When printing packaging, special Spot colors (Pantone) are usually used for brand colors or particular effects and backgrounds in addition to the standard CMYK inks in a CMYK+N approach The use of Spot colors however makes Packaging more expensive and increases carbon footprint in general: more ink, bigger presses, more energy, etc. The usual alternative are expanded gamut printing systems based in 7 colors CMYK+RGB approach which are also expensive and not easy to manage from a technical point of view, with still a bigger carbon footprint in general Tetrachrome instead is a simpler printing system that can achieve an expanded or “enhanced” gamut using only CMYK inks, being able to reproduce most of Pantone colors and all images with a lower cost and a reduced carbon footprint in general, thus being more ecofriendly and more aligned with the sustainable goals of Stora Enso Tetrachrome can be used in Gravure, Flexography, Off-set, Digital and other printing systems and requires some extra technology already developed for prepress as well as a partnership with an ink company as the CMYK inks used are different from the standard in the industr

1. Expanded gamut with CMYK only
The challenge of returning to what CMYK was supposed to be in the first place
A BIT OF BACKGROUND
It was May 2008 and we touched the sky with our hands when the technical jury of Drupa
Innovation Parc granted us a modest stand in the area destined to small companies with
new ideas, we were the only company from South America and that alone was sort of a
privilege and a rarity at the same time
The future was full of bright promises and our project “Tetrachrome” of expanded gamut
with CMYK only for gravure received enough press and interested customers from all
over the World to make us happy and hopeful
I moved to the US to continue working on the project but the financial crisis at the end of
2008 changed everything...
Several years passed afterwards, the granted international patent was not renewed due
to budget cuts and the wonderful software we created for the (at the time) emerging Mac
OS X went eventually to a halt in development due to lack of funds and the difficulty of
reaching the tough international marked of software for a small company born in South
America
But I still believe in expanded gamut with CMYK only, the simple idea of using special
“cleaner" CMYK+ process inks farther away from the center in the Lab color space to
achieve an expanded gamut that allows to print brighter and better pictures and
reproduce Pantone® colors more accurately just with four inks versus the expanded
gamut systems that currently use seven process inks which are really good but also more
expensive and complicated and for vast regions of the World still out of reach due to the
investment and skills needed to put them in practice on daily production
THE CHALLENGE
DuPont® did make CMYK+ expanded gamut work it in the early 1990’s with their first
Digital Cromalin® why can’t we now do it on press?
Pict 1: DuPont® Digital Cromalin that worked with
expanded gamut CMYK+ inks only and was certified by
Pantone® in the 1990’s to reproduce all Pantone colors
within an acceptable Delta E

2. LET’S GO TO THE ORIGINS
Light does not exist, it is just the tiny part of the electromagnetic spectrum that we have
sensors sensible to: Our eyes
And within that small part of the spectrum they work by separately sensing the low
medium and high frequencies that we call Red, Green and Blue respectively (pict 2)
and different balances of these three frequencies produce in our brains the sensation of
all the millions colors we can see by what is called additive synthesis of colors RGB
Pict 2: The basic structure of the human eye and the retina with the corresponding spectral response of the
Red, Green and Blue Cones plus the Rods that sense brightness. In these graphics the three frequencies RGB
are measured by the wavelength in nanometers
Long time ago we humans discovered that by selectively filtering the white light all
colors can also be achieved on passive white media like paper, canvas, plastics, etc. and
when we say “white” it is nothing more than an equally balanced distribution of the three
RGB frequencies that our brain interprets as white.
“Selective filtering” translates in practice onto three basic filters used in what is called
subtractive synthesis of colors: one filter called Cyan eliminates the low frequency or
Red, other called Magenta eliminates the medium frequency or Green and the last filter
called Yellow eliminates the high frequency or Blue
Since the discovery of the basis for the subtractive synthesis in the 1700’s by Jacob
Christoph Le Blon, the technology of the process inks and the printing industry have
progressed a lot specially after the “materials revolution” in the 20th century, but we are
still using the imperfect inks (light filters) that were developed decades ago...

3. Pict 3: The selective filtering of the inks to form colors in our retina is not so pure in reality, involving
complex processes of refraction, diffuse and specular reflection. Plus the spectral curves of the filtering
process itself are far from perfection too
I made a test measuring with the spectrophotometer a thin
tinted filter with a better spectral curve for Magenta+ to
simulate the possibilities of an ink with that characteristics
and compared it with a standard Gracol Magenta ink curve,
the result is the graph at the bottom of pict 3 that shows how
much better a new improved ink can eliminate Green, which
was added to the graph for comparison purposes.
It can clearly be appreciated that the absorption curve of
Magenta+ eliminates better the medium Green frequencies
between 475nm and 625nm and transmits better the Red an
Blue ranges in the 575-700nm and 375-475nm respectively
The challenge ahead to make this concept work is to develop
inks with spectral curves similar to this one or even better
whenever possible. This is the way CMY subtractive color
synthesis was meant to work in the first place.

