METROPOSTCARD.COM GUIDE TO PRINTING TECHNIQUES 2
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Photography and the Black Arts


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GRAVURE


Usage of the term gravure is often commonly applied to any photo-intaglio technique but it specifically makes reference to prints of fine grain made through the photogravure or rotogravure process. Gravure is an old technique and it could be argued that the very first photographs made in the form of heliographs were actually gravures. The gravure process has continued to evolve since its inception and is still widely used in commercial printing today. It was used in the production of many postcards but it was a pricey technique that limited its application. Most higher end monochrome postcards printed in Europe between the two world wars were produced through rotogravure.

Photoglyphic Engraving
In the 1820’s the printer Nicéphore Niépce saturated a printed engraving with wax to make it translucent so that he could expose it like a negative to a copper plate made light sensitive with a coating of bitumen. The result was the heliograph, the first known permanent photomechanical transfer, but the various problems that continued to be encountered always prohibited its commercial use. His experiments however caught the eye of the painter Louis Daguerre and they formed a partnership to carry the possibilities of this technique further. Niépce’s death in 1833 cut this collaboration short, and it took four more years for Daguerre to invent the daguerreotype. He planed to keep this process a trade secret but just two years later after his studio burnt down, he was forced to sell the rights to the French government out of desperation. The making of a daguerreotype begins by photosensitizing a silver plate with iodide of silver, and immediately after exposure to light it would be passed over vapor from a hot bath of mercury. The mercury would only adhere to the iodide of silver in proportion to where it received the most light, and then the remaining emulsion was washed away in a bath of salt water. The resulting low relief caused minute shadows when light fell across it at an angle, and this replicated the appearance of the scene shot through the camera’s lens. While many improvements were made to this process, daguerreotypes could only produced a one of a kind image that mirrored the original subject, and its surface remained so delicate that it could not be touched. Its use ended in the 1860’s while in competition with photography but its implications would live on.

W.H. Fox Talbot continued the experiments that Thomas Wedgewood began in 1802 in which he captured an image on photosensitized paper; but it was in 1835 that Talbot finally found a way to permanently fix this transferred image so it would not fade away under light. While this marked the beginning of true photography, Talbot also sought out ways to incorporate the photographic process into printing. By 1852 he began experimenting with gelatin emulsions (fish glue) for their potential use as an acid resist in etching photographic images onto metal plates. Six years later he realized he could achieve richer tones by first coating the polished metal substrate with a dusting of gum copal powder, which was melted onto the plate before photosensitizing it with gelatin. The copal acted as an acid resist but one with a delicate irregular grain. It also guarantied that a fine texture would be bitten into the plate even if too much of the emulsion was washed off.



PHOTOGRAVURE (Hand Gravure)

Printers had seen potential in daguerreotypes and by the 1840’s some were being etched and engraved upon to strengthen the image for use as a printing substrate, but the plate’s surface remained very delicate and this method only saw limited use. Eventually the photoglyphic engraving process as used by Talbot evolved into photogravure (called heliogravure in Europe) by substituting the same fine resin powder as used in aquatints for copal. Once the rosin was melted onto a plate’s surface to create a random dot pattern, a clear photosensitive dichromate gelatin emulsion is applied. When dry, the plate is then exposed to light through a positive transparency. Areas where light hits the gelatin are hardened to form an additional acid resist, and the remaining water soluble gelatin is then washed away. This will leave some areas of the plate’s surface around the baked on rosin crystals completely exposed, while others areas will retain a thin gelatin coating in proportion to its exposure to light, which is determined by the density of the transparency that covered it. The plate is then heated at a higher temperature making its surface very hard, and the remaining resist is sometimes dyed a dark hue to better observe the image against the exposed metal. When placed in successive acid baths of decreasing strength, the metal will first dissolve in the exposed areas between the rosin dots. The thinner areas of gelatin will eventually be eaten away in proportion to its thickness, slowly revealing more bare metal to the acid. Areas that have less contact time with the acid will not etch as deeply as those that do, and these shallow wells will hold less ink producing lighter tones when printed. Since the plate is slowly etched down, the final print can hold very subtle gradations.

Photogravure produces thousands of irregular ink cells in varying depths that can merge into a subtle continuous toned image with very rich blacks. In addition the printing plate is also very durable, able to yield sixty-thousand impressions. Though the results obtained by this process are of a higher quality than many other printing methods, its complexity makes it relatively more expensive and some printers sought ways to reduce cost. The Jaffe Brothers in Vienna expanded upon Talbot’s photographic veil in 1877 by using millers gauze to break up the image while being photomechanically transferred. Other techniques such as the stagmatype (spitzertype) introduced in 1866 featured a gum grain placed within the photosensitive gelatin emulsion. All the alternatives faired worse in the marketplace, so despite the cost photogravures remained in production up into the 1930’s, but only to produce higher end postcards. Most printers however eventually switched to the more expedient process of rotogravure, and only a handful of fine printers use this photogravure today.

