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.

Technical tips for creating brand colors

Color is one of the most critical components in creating brand identity and while there is a fair amount of information on the psychological and cultural aspects of color - there's very little information on the technical issues that need to be considered when developing a custom or brand color.

Brand colors are custom (a.k.a. line, spot) colors that are any single color (typically other than cyan, magenta, yellow, or black) that are usually printed as a solid area of ink on a dedicated press unit.

There are two types of custom colors -
1 Proprietary
2 Referenced.

Proprietary custom colors are colors that are created by the brand owner or their creatives. Coca-Cola red and Kodak yellow are examples of proprietary brand colors.
Referenced custom colors are usually published in color palettes that are to be used by creatives to specify spot colors.

The main brands of referenced custom color palettes are:

Pantone, the dominant spot color printing system in the United States and Europe.
Toyo, a custom spot color system that is popular in Japan.DIC, Dainippon Ink & Chemicals, Inc., another popular Japanese custom color system.
ANPA a palette of 300 colors specified by the American Newspaper Publishers Association for spot color usage in newspapers.
HKS Hostmann-Steinberg Druckfarben, Kast + Ehinger Druckfarben und H. Schmincke & Co. a custom color system containing 120 spot colors and 3250 tones for coated and uncoated paper.
The main benefit of creating a proprietary brand color is that it is unique to the brand thereby enhancing the brand's unique identity. The downside is that the creatives/brand owner are required to create their own system of specifying, communicating, and manufacturing the color.

The main benefit of using colors from a reference custom color palette is that the system of specifying, communicating, and manufacturing the color has already been built. The downside is that the color is not unique to the brand and can be used by others, potentially creating confusion in the marketplace.

When creating a new proprietary custom colors to be used for brand identity keep these technical tips in mind:

1- Humans have very good color discrimination for greens and much less for blues, reds, yellows, and purples.This means that they can more easily distinguish between subtle differences in two similar greens than they can two similar reds. It also means that there are more green custom color options than there are red.

2- In offset lithography, the range of possible greens is larger than that of reds, blues, and oranges

3- Humans have poor color discrimination when hues are very saturated - I.e. saturated colors will tolerate greater variation in reproduction before a color shift is noticed.

4- RGB, CMYK, and Hexadecimal values do not actually define colors because those values are device dependent. I.e. it does not, for example, tell us the specific hue of the Cyan ink being used - a factor that will change depending on the ink manufacturer.A demonstration by Flint ink of the influence on ink color resulting from differences in the substrate upon which the ink is printed.
So, a color defined using CMYK values will also look like a different color when printed on newsprint, in a magazine, or in a brochure due to the differences in the specific CMYK inks used and the substrates they are printed on.
Instead, define the color using CIEL*a*b* reference values since these are device independent. If RGB and/or CMYK values must be provided then make sure that the version or source is included (e.g. sRGB, Adobe 1998 RGB, CMYK/SWOP, CMYK GRACoL 7, etc.) to help minimize variation.

5- Confirm that the proposed custom color is within the color gamut of the expected most used reproduction process.An application like Chromix ColorThink enables the CIEL*a*b* values of the custom color to be compared with the color gamut of the system that will be used to print it and determine if it is reproducible or not - i.e. in, or out of, gamut.
If the custom color is within gamut, it means that it can be simulated by mixing screen tint percentages of the primary inks of the print process.

6- Make sure, by testing, that the ink pigments used in the custom color will not shift hue because of heat e.g. during lamination or react with other inks or to oxygen e.g. Reflex Blue.

7- Avoid using fluorescing agents in the ink.

8- Use certified sample color swatches and CIE L*a*b* values to communicate color globally.Ideally the sample swatches should be as large as possible since the perception of color changes with coverage area. Also include a "Hi-Lo" reference which shows how much darker or lighter the color can be and still be in specification. If possible, include a CIEL*a*b* Delta E value for how far the hue of the color can deviate while still being within specification. Include the information about how the Delta E value is to be calculated (e.g. Delta E 98, Delta E 76, Delta E CMC, etc.)

