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Tricolor and Process Printing
Thomas Young’s investigations into the wavelengths of light in 1801 led to the science of light spectra (Spectroscopy). He theorized that the human eye could not possibly contain all the receptors needed to interpret the great number of nuances of color found in the visible spectrum, that the eye must have a way of simplifying this stimulus. After further investigation by Hermann von Helmholtz, it was theorized that primates have three classes of cone shaped sensors in their retinas allowing them to only perceive the red, green, and blue wavelengths of the electromagnetic spectrum. While there continues to be some scientific debate over how humans are able to perceive additional colors beyond these three, it was realized since Sir Isaac Newton’s time that colors are just the minds reaction to differing wavelengths of energy. Color has no existence in reality, the eye only perceives light. After studying this phenomena in 1855, the Scott physicist James Clerk Maxwell proposed a theory that the mind could falsely be made to think it was perceiving full color by only stimulating it with mixtures of the red, green, and blue spectra of light. Maxwell further proposed that if three black & white photographs were taken of the same scene, each shot through a red, green, or blue filter and then turned into transparencies, they could be made to recombine into one full spectral image by projecting them back through the same three filters. Thomas Sutton, lecturing on Maxwell in 1861 put his theory to the test with a lantern slide show where he created the first color photographic based image. Though remarkable, the results was far from perfect. The basic problem lay in the photo emulsions of the time, which were only sensitive to blue and ultraviolet wavelengths.
Ducos du Hauron would later apply these same principals to color printing where the limited pallet was meant to optically blend into new hues unlike chromolithographs that relied on many local colors for direct representation. He patented the tricolor printing process in 1868 and produced the first color printed image using it in 1877. Despite its economy the results were still lacking rendering it noncompetitive.While tricolor printing was a great innovation it remained much better in theory than it was in practice due to the poor color sensitivity of photo emulsions. Things began to change with Hermann Wilhelm Vogel’s discoveries in 1873. He found that by adding specific aniline dyes to photo emulsions they would become receptive to all colors except red. Within a year this problem would also be solved when Edmond Becquerel discovered that chlorophyll added to emulsions would sensitize it to red. It was not until 1881 however that the stability and slowness of these additives were all figured out allowing Frederick Ives to developed a workable panchromatic film emulsion that captured the full spectrum of light. It would take much more time however to perfect it as the values rendered were skewed due to the varying light sensitivity of the different dyes
Even though panchromatic emulsion still produced a black & white photograph, the different color filters that could be placed over a camera’s lens were finally able to accurately separate out different colors of the spectrum within the same scene. When photomechanically transferred onto plates and printed in corresponding additive colors, it created the illusion of a natural color photograph. Natural color became a term used in printing to differentiate the colors captured through photography from those hues chosen by a retoucher in a printing house or painted in by a colorist. All images produced through this method were generally referred to as photochromes in their day, though we now only use the same term or just chromes for similar postcards manufactured after 1934.
(See the Guide to Color on Postcards in the Guides section of this site for a more in depth look at the evolution of color printing.)
Tricolor Lithograph: The Ives Process Company issued this very early card as a sample of their unique ability to create color separated plates from filtered photographs for use in tricolor printing.
Lantern Kromskop: This illustration depicts an Ives Lantern Kromskop dating from 1895. It was able to project three black & white transparencies that were exposed through color filters through the same three filters to produce a natural color image.
While the ability to render full color images with the use of only three colors should have dramatically reduced printing costs, it did not work so well in practice. Even with the aid of Trichromatic cameras, which few could afford, the entire process was still very time consuming and cumbersome. Images shot at close distances were usually off register and anything that moved would appear as a ghost of a single color. Mistakes were costly and this complicated process did not find a wide audience among commercial printers. Tricolor separation proved far more valuable in creating slides for magic lantern shows, which were often projected through the Kromoscope, one of Ives own inventions. This would eventually evolve into Cinemascope, a tricolor movie system that continued to be used all the way up into the 1960’s. Even though noted photographers like Sergei Mikhailovich Prokudin-Gorskii produced outstanding work with a tricolor camera, his printed reproductions were sorely lacking in luminosity. The cost, complexity, and rarity of tricolor cameras kept this technological breakthrough from becoming anything more than a fad that could not supply publishers with the quantity of images they needed. There was simply no incentive for most publishers to change production methods.
Tricolor Gravure: While this photo-based image has all the appearances of being hand colored with an RGB pallet, or at least having the color placed in by a retoucher, the detail below shows it is definitely a process print made with a palette of light blue, yellow, and red.