Postcard

Photogravure: The tonalities produced through photogravure on this early postcard appear almost continuous and unbroken. Even under high magnification the texture is so tight that it makes the process difficult to identify. The occasional small white dots characteristic of the underlying aquatint are the only giveaway visible in the detail below.

Postcard Detail

The printing plates used with photogravure and collotype both hold ink in the spaces formed between particles of resist that leave their own distinctive patterns on the final print. They show up as white dots on photogravure from where the grains of aquatint once sat on the plate preventing it from biting in the acid bath. The small white marks on collotypes tend to look wormy as their shape is determined by the curdling of light hardened reticulated gelatin emulsion. A further distinction between these two processes is in their tonal structure. On close examination the ink on a photogravure sits as a crust atop a paper’s surface creating rich flat blacks while the thiner ink of a collotype produces a good range of grey but poor dark tones. While these are the major differences to look for in making a determination of technique, there is a substantial problem, these descriptions do not always hold true. Many different patterns can be created with aquatint. If the rosin crystals are heated too long or over too high a heat they can melt into each other creating chain like patterns that are wormy like curdled gelatin. The various practitioners of collotype had many trade secrets that often rendered the texture of one different from another. Sometimes the white marks produced are so small they have no distinctive shape at all and cannot be differentiated from a fine aquatint. Some of these printers also managed to push the collotype process into producing real blacks while light subject matter in photogravure may be etched so lightly that only a trace of ink is printed.

Postcard

Photogravure: Photogravure’s tendency to render soft tones works against it on this postcard. The atmosphere of this distant landscape provides little contrast and few details to pick up on causing the image rendered to lose coherence. This effect is further exaggerated by the uncoated paper it is printed on, which softens the edges of objects by absorbing ink.


Duogravure
Duogravures are produced through procedures borrowed from the making of lithographic duographs except that these images were etched as gravure into metal plates. The process starts by making two separate processing transparencies from the same photograph with one exposed to capture medium to light tones, and the other for darker values. Each is then photomechanically transferred and etched in gravure. When one plate inked in a light neutral color and another in a darker color they produced a much richer looking image when printed together than could be achieved from black & white alone. While any colors could be used, the prevailing palette was fairly neutral, often differing values of the same hue. This process became very popular in the 1930’s for the fine reproduction of photographs, but it was mostly used on European postcards.

Postcard

Duogravure: At first glance this postcard in photogravure appears to be printed in a deep brown. The detail below reveals that a lighter brown has been printed under the black from a separate plate to carry the lighter values and give the entire image a pleasing warm cast.

Postcard

Color Photogravure
As with all intaglio techniques, photogravures could be printed in color by employing multiple plates, one for each individual color that was desired. The color plates were often more lightly etched than they normally would be so that no one color would overwhelm another when these rather opaque inks were united into a single print. Completely solid color fields were rarely printed as all areas were usually made up of a multitude of countless little markings. A tricolor intaglio printing method employing mezzotint had been patented by the German printer, Jakob Chrisoffel Le Blon in 1717, but it did perform well as a commercial endeavor. The methodology was revised in the form of color gravure in the 1880’s, but its commercial applications remained limited due to registration problems and high cost.

Crayon Gravure
Crayon gravure is not a printing technique but a style that reproduces the texture of crayon, which in most cases is synonymous for pastel. These are basically color photogravures that use a very coarse grain when making the photomechanical transfer of the illustration onto a printing plate. This texture further enhances the illusion of a drawing on rough paper as its white dots have a similar appearance to the recessed areas of the paper’s surface that do not pick up pigment when drawing. This process was never widely used in the printing trades, probably due to cost, but it can be found on postcards made well into the 20th century long after most other uses for photogravure had ended.

Postcard

Crayon Gravure: This roadside postcard from the 1960’s reproduces a drawing made in pastel or color pencil. It is printed with the same CYMK pallet used in process printing but it looks richer because it is printed in gravure. The loose nature of the drawing leaves much white space on the paper, which in turn overwhelms any printed texture making the technique difficult to discern. The darkest areas found in the lettering are revealing; they have very coarse edges and a body filled with small white dots typical of photogravure.