9- Prevent brand bloat by consolidating/rationalizing custom color libraries. Retire old colors and consolidate colors that are very similar.

Addendum
A number of readers questioned my statement that humans have very good color discrimination for greens and less so for other colors. In the below video Eric Fossum, image sensor engineer and primary inventor of the CMOS sensor used in digital cameras, mentions the color sensitivity of the human eye during a recent talk at Yale University.

The issue of metamerism in print production

With print, each medium in the production process from original art to image capture, monitor display, proof, and final presswork has its own unique spectral characteristics. The majority of color reproductions utilize cyan, magenta, yellow, and black inks or colorants. But none of those inks are exact spectral matches to the media originally used to produce the original art. As a result, the inks used to create color reproductions are combined to simulate an artwork, but only under one industry standard light source - referred to as "D50" or "D65".

During production the integrity of the reproduction of artwork is monitored by making comparisons, for example, original to its copy or proof to presswork. The two colored objects are referred to as a metameric pair if they match under at least one combination of illuminant and observer and not match under at least one combination of illuminant and observer. They must also have different spectral response curves.

So, the phenomenon of metamerism begins with comparing a pair of colored objects. For example the color of the back door of this truck compared with the color of the rest of the truck.
In the truck example the pigments used in the paint were not the same for the back door compared with the rest of the truck. The two colors would have matched under the artificial lighting that was used when the door was painted. However, under sunlight conditions the door and body no longer match causing "metameric failure."

In this case metameric failure is a benefit to the prospective customer since it warned that the door was painted at a different time from the rest of the truck. Possibly it had been damaged and subsequently repaired. Unfortunately the effect of metameric failure in print production usually causes problems rather than benefits.

How metameric failure impacts print production

There are four types of metameric failure commonly encountered in print production.

Sample metameric failure This is the most common cause of color matching problems. The truck example above is an example of sample metamerism. Because proofs and press sheets form metameric pairs, this problem typically shows up when presswork matches the proof in the light booth at press but no longer match under the lighting conditions where the presswork will normally be used, e.g. a package in a store, or brochure in a home environment. Other examples of sample metameric failure include product samples (e.g. fabric) compared with their reproduction in proofs, presswork, or computer displays. Or process color screen tint builds. They may match under one lighting condition but not another. Sample metameric failure can also happen if two prints using very different technologies - such as offset print vs silkscreen print - are compared under different lighting conditions.

Observer metameric failure This can happen because of differences in color vision between observers. Although the common cause is colorblindness, it is not uncommon among "normal" observers. As a result, two spectrally dissimilar color surfaces may produce a color match for one person but fail to match when viewed by a another person. Observer metameric failure is the reason there were 31 individuals tested to derive the original 1931 "standard observer" values adopted by the ISO and that are still used today as the basis for the majority of color science.

Field-size metameric failure This occurs because the relative proportions of the three light sensitive cone types in the retina of the eye vary from the center of the visual field to the periphery. The result is that colors that match when viewed as very small, centrally fixated areas may appear different when presented as large color areas. This is the reason why color painted on a wall may appear different than the paint chip used to select the color even though they match when the chip is placed on the wall. In print production field-size metameric failure typically occurs when small PMS swatchbook samples are used to specify a PMS color that will cover a large press sheet area.

Geometric metameric failure Normally, material attributes such as translucency, gloss or surface texture are not considered in color matching. However here, identical colors appear different when viewed at different angles, distances, light positions, etc. Geometric metameric failure is most often seen when using metallic inks or paper, and specialty ink coatings or papers.

Tips for dealing with metameric failure

1. Be aware that it exists and may be the "simple" issue causing any color match issues.

2. If color needs to align across different lighting conditions choose pigments carefully or make the ink formulator aware of that requirement.

