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Halftones and Hybrids


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HALFTONE


The invention of the halftone process would radically change the way illustrations were reproduced in print. They were immediately put to use during the 1890’s drastically reducing the costs of commercial printing, which in turn made printed illustrations much more common. At the same time the technique of wood engraving had reached the point where production teams could work on separate pieces of a single picture and then reassemble them, greatly speeding up production time on this normally slow process. Although this method of cutting an introduction of photoengraving finally allowed images to accompany breaking news stories, it still required the skills of highly trained craftsmen to produce them, which kept costs high. Illustrations from halftones were cheap to reproduce; only $20 for a full page as opposed to $300 for a wood engraving. The writing was on the wall and many publishers who did not care for the look of halftones, and there was a lot not to like, used them anyway in order to stay competitive. By the time postcards had become popular, the use of wood engraving for commercial printing had already come to an end.

While these pages are primarily concerned with discussing technique, the great disruption that halftones had on society should be noted. Its sudden rise to dominance in the printing trades eliminated the jobs of countless highly skilled workers and new employees had to learn a whole new set of skills for which there were few teachers. There was also great debate over how halftones might transform society. By 1902 the Industrial Art League held its first national conference in Chicago to debate the implications of the crossroads that lay before them. Some felt this melding of technology and the arts into industrial art offered a great historical opportunity to expose the general public to high culture cloistered away in museums. Others however were fearful that the flood of imagery halftones would provide would only diminish aesthetic values, and efforts to please public taste would surround us with mediocrity. This debate over the proliferation of imagery in society still goes on and has taken on new concerns in the digital age.




Postcard

Halftones: The black & white postcard above is a typical example of what a halftone could render at the turn of the century. It suddenly allowed photographs to be easily turned into printed images, but this was not its only use. Through the use of halftones, images created in one medium could easily be transferred to another medium more suitable for commercial printing without losing its inherent visual characteristics. Below is a postcard dating from the 1950’s on which A crayon drawing or lithograph has been reproduced through the use of a line block exposed to a halftone. Style was no longer inherent to halftone techniques.

Postcard

As with any new process, time is needed to work out its problems, discover its nuances, and for its practitioners, gain experience in using it. Many early halftone images were printed too spotty or light and often suffered from poor clarity. As image quality improved, its place in the printing industry was guaranteed and its use quickly outpaced all other reproductive methods. Training in the printing arts passed from the traditional apprenticeship to technical trade schools once science began to steer the direction technology would take. Postcard production was torn between the many old printing firms that had perfected traditional techniques and the new entrepreneurs who saw in halftone an easy way to enter the postcard business. Both would continue to fight for market share throughout the years of postcard’s golden age. Growing economic pressures after World War One would eliminate most of halftone printing’s competitors.

Ives Process
There had been attempts to break up photographic images into small markings ever since Henry Fox Talbot introduced his photographic veils in the 1850’s, but the Ives process, invented by Frederick Ives in 1878 was the first in which a photographic image could be reduced to a series of black & white dots that gave the illusion of a full and accurate tonal range. This process begins when a photosensitive gelatin plate is exposed to a negative then washed out leaving behind an irregular surface of light hardened gelatin. A plaster cast is then made from the plate, which is then pressed against an inked rubber pad where the ink is only transferred to the highest points on the plaster’s surface. The contours of the cast capture the tonal shades as dots in proportion to the original tones of the photograph. The image pulled from the inked plaster cast is re-photographed, and then this new negative could be transferred to another photosensitive printing plate. This complicated process was patented in 1881 but abandoned by 1885 when Ives invented the much easier to use line screen. W.A. Leggo and G.E. Desbarats in Canada also developed a similar halftone process. The Canadian Illustrated News was the first newspaper to print a halftone image in 1869 using their method. In the years that followed, halftones created with the newer crossline screens were often incorrectly referred to as having been made by the Ives Process, but this was only due to the continued use of the recognized trade name.