ROTOGRAVURE (Machine Gravure)

Photogravure had been used in commercial printing since the paper fed press was developed in 1863, but there was no way to adapt the process to fast rotary presses because it was impossible to expose a large metal cylinder to a photograph through a halftone screen. In 1864, J. W. Swan discovered a way of transferring an image onto a metal plate by using a photosensitive gelatin tissue, and in 1879, Karl Klic replaced Talbot’s first step of aquatinting a plate by infusing the gelatin tissue itself with a dot pattern. This new tissue was not only able to produce an attractive random grain along with fine detail, Klic’s method provided the most consistent results and it soon became the most widely used. Just as important, the use of gelatin tissue would allow gravure to migrate to the rotary press because it could easily be exposed anywhere and later wrapped around a copper coated cylinder. Once adhered, the cylinder could then be etched by rotating it through a tray of acid. Rather than patent and license his invention, Klic hoped his Rembrandt Intaglio Printing Company could keep a monopoly on the process; but when an apprentice left for America he took the trade secret with him. By 1904 rotogravure was in widespread use and producing countless postcards. While rotogravure was designed for use on a rotary press these plates were sometimes printed on flatbed hand presses.

Postcard

Rotary Press: Pictured here is a small but modern electric rotary press produced by the Swiss firm, A.G.Brown, Bovery & Co. The card itself is printed in rotogravure.


Postcard

Rotogravure: The postcard above is typical of rotogravure printing. None of its ink cells are visible to the naked eye; instead we are provided with a wide tonal range, smooth transitions, and deep velvety blacks with a matte finish. This process, so adept are reproducing photographs was also capable of reproducing artwork with the same fine qualities as seen on the card below.

Postcard

In 1908 two textile printers, Eduard Mertens and Ernst Rolffs took rotogravure’s development much further. Rolffs developed a method by which a gelatin tissue is double exposed, first to create a solid crossline screen pattern across the entire surface of the cylinder to act as an acid resist. This screen will not print but remain white while allowing the square cells between them to be further exposed. The second exposure is then made with the transparency that holds the image, which causes the square cells to harden in proportion to the amount of light filtering through the transparency. The tissue is then adhered to a cylinder and the soft areas are washed out with water leaving a hard acid resist behind. The acid bath it is rolled through will incise a continuous toned image into its surface between the screened lines by creating small ink cells of substantial but varying depth. The deeper depressions will transfer more ink to the printing surface creating darker areas while the shallow inkwells that tend to only capture ink around their edges will print lighter. The screen pattern completely disappears in the non-image areas of the cylinder that do not receive an etch. In dark areas the fine lines of the screen pattern that were not etched will leave behind a faint white grid around the wells. These lines are too small to be visible to the naked eye especially in areas of dense blacks where the ink is pulled out of the wells to produce a heavy plate tone.

Postcard Detail

Rotogravure: These two details reveal the grid like cell patterns found in rotogravure. While the regular pattern above was created with a typical crosshatched line screen, the more irregular pattern below demonstrates that there was more than one type of screen type for printers to choose from. While patterns other than crosshatching are less visible, they were more difficult to make and saw less use.

Postcard Detail

During printing, the etched screen cylinder revolves through an ink fountain where it is coated with fluid ink. Eduard Mertens invented a wiping blade (doctor blade) that clears ink away from surface areas of the cylinder while leaving ink safely in the depressions protected by the crossline grid. When paper passes between the etched cylinder and an impression cylinder, its soft rubber covering pushes the paper into the steep incised ink cells and the image is transferred onto the paper. This mechanical inking process sped up printing time considerably and it replaced the old hand inking and wiping methods within two years. The expense involved in making cylinders often caused them to be reserved for very long runs on web-fed presses. For pressruns of a million or more, the cylinders are plated with chromium to provide extra durability. This process was patented in 1910 and was picked up soon after by commercial printers. While these new changes to the gravure process made it much more commercially viable, it was not typically used by American printers for postcard production. It did however gain great popularity in Europe where many monochromatic cards were produced by this method. While designed for use on rotary presses, rotogravure postcards were usually made on sheet-fed presses.

Postcard Detail

Rotogravure: Since the ink used in rotogravure is transferred out from deep wells in the plate’s surface it can lay thickly on a paper’s surface once printed. This often forms a rich even tone, which can make this medium difficult to discern. Evidence of the technique can best be found in the inky crust that builds up in the darkest areas while the inherent grid pattern is easiest to observe in the lighter tones that carry less ink. While the detail below seems to reveal white boxes in a dark grid, this is only an illusion. The ink is actually only hugging two edges within each square inkwell, and as it spills out over a large surface area, it forms a screen-like pattern.

Postcard Detail

Postcard

Rotogravure: This postcard from 1915 captures so much detail that it can be mistaken for a collotype even though its rich darks are closer to gravure. On close examination the only grain seems to be that of that caused by the papers fibers. It is very easy to mistake this card for a photogravure for it is only in a few of the white details as seen below that the faint pattern of a rotogravure plate shows up.

