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Digital Printing Techniques
Impact printing refers to those methods by which the final image is physically transferred to paper by means of a striking mechanism. This process is a direct outgrowth of letterpress where inked cast type was pressed into paper. All the basic principles are the same; they are only put together in a different manner, and without the need of a bulky press. The earliest impact devices were typewriters that were powered by hand and whose speed was determined by the skill of the typist. These machines spit out print much faster than what could be written by hand, but not nearly as fast as a printing press. Despite their speed and limited printing abilities they would become indispensable to the business world. It is only natural that digital technology was eventually adapted to this form of printing. This fusion of old and new proved to be largely an interim measure, for as technology quickly advanced, the efficiency of these mechanical devices was outpaced by newer forms of printing. While largely replaced by non-impact printers they continue to fill particular needs.
While there were many early patents for prototypes, the first commercially made typewriter came out in 1870, and most brands were fairly standardized by 1910. Though still in use, the market for these machines has dramatically dwindled as the public turns toward digital desktop technologies. Habits however die hard and the current computer keyboard is still based on the strange standard configuration of the English language typewriter. It has been suggested that the QWERTY keyboard layout was designed to slow down typing speed because the metal typebars (keys) would tangle and jam if the typist worked too fast. While typewriters were not used to manufacture postcards, they were used to place messages on them, especially when sent out from businesses and institutions. In this sense they could be considered a final step in their production in the same way that letterpress captions were often added to lithographic cards. Typewriter-like type fonts are still alluded to on postcards printed in offset lithography.
Typewriter: This chromolithographic postcard from 1907 was used to advertise Yost typewriters. Its back gives a good example of the different ways type was printed. The top line in the detail below is printed with cast type, and the shaky letters in the middle line are printed in line block to imitate typewriting. At this time there was no cast type that could produce facsimile typewriter fonts so they were drawn onto a line block plate and etched. The fuzzy letters on the bottom line were typed onto the card with an actual typewriter. The excess ink from the fresh ribbon has bled into the paper giving the font a soft edge.
Typewritten Card: This handmade postcard is nothing more than a stiff sheet of brown paper with a photograph tipped in. A typewriter was used to place a caption on it. Typewriters were often used with handmade cards; perhaps to make their rough character look more formal.
Dot Matrix Printing
Dot Matrix Print: In this detail we can see how the many dots printed by a dot matrix printer combine to create a font. While elaborate fonts could be created by a dot matrix printer, most commercial applications use the most rudimentary form of lettering possible.
In Electro-photography, electrical charges are manipulated on a drum or roller in direct relation to a scanned image. Powdered pigments or liquid dyes that are made to physically correspond to these variances of static are then transferred to a substrate and fused to it through heat. This process based on the photo electric effect, discovered in the late 19th century would be greatly enhanced with the introduction of digital technology. While not designed to compete with the high capacity runs of commercial printing used to make most postcards, these methods greatly aided the limited production needs of desktop publishing. They would also help inspire new art forms that incorporated postcards such as mail-art, copy-art, and scanography. The speed of these new types of printing devices would not only increase over time, parts of this technology would eventually be applied to more standard methods of printing such as offset lithography and gravure.
With no set up time as with printing presses, there is no need for minimum press runs when using this process. The lack of prepress work involving film transparencies also made this method fast and efficient, but it isn’t without its problems. Electrostatic printing with dry toner can only produce solid blacks and is poor in producing optical grey. Even though photomultipliers are sensitive enough to register a single photon, the particles in the toner are much larger and they produce fuzzy edges when attracted by static causing a significant loss in detail as small white spaces fill in. The type of paper that can be used is also a limiting factor because the short bursts of heat that bond the pigment and resin to it cannot easily penetrate heavy stock. When this happens the pigment will not properly melt causing it to smudge or completely wipe off the paper. The amount of additional heat that can be applied is also limited for too much will burn the paper. As it is, the heat buildup in these machines can be excessive preventing their continual use.
