates, stated in an email, issues can arise “where process control and variation is not monitored and compensated for to keep the system stable.”
Running to data – prepress color values, plate curves, ink densities, press profiles, and other parameters – is what enables the control and makes color both consistent and repeatable.
Paul Kaddatz, operations manager at Neenah, Wis.-based package printer Outlook Group, says that by scanning color bars on printed sheets pulled at intervals during the run, crews can check color for deviations from spec. It is then possible to get back to a “green number” – the desired printing condition – at the console by correcting the inking and making other adjustments on press.
Proceed Without Proofing?
In some cases, running closely to numbers can reduce or even eliminate the need for physical proofing, as Kaddatz says Outlook Group has been able to do in up to 90% of its rerun sheetfed work in which the substrate doesn’t change. Jim Zeman, Outlook Group’s director of operations, notes that the practice is to use a contract proof “first time out of the gate” for initial production, but not for repeat runs once customer targets have been established.
Smiley explains, “Today, many brands do not send proofs, only for CMYK overprints in images. Many brands use only spot colors on 80% of packaging. The proof has not been required if the inks are formulated properly.”
But because printing is always prone to variables, proofing retains an important role in the quest for consistent color.
Iovoli points out while proofing systems are relatively simple and stable, a press is a complex machine with many moving parts and a tendency to change its performance over time. This means recalibrating the proofing system accordingly and not relying solely on running to numbers, which may not always give sufficient guidance to hit the intended color targets.
Dieter states, “Contract proofs are valuable references so that there are no surprises. They can be an additional check that everything is in calibration.” A contract proof, he advises, “tells you whether you’re meeting the intent that the designer had.”
Honoring the intent begins with press fingerprinting, a process that determines how the press prints and indicates how the printing can be optimized for the reproduction standard that the job requires. Fingerprinting, says Iovoli, lets Hammer Packaging be confident that all of its press platforms will support the “common condition” it creates for each job: a profile of the inks and substrates it consists of and the color characteristics it must display from process to process.
Level of Confidence
Fingerprinting, in other words, “should be a confirmation that consistent print can be obtained,” Smiley says. The routine, notes Kaddatz, verifies that “the press is level” and able to meet the requirements of maintaining Outlook Group’s G7 Master Printer certification for flexo and litho production. (Hammer Packaging and Diamond Packaging have also earned G7 Master Printer certification from IDEAlliance.)
The goal of fingerprinting, according to Dieter, “is to get your press to a calibrated state and print to a standard, either a custom standard or an industry standard such as SWOP, GRACoL or FOGRA.”
The process involves running a test form on press, measuring solid ink values, and bringing the L*a*b* values of each of the four process colors within range of the chosen standard. Then comes examining laydowns and dot structures for mechanical issues as doubling, slur, gear streaks and over-emulsified ink.
“This puts the press in a predictable and controlled state,” Dieter says. It also yields the data needed to compensate for TVI (tone value increase) in the printing plates. “If the data meets the criteria for the targeted standard,” he adds, “you have a good set of plating output curves to use.”
The ink dispensed to the plates is an essential ingredient of consistent color. Javier Robles, director of technical services for INX International, notes that an ink can be formulated in different versions for different kinds of packaging applications so that the branded color the ink represents will be uniform throughout. Results should be similar as long as “the substrates aren’t wildly different,” he says.
Nor should there be any need for “tweaking” inks on the printer’s end if communication between the vendor and the printer’s ink room has been good. Tweaking only defeats the purpose of a carefully compounded ink, Robles cautions.
According to Smiley, ink vendors, printers and creatives have an ally for consistency in CxF (Color eXchange File format), a technology introduced by X-Rite in 2000 and approved by ISO in 2015 as an open standard for color data exchange and verification across the supply chain.
“Defining colors as CxF provides data for designers to align on brand colors, not a guide color,” he says. When ink makers and printers share color information in the CxF format, they have “proper communication tools to align pigment selection in ink formulation and tools for process control on press.”
Monitoring and regulating pressroom conditions is another sine qua non for obtaining good, consistent color printing. Some of them are obvious; others can be downright mysterious until the causes of their ill effects have been diagnosed (see sidebar on page 20).
The No. 1 environmental factor in color reproduction, according to Kaddatz, is humidity. “It affects stock drastically,” he says, both in sticky summers and low-moisture winters. This is why Outlook Group climate-controls and humidifies production areas as needed and gives every batch of stock between 24 to 48 hours of acclimation time near to where it will be printed before attempting to run any of it on press.
Inspect all incoming raw materials to be certain that the substrate being printed today is the same as the last time the job was produced, Iovoli advises. He’s also a stickler for keeping production equipment in peak condition. “To be at the top of your game,” he says, “there’s no substitute for preventive maintenance. It’s got to be done.”
Here, the key to preserving consistency is in the details. “Striping the rollers is incredibly important on an offset press,” notes Smiley, referring to a crucial function of the inking train. Robles, similarly, declares that “roller maintenance is huge” despite the fact that “it sometimes takes the back seat” in preventive maintenance routines.
Production issues aside, correctly assessing the brand owner’s intent may be the most fundamental element of color consistency. A brand might package some of its products in folding cartons, others in flexible pouches and others in containers with labels or shrink sleeves. The brand owner, rightly, wants to be assured that colors, brand marks and images will share a common visual identity in all of these formats.
But, some of the responsibility for that rests with the customer.
“Color communication is critical in cases like this,” Dieter declares. “I think a brand owner needs to take a step back and look at how many print processes and substrates are being used. From that, identify the closest match that can be achieved as an average of all variable processes and substrates. Once a best possible match is identified, it needs to be shared with the print provider.”
A Jarring Difference
Sometimes, sharing means helping customers understand what “best possible” means in actual production terms. Dieter recalls a press approval in which the customer’s color reference was a jar with a spot color that Diamond Packaging’s pressroom was expected to match. A drawdown had confirmed the match in the spot ink, but the customer insisted that the color on the jar was the right one to run to.
In fact, says Dieter, the customer’s sample proved to be off the mark by a factor of ∆E 14, whereas the ink’s deviation was just ∆E 1.5: close to the smallest color difference the human eye can see, and acceptable as a match in most instances.
Smiley says that adherence to industry standards is the best way for printers and brand owners to avoid ambiguities and misunderstandings about color. He points to ISO/PAS 15339, a data-driven methodology for achieving optimal reproduction across a broad range of substrates and printing processes, as an example.
ISO/PAS 15339, as Smiley describes it, “provides data sets that can align with all packaging products, from small gamut to a very large gamut.” Because the data sets share the same near-neutral calibration, they create a common appearance in the printing conditions they apply to.
Smiley says he hopes to see more packaging printers embrace protocols like ISO/PAS 15339. When brand owners know that they have, he assures them, “the work just pours in.”