Postcard Detail

Toward the end of the 20th century, the use of gelatin tissue in the rotogravure process began being replaced with a high contrast photopolymer emulsion that was usually sprayed directly onto the copper plated cylinder. This not only allowed printed images to be made with higher resolution, it dramatically speed up production time. Its widespread use however has been curtailed by the introduction of electromechanical engraving based on digital technology.

Monochromes
The simplest way of producing a postcard is to print it in a single hue. Though most monochromatic postcards were printed in black & white, they can also be found in many shades of blue, green, sepia or dark brown. It is these standard one color cards that are typically referred to monochromes. Since these colored inks were produced from common pigments, they could be manufactured in large quantities, which made them inexpensive to use. This allowed publishers to print monochrome cards at a similar cost to their black & white cousins while often charging a bit more for its unique coloration. Prints made from a single plate carry a lower density of ink than color prints made from multiple plates, which makes their details appear much sharper. This became a selling point for monochrome cards in a market that normally prefers color.

Postcard

Monochrome Rotoravure While the blue tones of this postcard image have some associations with a wintery landscape, there were no set rules that printers followed when matching color to subject matter on monochromes. It is not unusual to find the same image printed in different hues.


The audience for monochrome postcards was much larger in Europe than in the United States. This was at least in part due to preferential differences among customers. Most of the monotones popular in Europe were printed in a fine high quality gravure, which made them more expensive. Price was a more decisive factor in the United States, and cheeper lithographic postcards of varying quality were produced instead to meet consumer demand. Being the easiest to print, postcards of only one color have been used since their inception, though in postcard’s golden age, monochromes were just another minor variation to what was then available. Many of the monochromes that became common by the 1930’s were printed by less expensive means than gravure in efforts to drive down cost. After the introduction of cheep photochrome postcards, the monochrome postcard disappeared in relevant numbers.



COLOR ROTOGRAVURE

Intaglio had largely been an unpopular method for multiple plate color printing because the wet paper used would cause registration problems as it dried and shrank. The texture of gravure however was not nearly as deep as their line etched cousins so less pressure could be used when printing them. This meant that the paper need not be as pliable, so it was dampen less, which reduced shrinkage and improved registration. While many postcards were printed in color rotogravure, its complexities and expense kept it from gaining as wide an acceptance with printers as did lithography and line block.

Postcard

Color Rotogravure: When printing in color rotogravure, red, yellow, blue, and black is the standard palette instead of the usual CMYK process colors used in offset lithography. A separate cylinder is made for every color that is needed to print. In the detail below the typical square cells of rotogravure are still evident despite all the over printings of color ink.

Postcard Detail


Postcard

Color Rotogravure: While a black gravure key plate has no problem translating a photographic image, colors always seemed forced as if applied by hand, making the color gravure process more suitable for reproducing illustrations. This postcard from 1952 shows that publishers recognized the unique benefits of this look, and they continued to employ the process even when cheeper alternative printing methods were available. In the detail below it is obvious that the direction of the gravure cells have been rotated to closely imitate the rotation of dot screens used in process printing. The similar rosette created helps to hide the cells and eliminate unsightly interference patterns.

Postcard Detail


Postcard

Color Rotogravure: Even though the details below of this postcard pictured above lack high clarity, color rotogravure in the right hands could be used to create wonderfully subtle results. High resolution is not always needed because of the minds ability to extrapolate visual hints.

Postcard Detail


Postcard

Photo Rotogravure: The flatness of the colors on the postcard above would suggest it was made through lithography while it actually consists of rotogravure dots printed in a light red, yellow, and blue. Even though the dark blue printed as a solid gravure tone works as a key, it also displays a modern tendency to render images more abstractly through color fields rather than line. Here style trumps technique.



Postcard

Color Rotogravure: The darks in this early color rotogravure take on the typical solid crusty characteristics of most work in gravure, but the highlights are printed with such fine marks that the technique is almost indecipherable. The small ink wells have created a sharp clean image with fine detail. Note the effort made to make the card look as if it was printed with an RGB palette even when RYB colors was used.

Postcard Detail


Postcard

Color Rotogravure: Modern rotogravure is now capable of producing much richer color mixes. While the process as used here has not created the natural color that is often associated with photochromes, it has manage to remain competitive by producing a rich and enhanced color mix reminiscent of a hand colored photo. Technique is no longer affecting appearance as much as a desired look is determining technique. In the detail below the gridlines of the plate are clearly visible due to its large inkwells, which also help give the image a softer look.

Postcard Detail





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