Photocopy: In this detail of a photocopied image we can see the typical high contrast and the fuzzy edges it produces.
Laser Printing: While a laser copier can produce a sharper image than a photocopier, it still has problems rendering optical grey. In the detail below we can easily see the typical line patterns formed from the back and forth laser scan because the dark grey was broken down into large irregular marks of black or white instead of fine tone.
For many years laser copiers were used to directly scan reflective material or receive a projected image from a transparency and then print out a copy. When it became possible for images to be manipulated by computer software or be entirely generated by them with no need for a physical original, a new model of desktop publishing emerged. As images could easily be transferred digitally from one device to another, separate devices more suitable for either scanning or printing were developed. While laser printers are not generally used in the commercial printing of postcards they are sometimes employed for low volume work. They have also inspired a new type of art card under the guise of scanography.
Color Laser Printing
Color Laser Print; The dots on this laser print from 1980 were printed in a pattern resembling a halftone screen. In the detail below we can see that printing each color almost atop one another in the same 45-degree rotation averted moiré patterns, but it also seems to have caused localized color casts.
Color Laser Printing: While the individual dots on this laser printed postcard from 2006 are too small to see even under significant magnification, the laser printer has left behind banding as a result of the linear scanning process. Banding may not be visible on the card but it can be easily seen in the detail below. These types of lines were even more apparent on earlier prints as seen on the detail from a card printed in 1980 further below.
Inkjet Printing: The random dot pattern created by an early inkjet printer is clearly visible on this detail because of the large amount of white paper left untouched for optical tonal blending.
The introduction of digital technology and the growth of desktop publishing led to new forms of inkjet printing. One type is thermal inkjet printing invented by Ichiro Endo in 1977. Here water based ink held in small chambers within a cartridge are shot out of its head in droplets from the pressure created by heat generated bubbles (bubble jet). The other method of inkjet printing utilizes the piezoelectric effect. When an electric current is applied to the piezo crystals that sit at the back of each chamber of an ink cartridge, it begins to vibrate and the pressure formed forces the ink out of its head in small droplets. A wide variety of inks can be used in conjunction with Piezo printers. In all these printers the ink cartridge moves back and forth across the paper while the paper is rotated under the nozzles of the cartridge’s head so that each line printed will blend seamlessly into the next. The release of ink is directed digitally by a computer, which also determines the number of dots per inch (dpi) that will print. Inkjet printers can be instructed to print with dpi set at different frequencies but this number is still limited by the model of the machine.
Inkjet Printing: This image was printed on a postcard sized sheet of coated paper with an inkjet printer. There is no way of telling how many cards were produced but this method is not typically used for high volume work. Vibrant colors can be produced with inkjet printing but their dye based inks quickly fade. More archival inks have been developed for use on specialized printers that have approximately the same life of color photographs.
The manufacturers of inkjet printers usually produced their own line of inkjet recording papers with a porous ink-receiving layer specifically designed to be receptive to their own brand of ink. While this paper was ideal for printing, improvements in overall paper production allowed a variety of non-brand products to produce adequate results. Competition then led to the production of specialty papers of varying quality and texture. Among these were inkjet paper issued in postcard size. While in some sense this is similar to Kodak’s early card stock photo paper issued with printed postcard backs, this newer paper has neither the printed back nor the weight of most real photo cards. Printed postcards are also usually varnished to help them survive their journey through the mail, but these inkjet cards on glossy stock have no coating and they tend to easily smudge. The type of ink used can also greatly affect the quality of these cards. While new inkjet printers have been designed to use inks with greater archival properties, the vast majority of printers use dye based inks that are highly fugitive. Even though inkjet postcards can be printed in small quantities at home, their problematic qualities have rendered them more of a novelty than a practical postcard.
Inkjet Printing: This image is an inkjet reproduction of a hybrid postcard originally printed in collotype over lithographic dots. While no halftone was employed in the original, we can see in the detail below how the scanner translated each of the original dots into a multitude of smaller color dots. There is also a very noticeable grid pattern that is not in the original but was formed by the way the digital information is captured and stored.