Typogravure (Relief Halftone)
Typogravure was a method of halftone reproduction developed in France around 1890 that was very similar to the Ives process. The printing plate was cast from a photosensitive gelatin relief, formed when exposed to a halftone negative and then washed out. It contained many raised peaks of varying sizes from where the gelatin washed away in relationship to the amount of light exposure it received. These peaks were then rolled with ink and the plate was printed as letterpress. These delicate plates were soon abandoned when halftone screen techniques became available.

Meisenbach Process
The Meisenbach process, patented in Germany in 1882 by George Meisenbach of Munich and Karel Klietsch of Vienna was based on the early work of Ives. They created a line screen by etching parallel lines or small marks into a sheet of glass and then contact printing a positive transparency through it onto a negative. The line screen would be turned one or more times to break up the regular pattern and its exposure onto the same negative would then continue. The resulting negative could then be transferred onto a photosensitive intaglio plate or turned into a positive for use in lithography. Louis Levy of Philadelphia also developed a similar version of this type of line screen in 1887, and he became a major manufacturer of screens.

Crossline Screen
In 1887 Frederick Ives finally perfected the elusive halftone process with his invention of the crossline screen. This screen from which a halftone is produced is made from two sheets of glass into which a fine series of evenly spaced parallel lines have been etched and then filled with an opaque material. The first sheet of glass is then rotated ninety degrees to the second sheet and both are sealed face to face with a transparent cement to form a crossline grid. The spaces between the intersecting lines on this combined grid creates a field of tiny square apertures that will break up the tones of the image projected through it. Halftone negatives were made by photographing an image through a crossline grid placed at a calculated distance from its surface. Apertures that receive a lot of light cast a large dot, while apertures exposed to small amounts of light will cast a small dot. As the number of lines increase on a screen by placing them closer together, the halftone dots become smaller and more numerous creating a tighter frequency measured in dots per inch (dpi). A dense pattern of small dots will increase sharpness and render greater detail, but at the expense of decreasing the optical tonal range a plate can print. This new halftone negative would then be contact printed onto a photosensitized substrate. The halftone dots that results from this process only create the illusion of the full tonal range carried by the original photograph, in actuality its components are completely rendered in either black or white. Unfortunately for Ives, he never patented his invention mistakenly believing it could be better kept as a house secret.

Contact Screens
The contact halftone screen, invented in 1953 is used in direct contact with a photosensitized printing plate. It has made the creation of halftones much simpler than using a crossline screen because the exacting process of placing the correct distance between film and the image to be copied no longer needs to be carefully calculated. Contact screens have none of the usual opaque lines; these thin sheets of film are made up instead of small soft edged translucent dots whose density can be varied. This allows for a wider range of light modulation creating greater choices in producing tone. In general they pick up more detail and capture more subtle highlights and middle-tones than their crossline counterparts. Screens with grey dots are designed for creating color separations while magenta screens are used to create black & white halftones.



DOTS

Any marking of any shape or size produced by a screen during the halftone process is referred to as a dot. A variety of different dots including circles, ovals, squares, diamonds, and lines could be created by making even small adjustments to the way lines were cut into the crossline screen or by adjusting the angles at which the two halves were cemented together. These differing shapes were not created for any immediate aesthetic purposes since they are too small to be discerned by the eye. Each particular type of dot had their own practical advantages and disadvantages when printed.

Postcard Detail

Black & White Halftone: This detail displays the full range of halftone dot sizes that can be created with a single crossline screen. While all the dots are very similar they are still capable of creating hard edges, soft transitions, and a highly recognizable image despite their limited numbers.


There are many factors that will all affect the character of dots produced with a crossline screen such as the type of film used, the distance between the film and the screen, the size and shape of the lens aperture, and the intensity of light and length of exposure. Even with all these variables in play, the basic principal behind making a halftone remains the same. When light passes through an aperture of a screen, it will be brightest on the plate at its center fading off gradually around its margins. When dots grow in size they reach a density directly between highlight and shadow where they just begin to touch each other (optical bump) and a checkered pattern is formed. On the shadow side of the bump the dots appear white, and on the highlighted side they reverse and appear black.