The subtractive primary colors act like filters that absorb their complementary colors of red, green, and blue which compose white light. An object that absorbs (subtracts) one complementary color reflects the combination of the other two back. Ink that absorbs red reflects back blue and green, which creates the perception of cyan in the eye. When blue is absorbed green and red reflect back to form yellow, and the absorption of green reflects yellow and blue creating magenta. Thus when red, green, or blue needs to be subtracted from the additive color mix, its complimentary is printed instead for cyan will absorb red, yellow will absorb blue, and magenta will absorb green. To create additive primaries a combination of two subtractive primaries are printed. As cyan and magenta will absorb their complimentary red and green the color blue is reflected back to the eye. In this same way cyan and yellow make green, magenta and yellow make red, and the combination of cyan, yellow, and magenta absorb all colors to produce black.
Tricolor Rosette: This detail displays the typical rosette pattern found in early tricolor printing. It has been created by rotating of halftones of red, yellow, and blue 30 degrees from each other.
The three different ways that colors mix must be considered when trying to understand why printers chose particular palettes to work with. Subtractive color mixing is good in theory because it is a concept that works with pure nonexistent colors, but when dealing with physical pigmented inks in the real world, optical color mixing proved much more difficult to achieve. While we have come a long way in producing better colorants since the turn of the 20th century, there are no pigments or dyes that perfectly match any set of ideal primaries either back then or now. Without a perfect set of primaries, the full gamut they should theoretically produce through optical mixing is impossible to achieve. Constrained by the limited range of inks available, no consensus could be formed in these early years over what colors should be used as primaries. RGB became the standard for hand coloring, and while also used by some printers most stayed with the traditional combination of red, yellow, and blue (RYB), though often to imitate the RGB palette. The CYMK process colors that we have come to know, did not begin to become an industry standard until 1934.
Tricolor Line Block: This lithographic postcard from 1905 was printed with only three plates inked in yellow, red, and blue. Dr. Adolph Miethie, a pioneer of tricolor photography is given credit for the way that natural color is achieved.
Pigments do not all react the same when made into ink. Some of those used in lithography are opaque but most are semi-transparent. This allows for the mixing of hues by printing one semi-transparent layer of colored ink over another. There is no actual mixing of pigment as fresh ink is always printed over a layer that has dried, but the subtractive properties of each will combine. Many printers used transparency to create a larger color gamut, even when working in chromolithography that already started with a substantially large palette. A medium to dark blue was used on many early tricolor postcards, but printers began shifting toward a light blue when they saw its potential. Not only did this color produce a better looking sky than when a darker blue and white were optically mixed, it could also be printed over yellow to produce green. This eliminated the need to add green ink to the pallet while the yellow could also be used as a local color or for more layered mixing. As time went on both a light and a dark blue were sometimes printed on a single card to take advantage of the differing qualities that each provided. Printers for the most part payed more attention to how color inks behaved that to how color mixed in theory.
Artists may freely mix colors as they work but printers need to be sure that they don’t run out of a specified color ink during a press run. Consistent stock must remain on hand not just for one job but to also form the base for the proper color separation of printing plates for future jobs. The mixing of colors was already a tricky business because any new color formed was more a matter of how pigments chemically reacted with one another than the way wavelengths of light combine. The physical mixing of colored inks is something that has to be learned by trail and error for no theory can provide accurate guidelines. Some colors such as orange or purple that do not mixed very well with optical blending can be added to an image through spot printing. These or any other spot colors are rarely mixed, but used straight from a container as manufactured so that unpredictable results can be averted.
Tricolor Lithograph: Two of the three colors on this early postcard are closer to red and blue than they are to magenta and cyan. When these deeper values are overprinted they create a near black and hold the image together without the need of a fourth black key plate.
Tticolor Rosette: The black or rather near black in this true tricolor rosette pattern has been created solely by the overlapping of red, yellow, and blue dots.
Tticolor Rosette with Black: Both of these tricolor patterns of red, yellow, and blue has a black halftone added to it. In the detail above the typical rosette pattern is still formed, while in the detail below the RYB colors have been printed as chain dots, which disrupt the rosette but creates a stronger optical tint that softens the image.