It was eventually realized that there was no need for digital scanners to reproduce the exact patterns of halftone screens that create changes in value by varying the dot size within a rigid frequency. A new frequency modulated screening method known as stochastic printing was developed where the small dots set by the imagesetter do not change in size to create optical tones, it is their density that is used to create subtle shifts in both value and hue. While stochastic screens retain the same overall balance between black and white as with real halftones, they exchange many smaller randomly placed dots for one normal sized halftone dot. This almost invisible texture creates very smooth and nuanced transitions while at the same time rendering much finer detail. Without a screen pattern to contend with, there is no need for line rotation, which in turn allows any number of colors to be used without fear of creating interference patterns.
Inkjet Screens: In these two details from inkjet prints we can see that even when color ink is laid down in a random pattern that they can produce very different results. The oldest pattern seen above will be perceived as a color while the pattern below will appear as black & white to the eye with only a slight color cast on the full image.
Stochastic Screens: These two details were both made with a stochastic screen. The one above will optically read as an even tone when viewed at full size while it will be possible to read individual colors in the one below due to the massing of dots. The best printers can lay down over eight million dots within a square inch to create the most subtle of transitions.
Dithering: When the postcard above was scanned, the rosette pattern on its printed surface was recorded as digital information, and when this same information is then viewed on a monitor or in printed form, it is rendered in lines. When these two different and distinct patterns are overlapped they create an unwanted third pattern as seen above. By adding another random pattern of noise through dithering, the previously observed moir’ will no longer be perceivable as a pattern as seen below. (NOTE: The interference pattern on the card above will appear differently depending on the size it is viewed at on your monitor.)
Black & White Inkjet Print: To create better tonal range with smooth transitions, an inkjet printer has reproduced this black & white image with all CYMK colors. The outcome is an image that only has a slight monochromatic cast, though in the detail below we can better see the full range of color dots that make up the image.
Black & White Inkjet Print: As this black & white picture was being printed, the printer ran low on black and then cyan ink, which suddenly created a strong disturbing color cast by revealing the color mix. Without a full CYMK palette, the gamut needed to produce a neutral image cannot be achieved and there will be a dramatic shift in the color balance.
Digital Imitation: The printing from the back of this pre World War One card shown above should be in a solid letterpress tone but it is made up of a multi-color dot matrix from a modern inkjet printer. The brown age marks also comprise of small dots indicating that they have also been printed onto the card. On the detail below the dot matrix is clearly visible while the detail further below from an antique postcard exhibits a true solid tone and finer details.
Expanded Inkjet Pallets
Inkjet Print: This copy of a postcard from 1912 was made with a seven-color inkjet printer. To create softer tonal gradations the printer has added in color where none existed on the original causing its surface to shimmer as seen in the detail below. By doing so it has also lost definition when compared to the original collotype it reproduces seen further below.
The rise of new digital technology has created problems in definition. The same inkjet printer now used to print a digital photograph is also used to produce original art work created with computer software. The color pie chart printed with an inkjet printer for an office report can be materially identical to a print presented in a gallery as fine art, only the intent is different. Various terms have sprung up over the years to denote distinctions where none really exist. Today all of these variations are slowly coming to be referred to as digital prints regardless of their origins.
DIGITAL ROTERY PRINTING
There are few of us today who are not familiar with digital printing, but it is usually the laser and inkjet printers on our desktops that first come to mind. Commercial printing is still often surrounded by romantic notions of an inky pressman feeding paper into a chugging press. While large rotary type presses still dominate the printing industry; the way that plates are now made for them has drastically been altered in this digital world.
Electromechanical Engraving (EME)
Electromechanical Engraving: Even at very high resolution it is difficult to make out the individual characteristics of the dots printed by a rotogravure plate engraved with an electric stylus. The dots however generally appear soft and create tone both through their depth and through optical blending. The ink on many of these dots has been wiped clean from their centers producing tell tale O shapes.