Postcard Detail

Line Block Dots: Above is an enlargement of a black & white line block showing the dots created through halftone screening. The detail below comes from a hybrid color line block.

Postcard Detail


Postcard Detail

Lithographic Dots: Above is an enlargement of a hybrid color lithograph showing the dots created through halftone screening. The detail below comes from an offset lithograph.

Postcard Detail

Even though line screened transparencies or negatives can be directly transferred to a printing substrate, they usually undergo heavy retouching by hand. When all the stray dots in areas needed to print white were removed and the edges of the darkest tones were made solid to eliminate tonal transition, the results are known as a highlight halftone. The size of dots on halftone positives could also be reduced with chemicals, and this is known as dot etching. When dots on the metal plates used in gravure or line block were retouched, this is referred to as a fine etch.

Postcard

Halftones: While the principals of halftone printing remained constant, the results often differed when applied to a different medium. Soft dots are produced when they are placed on a stone as depicted on the lithographic postcard above. When used in conjunction with line block printing as seen below, the halftone pattern from the metal plate retains its sharpness and clarity.

Postcard


Postcard Detail

Halftone Details: In these two details taken from the postcards further above we can better see how the quality of dots can differ between mediums. The dots printed of a litho=stone pictured above appear soft, while the dots printed by a metal line block plate below have sharp edges.

Postcard Detail


Postcard

Line Blocks: Both of these hand colored line block postcards look very similar but the image above consists of random marks from a textured drawing and the one below was made entirely with halftone. When halftones are used to their best advantage, as when imitating another technique, they disappear to the naked eye.

Postcard

Even when the same crossline screen was used to create a halftone, the characteristics of the resulting dots could differ depending on the printing medium employed. The dots on line blocks tend to display sharp clear edges because there is nowhere for the excess ink to go once pressure forces it to the edge of the relief. The minute amounts of ink that gather at the edge to form line squash only print darker reinforcing the dot’s sharpness. Lithographic dots from a stone or plate are more uneven in size and they have fuzzy edges because of the texture inherent in the substrate. Dots printed in offset lithography will have an even softer look because the ink spreads out when transferred onto the rubber roller of the press before being printed. When any halftone is printed on poor quality or uncoated paper, the individual dots have a tendency to bleed outward and even sometimes together (dot gain) resulting in a loss of detail. When printing off of a rotary press the surface of the plate and that of the paper on the cylinder has to make perfect contact to yield a good impression. Any flaw in the plate or lack of adequate printing pressure can create a mottled image.

Illustration

Euclidean Dot: This pattern reads as black round dots on a white field in light areas but it morphs into a square checkered pattern at the mid-tone optical bump. As it continues to get darker, it mirrors the first pattern reading as white round dots against a black field. This pattern is the standard result of photographing an image though a crossline screen, and it was the most widely used in the creation of postcards.



Illustration

Elliptical Dot (Rhomboid): Elliptical dots can be printed in the same manner as other dots, but as those on the same axis grow bigger they begin to merge at their ends forming a chain like linear pattern (chain dots and chaining lines). This trait of oblong patterns is used to better render mid-tone values and create smoother tonal transitions. Many postcards can be found with chain dots, and their use has become widespread.



Illustration

Round Dot: The round dot pattern gives better control of light tones but it renders a softer image, which in turn means the loss of detail. It is truly non-directional for it appeared the same when printed at any angle making it popular for use on high speed presses.



Illustration

Square Dot: Square dot patterns have the ability to render edges that are sharper than those produced by other patterns, thus yielding greater detail than its counterparts. Unfortunately the tight pattern creates a tendency for white dots within the darker areas to fill in during printing.


Mezzograph Dot
The mezzograph screen consisted of a single pane of glass on which the individual random markings acted as a lens. The results were a dense irregular texture similar to that of a mezzotint though the markings are much too big to actually be mistaken for one. The unusual screen pattern is created by the reticulation of gelatin as used in the ink-photo process, which is why these images have a resemblance to a collotype; only here the pattern is about ten times larger. Since this screen did not create a linear pattern it was primarily used to reproduce other types of line work such as engravings to eliminate the possibility of undesirable interference patterns forming by the crossing of two sets of parallel lines. Digital technology also makes reference to mezzotint dot patterns but their only connection is in their randomness, not the actual look of the markings.