3. Control your lighting conditions - both for producing prints, final viewing (where possible), and for critical evaluation. The industry standard light source is referred to as "D50" or "D65" (5,000° Kelvin (North America), 6,500° (Europe).

4. Invest in PIA/GATF RHEM light indicators for everyone in the production chain that is involved in evaluating and approving color. RHEM light indicators are small (2" x 3/4") paper stickers with a unique printed design that uses metameric failure to indicate whether or not the viewing conditions are 5,000° K or not.Stripes appearing in the RHEM sticker indicate the lighting conditions and therefore whether a color evaluation can be made.
The stickers can be affixed to proofs or simply carried in a protective wrapper in purse or wallet.

5. Printshops should have viewing areas away from the press that allow print customers to view the presswork under typical lighting conditions (fluorescent and incandescent).

6. Be sure that all instruments (e.g. spectrophotomers) that are used for color evaluation are set to the same standard illuminant, D50 or D65, and same observer angle (typically 2°).

What is wrong with this scene?

The Pantone Hotel - a bold new color space

Pantone, the international brand best known for its spot color palettes, has opened a hotel located in the heart of Brussels just a 5-minute walk from the fashionable Avenue Louise and Metro Louise.
Designed by Belgian interior designer Michel Penneman and Belgian architect Olivier Hannaert, the Pantone Hotel is a boutique property housing 59 austere guest rooms which are described as "works of art" by Pantone.Each of the hotel’s seven floors are schemed with different color palettes to complement guests’ emotions with distinctive hues – from "earth, rich" to "cheerful, warm," "captivating, esteemed, silky" or "fresh, eager.The cost of a night's stay is about the same as the cost for one of the company's color swatchbook guides.

The hotel also offers the Pantone Lounge, which offers cocktails suited to guests' moods, such as Pink Champagne PANTONE 12-1107, Lemon Drop PANTONE 12-0736 or Daiquiri Green PANTONE 12-0435.
PANTONE Color consultants are also available by appointment for informal color consultations or to present educational seminars on color psychology and trends.

The Pantone hotel follows the company's move into other branded merchandise such as mugs and clothing and includes amenities from the collection and the largest selection of Pantone products worldwide.
More information about the Pantone hotel can be found HERE.

Choosing the right screen angle for over-printing spot colors

To decide which screen angle to use when a screened PMS/spot color overprints a 4/C process image you will need to look carefully at the image that you will be overprinting.

The basic rule is to use the screen angle of the least prominent (or missing) screened process color that will be underneath the screened spot color.

For example, if there's no screened black under the spot color - use the Black angle, if there's no Cyan use the Cyan angle, etc.

Try to avoid using the Yellow screen angle because in standard screen angle sets yellow is only 15 degrees away from C or M. As a result moiré is always there but it is usually not visible because the yellow is so pale. The moiré can become visible however, if the yellow becomes contaminated - or if it is used for a dark spot color.

For example, in the graphic below, the left image is Cyan (at 105°) overprinted with process Yellow at the standard 90°. The moiré is barely visible. However, in the center image overprinting Cyan with PMS 144 – a very dark yellow/orange color – using the same Yellow screen angle results in the existing moiré becoming very visible. On the right, PMS 144 uses the Magenta screen angle (75°) instead which eliminates the halftone moiré seen in the center image.

Alternatively, you could try running the 5th color using a second order FM screen. If you're using a 175 lpi AM/XM screen then the FM should be about 35 micron because if it's any finer you'll need to create dot gain compensation curves for the FM. Because 35 micron is a fairly coarse screen it is best used for fairly light colors otherwise you may find that the screen is too visible.

Because spot/PMS colors are typically formulated to be printed solid and not halftone screened, make sure that your ink vendor knows that you are going to be screening the ink and the dot size range as well (either in microns or lpi) so that they can formulate the inks accordingly.