While creating a gravure plate with an electronically directed stylus is much more precise than etching a cylinder in acid, it is a long time consuming process. From this problem grew a new way of incising plates where a laser beam would cut cells of varying depth and width directly into the cylinder at 1/10 of the old speed. The increased depth also increased print quality as the ink tends to stay inside the inkwells. The original image is scanned and digitized just like in electromechanical engraving, and this information then guides the laser beam in a precise manner. The reflective surface of copper however is problematic, so these cylinders are usually first coated in plastic. Once the image has been transferred, it is then electroplated with chrome. This added protection increases surface strength allowing for consistent press runs of over a million. Once a run is complete the image on cylinder can be stripped off and a fresh coating applied.
Laser Gravure: On the detail from this color rotogravure cut by a laser, we can see that the dots tend to take on an oval shape and they loose their distinction when printed near or atop each other. To the unaided eye these marks will blend into a continuous tone.
As the printing industry incorporates more and more digital technology, it has become difficult for shops to hang onto older methods of producing prints regardless of their quality. Most photographs today are digital, which means that the step of scanning an image can often be eliminated as all visual information can be passes around electromagnetically between camera, computer, and press. Computer to plate technology (CTP) has not just improved on production time; it has replaced the need to use toxic chemicals in the processing of film. While it may be argued that the image integrity of the final print is closer to the original due to the fewer intermediary steps needed in production, a digital original does not come close to capturing the subtleties of color and the sharpness of detail that is captured by high quality film. These nuances however are often not perceivable when printing small scale items such as postcards. The ability to manipulate and transfer visual information at an unprecedented level has tipped the scales.
Digital Offset Printing (Indigo Printing)
Indigo Print: This card was printed in red, yellow, blue, and black. The red and blue have been laid down in rotated patterns while the black dots are more randomly placed. The dots are large and fuzzy, more like those found in offset lithography than inkjet printing.
Indigo or Offset: One result of digital technology is that different printing techniques have become more difficult to differentiate. Even under magnification an indigo print looks little different from offset lithography as the color dots of each spread out from their transfer off a soft roller.
While clients may have always held very precise ideas concerning the postcards they want to have printed, the typesetting and layout was traditionally carried out by prepress workers within a printing firm. This type of work became easier and more efficient with the introduction of digital technology, but as the use of computers and image manipulating software became more widespread, many customers grew capable of doing this preliminary work at home. Jobs are now often submitted to printers digitally burned into compact discs or even via email (web to print). Some printers have even set up interactive programs on their own Internet websites to make it easy for clients to do this work from their office or home computers. In many cases prepress workers still have to process this information into a form their shop can print with, but as the industry shifts more and more towards digital imaging it has become possible to transmit an image straight from a customers desktop directly onto a printing plate from any distance. The worker who places an order in a box to mail it may be the only person to touch a postcard before it reaches the customer, and even this step is being replaced by robotics.
THE INTERNET AND CYBERSPACE
At some point after the inception of the Internet in 1971, images with notes attached to them started being sent through the Ethernet, and by 1996 it became a popular practice to send emails that resemble paper postcards. Ever since there have been a number of online companies that offer copies of antique postcards alongside original modern designs that can be sent out through email. Designers have even taken advantage of this new medium to create cards that talk and some that are even animated. Since these eCards have no physical reality to them other than their magnetic energy floating out in cyberspace, any further discussion of them goes beyond the scope of this guide to printing techniques.
Binary Code: Is this the face of the new postcard?
Despite that no postage is required, and that they can be made at home, eCards have not replaced snail-mail cards, at least not yet. It is foolish to consider any one technology as the end of the line, for as we have seen on these pages that many widespread methods of printing such as wood engraving, chromolithography and letterpress all fell from their positions of dominance. There is still a great probability that new amazing analog printing techniques are yet to be posted to this guide.