Postcard

Mezzograph Halftone: The texture on this postcard printed in line block was created with a mezzograph screen. It gives the image the drawn look of a crayon rather than a mezzotint. While it is almost indistinguishable from an ink-photo printed in lithography, the technique was rarely used to create postcards in the twentieth century.

Postcard Detail


Postcard

Mezzograph Halftone: The mezzotint like texture on this postcard printed in line block is meant to give it the drawn look of a crayon. This particular pattern is so large and open that it can be debated whether it was shot through a mezzograph screen or drawn in by hand with the aid of a paper tint embossed with a mezzotint pattern.

Postcard Detail

One Way Line
A one-way screen was designed to break down a photograph into a series of lines instead of dots. Its overall effect yielded an image that was supposed to be reminiscent of a fine engraving but was more similar to the results achieved from paper tints designed to have the same visual effect.

Duel Dot
When two different color halftones needed to overlap, different types of screen dots were often employed to avoid creating moiré interference patterns. While this helped, each screen still needed to be rotated to a different angle from one another before being transferred to a printing plate.

Postcard

Double Halftone: This image is printed with only two line block plates. One carries the details of the image in a black Euclidean halftone key, and the other plate has a red elliptical halftone added in for color. Moiré patterns were avoided by exposing each halftone through screens rotated to different angels. The detail of the sky pictured below shows how the oblong red dots have joined to form chain lines.

Postcard Detail

Frequency
Halftone screens were created with lines placed in standard rulings ranging from 50 to 300 lines per inch. They in turn would produce the same amount of dots per inch (dpi). The more lines placed into a screen the smaller the dot produced. There was a cost benefit ratio as to how many dpi to use; small dots could render much more detail than large ones but as they grew smaller the overall tonal range within the image would decrease proportionally. Large dots could create images with bold contrast but could not capture fine detail. The entire possible range between optimized detail and contrasting value was used in the printing of postcards.

Individual halftone dots are usually printed so close together that they are not observable to the naked eye. On some cards their patterns are so tight that they resemble continuous tone lithography. There were however publishers like newspapers that produced postcards where the screen pattern is clearly visible. Large dots in an open halftone were required when printing on rough paper like newsprint to prevent the image from filling in. While these restrictions did not normally apply to the printing of postcards, the use of known procedures at existing facilities greatly reduced cost, and so the same type of halftone was used to create both products. Unfortunately once the dot pattern became observable to the naked eye, it defeated the main purpose of the halftone process, which was to create the illusion of continuous tone. The quality of these types of postcards tends to be very low.

Postcard

Collotype and Halftone: The postcard above was printed as a collotype, but when the publisher had it reprinted, he chose another firm that produced the card below in halftone. While the halftone does a fairly good job in rendering tonal gradations, the loss of nuance from that of the collotype is still discernible to the naked eye. While the two cards look different from one another, the reasoning behind this change was probably to cut cost, not to alter appearance.

Postcard


Postcard Detail

Collotype and Halftone: In these details of the two postcards pictured further above, it is easy to see the unmistakable differences in tonal gradations created in the collotype above from that of the halftone below. Under normal viewing conditions dissimilarities fade as the halftone does an adequate job in fooling the eye into believing it is seeing tone. This is attributable more to how the human brain interprets stimulus than any optical properties of printing.

Postcard Detail


Postcard

Line Block Halftone: Most of the time a black & white image printed in halftone is discernible even when the dots cannot be seen because of an overall coarseness about them. This however is not always the case for the halftone card above comes across as a continual toned picture. The frequency of dots chosen to reproduce this image matched perfectly to produce rich dark tones normally associated with gravure or heliotype.

Postcard

Line Block Halftone: On this postcard published by the Brooklyn Eagle, the large halftone dots are so apparent that the production method is unmistakable. The enlargement below reveals so few details within the open pattern that it almost becomes a pure abstraction.

Postcard Detail



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