4. NORMS AND COLOR CONVERSION
Continuing with the discussion in favor of the feasibility of “expanded” gamut with CMYK
only, in pict 5 it can clearly be seen that some colors like “A” and “B” that fall outside a
standardized gamut e.g. FOGRA can fall inside progressively increased CMYK+ gamuts.
And even when a very clean and strong color like “C” = Pantone® Orange 021 will fall
outside anyway, the Delta E difference for reproduce it as close as possible in CMYK is
considerably smaller.
So the secret is printing with non-standard CMYK inks that I am calling CMYK+ with the
highest possible density. And here there is a bit of an extrapolation to be made since
densitometers are only prepared to measure density of standard inks like ANSI Status-T,
etc. thus a spectral measurement will give a much better idea of the printed “strength” of
non-standard CMYK+ inks (more about this later in this article).
Another example of successful use of a more perfect subtractive CMY synthesis was the
old film slides that used exactly that principle
( http://www.kodak.com/global/en/professional/support/techPubs/e27/e27.pdf )
I must clarify at this point that I am not against norms and standards, they are essential
to achieve quality consistency and repeatability in modern globalized and demanding
markets, so if you want to print outside norms extra caution will be needed in uncharted
territory, dealing with making your own internal standards and SOPs, watching by
example that the total ink limit is perfectly accepted by the substrates you are using,
considering that you will be trying to maximize density & ink laydown, etc.
On this topic it was a very nice surprise to find out at the last G7 Idealliance Summit in
Chicago’s Graph Expo 2015, that the organization is planning to work on a possible
norm for CMYK+ in the near future!
Pict 5: Gamut comparison between std. FOGRA, CMYK+ and DuPont® Digital Cromalin
The implementation of the Tetrachrome principle relied also on a special Color Book that
allowed to visually evaluate actual printed colors on different substrates like
pearlescents, metallics, translucents, etc. where the spectrophometers and the standard
color management software encounter some serious limitations.

5. This special Color Book was not only very useful for the prepress stage but also for
customers and designers to see actual printed results before going to press, specially
on those previously mentioned difficult substrates
(This kind of color book is impossible to build in CMYKRGB systems due to the
exponential growth of the impossible number of color patches that would be needed)
And here is a gem of simplicity: the 5940 patches testchart that is used for the
fingerprint of the press and build the color profiles for the software’s color management
to work, is the same that is used to build the Color Book, just cut the pages, put them in
a binder and send it to the prepress department, the designers and the customer (Picts 6
& 7)
Pict 6: Full Tetrachrome 5940 patches color chart used for both fingerprinting the press and later make a
Color Book to be used in Prepress, customer approval and designing stages
Pict 7: Color Book made by simply binding the testchart pages
After scanning the testchart with the spectrophotometer and creating the color profiles
in spectral mode, (which is important together with the high number of patches = 5940
to give more accuracy to the system) the software had a “Patchfinder” module (pict 9)
that allowed to select and locate the closest of the 5940 color patches to match any
given color entered either by measuring it with a spectrophotometer, or input the Lab
values or Pantone® number.

6. Pict 8: Scanning the testchart and measuring an individual color with automatic and handheld
spectrophotometers to build the color profile and enter an individual color into the software respectively
Pict 9: Patchfinder module that automatically located the closest color among the 5940 patches of the Color
Book with the feature of fine tuning the color after visually review it printed on the actual substrate

7. LET’S GO GAMUTS!
Experimenting even further I measured with the spectrophotometer some other thin
tinted filters for Cyan+ and Yellow+ with a better spectral curve than current standards
to simulate again the possibilities of new inks to be developed with that characteristics
and the result is the graphs in pict 10 and pict 11 that show the results in terms of
spectral response and potential gamut coverage respectively
Pict 10: Comparative spectral response of 3 prospective Pigments+ to do a better selective filtering in the
CMY subtractive color synthesis and thus potentially achieve a bigger gamut and color reproduction
Pict 11: Comparative gamut of prospective inks CMYK+ vs a standard Gracol, showing also the Delta E color
difference for Magenta+ which in this case is the ink with more difference from the standard

8. CONCLUSIONS
The expanded gamut with CMYK only offers not only a more simple and cost effective
way to make reproducible in process printing more spot colors that otherwise would
need an extra plate on press, it also offers the potential advantage of more colorful and
vivid pictures for special cases like Sci-Fi cartoons or photos destined to cultures where
more colorful images are desirable like China or India just as an example (pict 12)
Pict 12: Comparison between image reproduction with standard vs expanded CMYK+ gamut
(The difference has been exaggerated for explanation purposes since this magazine itself prints with a
standard gamut thus intrinsically unable to reproduce the intended example adequately)
The technology available today could potentially allow the development of printing inks
based on improved pigments and bases that were not possible few years ago, DuPont®
already did it in the 1990’s for color proofing with the inks for the Digital Cromalin
Other innovations also recently available in flexo like hollow-concentric dots and
textured HD solids combined with new anilox technologies and hybrid halftone screens
for small dots have considerably increased the possibilities to print high quality CMYK
process runs with higher densities, more homogeneous ink laydown and smoother
transitions in highlight areas even fading to zero percent dots without issues
All this combined with more effective drying systems based on UV curing inks and the
addition of optical brighteners to some printing substrates or varnishes also contribute
to the potential achievement of a bigger gamut in the press (Metamerism could be an
issue that can however fade over the next years due the rapid change to artificial light
sources with more UV content than the classic tungsten bulb)
The future could hold for expanded gamut CMYK+ systems a brighter and wider horizon
than expected...
Antonio de Llamas
was Prepress Production Manager at Diadeis NY
Professor of graphic technology and developer
of a patented color management system
for flexible packaging in gravure and flexo