Inks beyond CMYK, Hi-Fi, and Pantone - the world of effects pigments

Printers and their customers are always looking for new ways to add value and a creative spin to print. When conventional CMYK, Hi-Fi, and Pantone spot colors just don't have the impact - it's time to look at the options available with effects pigments.

Here is a run down of the most popular effects ink pigments. Savvy printers will pretest and, based on their understanding and relationship with their customers, make them aware of the creative opportunities these inks provide.

Photochromic inks
Arguably one of the most popular of the effects inks. Photochromic ink undergoes a reversible color change when exposed to UV light. The color change is immediate and reverts to its original color or becomes colorless when the light source is removed. This ink is available in wet or dry offset and flexographic printing.

Austria Solar's 2011 annual report uses photochromic inks to parallel the company's business. It ships in a foil package. Open it under indoor light and all you’ll see is an embossed cover followed by blank pages. However when exposed to the sun the photochromatic inks react and the content is revealed. The report is the creation of agency Serviceplan and Creative Director Cosimo Möller.
Photochromic inks are available in colorless-to-color and color-to-color formulations.
Photochromic ink viewed under office lighting.

Photochromic ink viewed under sun light.
Thermochromic inks
Thermochromic inks are temperature-activated. When rubbed, held in the hand, or exposed to differing temperatures the ink changes from a colorless state or to another color and quickly reverts to its original color.
As with photochromic inks, thermochromic inks are available in colorless-to-color and color-to-color formulations. The temperature when the color change occurs can be predetermined - e.g. color appears at 72°F and becomes colorless at 90°F or color appears at 81°F and becomes colorless at 90°F.

Hydrochromic
This ink is activated by water, not sunlight or heat. A white hydrochromic ink just looks like white ink. When water is applied, it disappears and the image behind it appears. When the water dries, the image goes back to white.

UV Fluorescent
These inks are normally invisible as printed but fluoresce under UV light. There are two types; single long wavelength (360 nm) and dual which fluoresces one color under short wavelength UV (250 nm) and a different color under log wavelength UV (360 nm). Typical UV fluorescent color inks include yellow, green, blue, orange, and red. These inks are often used in banknote printing. This ink is available for wet or dry offset, flexographic and gravure printing.

Optically Variable Ink
This ink contains minute flakes of metallic film which, when viewed at different angles, morphs from one color to another very dramatically. This ink needs to be printed with a fairly heavy weight to get the best results which makes the ink feel almost embossed on the substrate. The ink are very expensive and therefore is usually printed in small areas. The most common color changes are brown to green (and vice versa) as well as red to purple. It is typically used for passports and driver's licenses.

Bleeding
Bleeding ink prints in black but when exposed to any aqueous solution it will produce a red stain - even when touched with just a wet finger. This ink is only available for use with dry offset printing.

Fugitive Ink (water based)

Fugitive ink works similarly to bleeding ink since when exposed to water or an aqueous solution the ink runs. These, also, will be found on checks and if you are to wet your finger with saliva and wipe across the background, you would see the ink smudge.

Coin Reactive
The image printed from this ink is white or transparent. The image is revealed when the edge of a coin is rubbed over the ink. Coin reactive ink cannot be scanned or copied.

Erasable
Erasable ink is used on the background of a document. If an eraser is rubbed on it the ink rubs off in that area. The ink also reacts in the same manner as solvent/chemical reactive inks do. Erasable inks are typically used on scenic or pantograph backgrounds on checks and certificates. This ink should not be used for documents that will go through a laser printer.

Iridescent
Iridescent ink is a translucent pearlescent ink which, when viewed at different angles, creates a subtle change of iridescent hues. It is available in blue, red, green, gold, and silver.

Metameric Pairs
Metameric pairs are two inks that appear similar in color under one set of light conditions but are visibly different under another set.

Puff Ink
Puff ink rises and expands ("puffs") when exposed to a heat source.

Glow in the Dark Ink
This ink radiates a bright light green color after being exposed to bright light and then placed in a relatively dark environment.

Penetrating Ink/Indelible Ink
Penetrating inks contain a penetrating red dye that goes into the fibers of the paper and will show through to the back of the document. Penetrating inks are commonly used on the arabic and MICR numbering of negotiable documents to deter forgers from trying to scrape the number off from the document. If the number is scraped off the red stain remains on the document. Penetrating inks are available for letter press or wet offset printing.

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.

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.

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?

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.