Custom, Spot, Brand, and Pantone Colors

Custom, Spot, Brand, and Pantone colors are all examples of custom single printing ink colors other than Cyan, Magenta, Yellow, or blacK. Just like CMYK inks, they filter (subtract) light that is reflected from the substrate.On the left below is a patch of color created with 4/C process screens and on the right the same color using a single custom ink.
Custom colors are typically specified using one or more of the following:
1- a reference physical sample such as a swatchbook, color chip, or physical sample
2- a numeric value that references a swatch or color guide book
3- a formula or recipe to mix ink ingredients in order to achieve the custom color
4- a numeric value that references a color model such as CIE L*a*b*

The Pantone reference swatchbook for its proprietary custom colors, contains a numeric color reference number, sample swatches of the custom color, as well as formulae for mixing inks to achieve the selected color.
Note: There are no specific color tolerances defined by Pantone as to what constitutes an acceptable match when variation naturally occurs.

The corporate brand color reference swatchbook below, mimics Pantone's but adds acceptable "High/Low" reference samples to accommodate ink density variations that occur naturally in presswork.

The primary brands of proprietary custom color systems are:

Pantone, the dominant spot color specification system in the United States and Europe.
Toyo, a popular spot color system that is used in Japan.
DIC, Dainippon Ink & Chemicals, Inc., another common Japanese spot color system
ANPA a palette of 300 colors specified by the American Newspaper Publishers Association for spot color usage in newspapers
HKS Hostmann-Steinberg Druckfarben, Kast + Ehinger Druckfarben und H. Schmincke & Co. containing 120 spot colors and 3250 tones for coated and uncoated paper

The hues for all these proprietary colors are defined using name, ink mix formula, and (not always published) CIE L*a*b* values.

Aspects of the Pantone spot color system

Custom colors are not limited by the gamut constraints imposed by monitor displays or press gamuts that depend on CMYK primaries. About 95% of all Pantone spot colors are within monitor gamut, while only about 34% of Pantone spot colors are within the standard CMYK gamut.
This short video (click on the "play" arrow) shows 1113 Pantone colors (excluding metallics and fluorescents) plotted against the GRACoL7 CMYK gamut. Only 376 PMS colors (33.8%) are actually within gamut for four color process (at 175 lpi) printing.The Pantone GOE color library is very similar to the original Pantone spot color library in that respect since most of the GOE colors fall between the original Pantone colors.

The Pantone spot color library was never designed, nor intended, to be used as a way to specify colors that will be printed using 4/C process CMYK. As a result, because of the gamut differences mean that 4/C process simulations of the Pantone library will, can only provide an approximation and in the majority of cases, deliver disappointing results.

At left a 4/C simulation of the Pantone spot ink color at right.
Some key notions:

1- The CMYK recipes for Pantone spot colors are generic approximations. They do not reflect regional print color standards, nor individual printshop color.

2- Approximately 66% of the library is out of gamut for 4/C process.

3- The specific colors in the library are based on ink mixing formulae - not target CIEL*a*b* color values. The CIEL*a*b* color values included with some applications, e.g. Adobe Photoshop, are only included as a courtesy to assist with conversion to CMYK – they are not the target for the color itself.

4- The Pantone Goe library is not intended to replace PMS but to supplement it (PMS library is ~1089 colors vs Pantone Goe’s 2,058). Pantone Goe spot colors are primarily “’tween” colors and about 400 colors overlap with the original Pantone spot colors.

5- There are no published specifications for acceptable variation of a Pantone spot color due to natural variation on press. Each printer/specifier/customer must determine their own color tolerance specifications.

6- The RGB values in the GOE swatchbook are actually sRGB values-I.e. not a typical printing color space.

Custom/Spot colors in the pressroom
1- CMYK inks are formulated to ISO specifications - there are no ISO Spot ink specifications. This may cause variations in the final color when the inks are prepared at different geographic locations.

2- CMYK inks are designed to overprint (wet trap) - Spot color inks designed to print isolated (dry trap). This can cause unexpected results with overprinting unless they have been specifically custom formulated to wet trap.

3- CMYK inks are transparent - Spot inks are typically semi-opaque.