As new colorants were introduced to the market, the printer’s palette started to grow closer to the CYM ideal, but as they began to print lighter, the result when overlapped was a noticeable muddy brown or purple instead of anything approaching black. The use of a black plate was now no longer a choice; it became a necessity to prevent soft looking images. When inks closely resembling a CYM palette were finally developed in 1934, they became the industry standard but this meant that using a fourth plate to hold black ink was almost mandatory. While this extra plate seeming required the use of more ink, less color ink was needed since multiple hues no longer had to overlap to produce dark tones. Most postcards from this point on were produced in a CYMK palette with black being abbreviated with a K for Key to differentiated it from B for Blue.
Tricolor Lithograph: Early attempts to render views through tricolor printing often resulted in dull looking images. While the RYB palette was less than ideal to create natural color images, it could still produce a bright gamut when reproducing illustration.
Tricolor Line Block: Instead of adding black to this Russian postcard, two different blues were used. The lighter blue assumes the role of cyan in the traditional tricolor mix while the darker blue substitutes for black as seen in the detail below. A sharp image is still maintained while a color cast is added.
Line Rotation: These two patterns were created through the overlay of halftones in the tricolor printing process. The pattern above consists of chain dots that have grown so long that the chaining lines they form are more obvious than the rosette pattern. The dots below were laid down with an early version of the Ives line screen. While neither series of line rotations creates the perfect rosette pattern we now associate with process printing, they are still both adequate solutions in preventing the formation of noticeable interference patterns.
The secret in avoiding interference patterns in tricolor printing is by laying the three overlapping color halftones at angles with exactly 30 degrees of difference between them. Just a one-degree deviation from this formula can create noticeable interference. The final flower-like design that results from this three color rotation is known as a rosette pattern. If printed small enough it has no repeat discernible to the eye, and as a result it creates the illusion of continuous tone. The obvious problem inherent in this method is that a maximum of only three colors can be used before the angles of rotation repeat themselves. This posed no problem when the only colors used were the three primary hues, but when black needed to be added to the mix there was no room for it in the rotation. Since yellow creates the least amount of contrast due to its very light value, it was found that it could be only rotated at a 15 degree angle without any adverse effect allowing black to take its original position.
Line Rotation: This illustration depicts the standard 30-degree angles that the cyan, magenta, and black halftone patterns must be rotated to form a perfect rosette in process printing. Note that the yellow is only rotated 15-degrees with little adverse effect. The slightest deviation from this model runs the risk of creating unsightly moire patterns.
The angles of displacement for positioning screen patterns were not at all arbitrary. The human eye is most sensitive to vertical and horizontal lines so the screen that carries the most readable pattern of black is positioned at 45-degrees, and the least noticeable color yellow is positioned at 90-degrees. The remaining magenta is positioned at 75-degrees, and cyan at 105-degrees. While this has become the preferred formula for placing color within the printing trades, colors were positioned differently when only three colors were used, and differently again if needed to accommodate an unusual number of colors or to create certain effects.
Color Halftone: This very unusual line block postcard from 1907 was printed with an RYB pallet, but all three halftone plates have the same 45-degree angle of rotation. Moiré patterns were averted by printing all the colors on overlapping lines like a screen. While this solution has created a soft look, it also gives the uncomfortable illusion that the colors have been printed a bit off register.
Color Halftone: While the proper degrees of halftone rotation were exactly prescribed, there were those who deviated from it for effect. On this linen postcard both the red and black dots are on the same 45-degree rotation. The pattern seen in the detail below falls somewhere in between a pleasing rosette and a distracting moiré, but it works here in relation to the drawn illustration as if it were simulating a rough paper texture.
Dot Gain: When halftone dots grow very large in color printing (dot gain) they can completely cover the paper’s surface and nearly obliterate the tell tale rosette pattern. This characteristic has always been true as we can see in the detail above from a card made in the 1920’s, but dot gain is even more prevalent in offset printing as seen in the detail below from a card printed in the 1990’s. Offset printing always creates bigger dots because the ink spreads outward when transferred off of a soft rubber roller.
Chain Dots: Depending on the type of line screen used to produce the halftone, the printed dots can assume various shapes. The elliptical pattern would become very popular in process printing, especially when used in conjunction with offset printing methods as seen in the detail below. As the oblong dots grow longer in one direction they form chaining-lines. They can also be made to grow in two directions to create a screen-like pattern. These types of patterns can sometimes overwhelm the inherent rosette contained within.
Spot Color: The gold spot color on this postcard is used for both stylistic and evocative effects. Its delicate application goes far beyond presenting an additional color to create the illusion of gold embroidery on a lace dress as seen in the detail below.