: Who first discovered CMYK? It has been used for colour printing for many, many years, but who (and when) first discovered that a bright pink colour (magenta), a light blue (cyan), yellow and
It has been used for colour printing for many, many years, but who (and when) first discovered that a bright pink colour (magenta), a light blue (cyan), yellow and black can be mixed to create almost all colours? How did they discover this?
(Or more correctly "CMY" - the Black (K) isn't strictly necessary)
The three- and four-color process was invented by Jacob Le Blon around 1725. His original color model used RYB (red, yellow, blue) and RYBK (red, yellow, blue, and black). He wrote a book called The Coloritto, in which he explains his discoveries and results that lead him to use these set of particular colors and the reason for adding black to his original three-color process to produce more realistic natural colors. You can find the book in the Library of Congress.
It likely depends on what you qualify as 'CMYK'. Other answers have already established that the K is superfluous -- it's there to make printing easy, not because it's required for color.
So that makes us wonder who first established that we could create (most) colors using only three colors ... and I believe that at least in the West, that's credited to the work of Thomas Young who proposed in 1802 that humans had three color receptors, which was extended by Hermann von Helmholtz, and later proven by James Clerk Maxwell.
If we go back further, however, it was Isaac Newton who is credited in 1686 with the discovery of metamers -- that you could combine two colors of light to get something that is perceived as matching a third color even if they don't actually match spectrally.
So ... to summarize ... it's quite likely either the person who gave us Newton's Laws of Motion, Young's Modulus, or Maxwell's Equations ... or the namesake of the Helmholtz Association
There is no single definable point when the CMYK Process Colour printing was discovered. High fidelity process colour reproduction printing has been a gradual series of technical refinements.
The persons responsible are, however, known.
Printed colour reproduction grew rapidly in popularity in the late nineteenth and early twentieth centuries to today, when (excluding newspapers) the great bulk of all pictorial reproductions is in colour. The basic principles of photomechanical colour reproduction remain the same today as there were in 1900, but there have been many important advances over the years that have led to improved quality and lower costs.
The Colour Process for Colour Reproduction depends on several different factors.
First, is the development of the necessary TRANSPARENT inks. As colour reproduction depends on the subtractive system, the overlap of the process colours cannot work with opaque inks that obscure the under-printed inks and the paper (usually) substrate.
The original pigments used in printing inks were mainly inorganic pigments that had a restricted gamut, and, in some cases, poor transparency. The development of organic pigments increased the available color gamut while still retaining reasonable permanence. The major developments were as follows:
The azo colors for ink manufacture developed between 1899 and 1912. Most Yellow pigments are of this class.
The discovery of the tungstated and molybdeated pigments in about 1914. The best process magentas fall into this class.
The discovery in 1928 of phthalocyanine pigments, which made possible the first really permanent brilliant cyan suitable for process-colour printing.
Other developments that led to use of process-colour printing included the four-colour printing press.
The first recorded use of a four-colour lithographic sheetfed press was by the Traung Label and Lithograph Company of San Francisco, California, during early 1932. This offset press was made by the Harris-Seybold-Potter Company of Cleveland, Ohio (now Harris Graphics). Four-colour web offset presses preceded sheetfed presses. In 1926 the Melbourne, Australia, daily newspaper The Argus installed the German-built Vomag web offset machine that had four perfecting (can print on both sides of the same press sheet) printing units. This press was used to print weekly colour supplements and magazines. The Berlin, Germany company of Messrs Dr. Selle and Company were reported as printing four-colour work by web offset in 1926.
The Cottrell Company reportedly made a four colour common impression cylinder rotary letterpress sheetfed machine about 1912, but the thick letterpress ink films (layers) made wet-on-wet (ink "trapping") process-colour work impractical.
The first recorded three-colour (intaglio) prints were produced on a web machine at Siegburg in 1914. A common impression cylinder was on this machine.Around the same time, a multiunit Goss intaglio press was installed at The Chicago Tribune. This machine had separate-unit type construction for each colour. However, it is thought that the first successful gravure process four-colour work on a multicolour machine was not produced until the late 1920s or early 1930s, probably on a machine made by the Albert company.
The specific answer to your question is in this entry:
The primary elements [for the CMYK process colour printing we know today] are a magenta red, a yellow and turquoise blue. These three basic hues were brought to perfection by Herbert E. Ives (1882–1953) and represent the minimum "primary" colours which, in combination, will produce a full array of fairly pure intermediates using average pigments. (Ives used the term achlor for magenta, zanth for yellow, and syan for turquoise blue.) Mixtures of magenta and yellow form reds and oranges. Mixtures of yellow and turquoise form greens. Mixtures of magenta and turquoise form purples. These three, in other words , are the fewest that can be employed to produce a satisfactory colour circle. For rich, powerful hues, however, more than three colours becomes essential.
Prior to, and inspiration for, the CMYK dot automated screen colour printing process as a means to create intermediate colours in a print was by manually using points of pigment. The artists that pioneered the effect known as optical mixture were French painters such as Georges Seurat and Paul Signac in 1886. From a distance we cannot clearly perceive the edges of small shapes. Similarly, from a distance a small areas of colour seem to blend into one another and are seen as a mixture rather than as separate hues. The effect occurs in the eye rather than in the pigments. Essentially, pointillism was the immediate precursor to the 4-colour dot screen used by the modern 4-colour process printing
This effect was the focus of experimentation for a group of painters called the pointillists, who theorized that optical mixture would provide a more dynamic expression of colour than the traditional pigment mixing.