4- CMYK inks have defined density (ink film thickness), dot gain and trap targets - there are none for Spot color inks.

5- Pantone spot colors are generally not formulated to be halftone screened. Some colors, as a result of the pigment grind used may appear grainy, especially with high lpi AM/XM and FM screens. If the custom spot color ink will be screened, it is best to confirm with the ink supplier that the ink formulation is suitable.

6- Pantone spot colors are often not mixed by the ink vendor, or printer, using the actual official Pantone base colors. This may cause color shifts due to the different spectral qualities of the base inks used (metamerism). To help ensure color consistency when printing at different locations, try to make sure that the base inks used to create the custom color are the same and from the same ink vendor.

7- Spot color inks are typically multi-pigment which may cause unexpected color shifts under different lighting conditions (metamerism).

8- Because of their ink composition, some custom spot colors may shift dramatically when heat is applied or when laminated. Always test before using on a live job.

9- Ink draw-downs, or pulling samples of ink on paper, tests the color of an ink mixture by spreading a thin film of ink on paper with a spatula or by using a tiny tabletop press, generically called a "Little Joe," that holds a 4×6´´ offset printing plate. By using real ink on the paper intended for the job, users get a good prediction of how that ink will look on the actual substrate, allowing adjustments in color and paper selection well before press time. However, since the tabletop press does not use water, as is used on the proper offset press, there can be subtle differences in how the spot color will actually look in the final presswork especially if the spot color will be halftone screened.

Some best practices and tips – primarily for designers and brand owners
1- Wherever possible use/insist on Pantone/Goe base inks to mix Pantone spot colors.

2- When developing custom/brand colors, it is best to use CMYK inks that conform to ISO 12647-2 as the primary base colors. Although this reduces the range of possible hues, it will allow 4/C process printing to simulate the spot brand color accurately in print applications where the spot color cannot be used.

3- When developing custom/brand colors make sure that the ink formulae contain information about the ink vendor of choice.

4- Formula-based custom/brand colors should include reference CIE L*a*b* values. The CIE L*a*b* values should be the target for color and take priority over sample swatches.

5- Custom/brand colors should include a specification for acceptable defined with either a high/low density range or a CIE L*a*b* DeltaE value. 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.

6- RGB values associated with custom/brand colors should specify the source (e.g. sRGB, Adobe 1998, etc)

7- Beware of the effects of optical brighteners used in paper. If proofing paper and final substrate don’t have equal level of optical brighteners then color will probably not align between them - especially in pastel spot colors.

8- The amount of optical brighteners, as can be seen in the below image taken under blacklight, that is used in the Pantone GOE guide (at left in the below image) is higher than in the standard Pantone swatch book (at right below):Because optical brightening agents can fade quickly under normal lighting conditions, this may reduce the integrity of the colors displayed in the GOE guide more quickly than the standard Pantone swatchbook. Therefore, store swatchbooks away from light.

9- The "white" ink used in pastel Pantone and other custom colors is essentially a varnish. As such it will yellow with age and cause a color shift.

10- The only proof of presswork is actual presswork - all off-press proofs share some degree of compromise - especially when proofing spot colors. Press proof whenever possible - especially when the spot colors will be halftone screened. Include any special finishing (e.g. coatings and lamination). Always clarify whether spot colors represented on proofs are valid for color or just place holders. Treat draw-downs of spot color screen tints with skepticism. Treat inkjet proofs of spot screen tints with suspicion and proofs showing spot color overprints with humor.

Pantone Colors and CMYK gamut

This short video (click on the "play" arrow) shows 1113 Pantone colors (excluding metallics and fluorescents) plotted against the GRACoL7 CMYK gamut. It shows what region of the CMYK gamut the PMS colors exceed. Only 376 PMS colors (33.8%) are actually within gamut for four color process (at 175 lpi) printing. A higher resolution video is available - contact me at pritchardgordon@gmail (dot) com for a link to download it.