A Canadian engraver, Phillip Desbarates, came up with a similar automated process using lines and dots to make halftones images in Montreal, Canada, who discovered the process for printing for the Montreal Star around the same time (1885). Desbaretes later took his concept to the Currier & ives Co. where porcelain china was decorated with scenes using the early "halftone" process with colour materials.
A collision of events near the turn of the 20th century heralded the 4-colour CMYK printing process we have today using transparent inks and dots.
Creative Color, Faber Birren, Lutton Publishing Compary, 1961
Principles of Visual Perception, Carolyn M. Bloomer, Litton-Van Nostrand Reinhold, 1976
Graphc Arts Photography: Color, Fred Wentzel and Ray Blair and Tom Destree, Graphic Arts Technical Foundation, 1983
Color And Its Reproduction, Gary Field, Graphic Arts Technical Foundation, 1988.
I don't think it is accurate to say that CMYK was "discovered". I am anything except an artist or an historian, so take what I have with a huge grain of salt. But, think about it. Ink is just paint for paper. Any question about ink must refer back to paint, and of course we've been using paint for 8 thousand years. So, the question is not productive. CMYK is an INVENTED system to quantify (industrialize) the color making process and description. Conflating CMYK with the fact (which most 5 year olds know) that colors can be mixed and that three plus black and white give you a huge pallet is not the most useful way to think about it. I'm a technologist, I think of it more like a standardization of color. As paper making got more sophisticated and quality (uniformity and color stability) of the paper improved, and as pigment production improved (but even today, two different batches of almost any pigment is of slightly different color! (titanium white and carbon black might be considered exceptions...), we were able to quantify and standardize the process of creating a multiple color picture. But if you dig in to the pigment (or paper) making process, you'll find that the artists of past centuries made their own paints, some their own pigments, and that uniformity was rare. HTH
CMYK is an improvement over CMY which itself is improvement over RYB model, which has been used for centuries (if not millennia).
It's really hard to tell where one ends and the other begins, especially as some use words "red" and "blue" in more general sense. Eg. George Field's chart from 1841 lists "red, blue, yellow" but his red in our eyes looks closer to magenta than what we today consider as "red". His blue is also suspiciously pale, so his "RYB" chart may be viewed as early attempt of achieving CMY model. We also need to consider that people were working with dyes they had access to - so they could be aware that "proper" blue should be more cyanish, but it wasn't available to them. Move from RYB to CMY was a gradual process.
Adding black is mostly cost-cutting improvement (or workaround for imperfect CMY inks) so I personally would not make a clear distinction between CMY and CMYK at fundamental concept level. The usefulness of black ink varies heavily depending on the actual image being printed.
Wikipedia has nice historical article under RYB color model
According to Joe Scout the first company to use CMYK in printing was Eagle Printing Ink Company and the year was 1906. It was not until 1956 that it became a standard as a result of Pantone trying to streamline the workflow.
This however does not really answer who really invented/discovered the choice of colors, the first scientific literature to mention this appears to be published in 1908. Going deeper it appears that we have a significant problem. It seems that there is a certain ambivalence in the naming of colors. In certain later sources we see that cyan and magenta refereed to as blue and red even as late as 1950's. So language no longer works quite well searching for earlier sources and it becomes hard to follow the lead. Secondly pigments fade so we can not compare easily what they mean. Certainly lot of work of finding the primaries has been done from 18ths century. 
It has been fairly long known that the human eye was sensitive to 3 color wavelengths (called tristimulus values in scientific lore). Some sources attribute this as far back as 1613 . But certainly it was known and verified by mid 1800's see Young–Helmholtz theory. So the sensory primaries were known for quite some time. RGB primaries are chosen to closely match the 3 sensors in our eye. However, a paper does not transmit light, it reflects light. So a paper is usually white, representing maximum reflection. Each ink then subtracts one color off the palette since you need to be able to independently manipulate each RGB channel. This fact was known since Newton . So you need to find the inverse of RGB which simply is CMY. The black color is there mostly, and originally, to avoid registration problems as black is the most common body text color ink. Though black does make it easier to mix certain dark tones.
Of course CMYK printing predates RGB monitors by a comfortable margin of 60 years. CMYK is not derived from RGB but the intuition needed is the same. The authors must have known or indirectly inferred the inner workings of the eye's sensory apparatus. But its not nearly as simple as this as finding good pigments for the job is a journey on its own. Knowing what to look for is not the same as knowing what is there.
Scout, Joe, The History Of The CMYK Colour Model, Club Ink Blog, 2016-05-02. www.clubink.ca/blog/print/history-behind-cmyk-colour-model/ referenced 2016-06-07
Briggs, David. 2006. www.huevaluechroma.com/062.php Weale, R. Ophthalmic Physiol Opt. 2007 Nov;27(6):525-6.
In 1906, the Eagle Printing Ink Company incorporated the four-colour
wet process inks for the first time. These four colours were cyan,
magenta, yellow, and black (also known as key), hence the name CMYK.
It was discovered that these four colours can be combined to produce
an almost unlimited number of richer, darker tones.