THE halftone is a form of engraving in very wide use, though the most recent of all the great forms of pictorial reproduction. Its development dates only from the late eighties of the last century, and its general commercial use may be said to have begun about the year 1890.
It is the most photographic of all the general forms of illustration, and it has been aptly described as “a mechanical method of reproducing in a printing plate the details of a photograph, drawing, painting, or an object itself, including all gradations of color.” Its name obviously is derived from its ability to reproduce the grays and half tones, whereas the line etching is confined to solid colors.
Great developments in the entire printing and advertising industry followed the perfection of the halftone process. For a time it largely superseded other forms of engraving in the finer work. By its nature it called for a smooth printing paper, and the rise of coated or enameled paper stocks followed immediately in its wake. As the color process developed, a great deal of work that had formerly been done by stone lithography was executed with halftone plates.
While its position in the graphic arts is secure and it will always have a very wide application, it may be said with authority that in recent years there has been a certain reaction toward the earlier type of engraving. This is attributed by many writers to the revival of professional and public interest in fine typography, often based on the earlier classical models. With this has come naturally an increased use of antique text papers, whose surfaces possess great “character,” but are not adapted to the fine screen of the halftone plate.
The process of the manufacture of the halftone is, generally speaking, so similar to that of the line etching that it need not be reviewed in detail. The main difference lies in the principle of photographing the copy for the halftone through a glass screen, etched with cross lines at right angles, so as to cut the picture into minute squares, forming dots in the printing plate. The effect is quite the same as that of the wires in an ordinary window screen. The designation of the various types of halftone plates is based on the number of parallel lines to the inch in the screen. Sixty to the inch is perhaps the coarsest screen in general use, while 15o to 175 to the inch are the finest with which the advertiser is likely to have any serious concern. These are not the limits of manufacture. Plates are made as low as 5o to the inch and as high as 400. The 133-line plate is probably the most widely used for general purposes. The commoner commercial screens are 6o, 85, Too, 120, 133 and 150.
The screen ordinarily in use in engraving establishments consists of two pieces of fine plate glass attached with a transparent cement, the engraved or etched sides together. Parallel lines are engraved on each of the plates, and these lines are rendered opaque by rubbing a pigment into them. When the two plates of engraved glass are put together the etched lines are, of course, placed at right angles. While most screens are rectangular in shape, the cross lines are not made vertical and horizontal, but are engraved at an angle of forty-five degrees to the edges. The screen in the printing plate at this angle greatly reduces in conspicuousness the screen pattern effect that is inherent in all halftones, though much more marked in those of coarse screen.
The cross etching divides the surface of the glass screen into a multitude of small squares, and in making the negative for a half-tone this screen, duly selected for fineness, is placed before the sensitized plate in the camera while the exposure is being made. Each little square in the screen acts as a diaphragm through which the light passes on to the negative of the copy, forming through it a microscopic part of the final picture.
The properties of the light are such that, though the little squares on the screen are all of one size, by altering the distance between the screen and the photographic plate the stronger rays of light that come from the lighter parts of the subject or copy spread and make larger spots in the negative. Those from the darker parts of the copy make very minute dots on the negative. When the negative is transferred to the copper plate these conditions are reversed and the high lights are represented by the smaller dots and the dark parts by larger dots, which may practically converge into a solid color. By this variation of the size of the dots every gradation of tone in the copy is reproduced with comparative fidelity.
It will be apparent, however, that by the very nature of the process, it reproduces all images in dots. A pure white or a dead black cannot be got photo-mechanically without special treatment, as the white will contain microscopic black dots and will be in fact a very light gray, while the black will have a certain number of openings or depressions in the plate through which the stock will show and will be in reality a very dark gray.
This is one of the limitations of the halftone inherent in the process, but it is approximately overcome by special manipulation in making the negatives and by hand work on the plate, known as staging, tooling, burnishing, etc. A section that should be white can be tooled out so that all the dots in that part are removed, and in the black part the dots can be run together by staging or darkened by burnishing. These special finishing processes naturally add to the cost of the plates.
In the use of the halftone a great deal depends on the character of the paper and ink. The best results are obtained by the use of a fine screen and a very smooth enameled paper. These general rules will apply:
The coarser the screen, the rougher the paper that may be used; but there is a great sacrifice of detail as the screen is enlarged, and the picture will show decided screen marks. A close observation of any newspaper halftone will reveal these defects, and they will become exceedingly apparent when the examination is made through a magnifying glass. If an effort be made to print fine-screen half-tones on a paper of rough finish, the plate shows a decided tendency to fill up and to print as a black smudge. Failures of this kind are often seen in cheap advertisements and in small newspapers, where any halftone that happens to be in stock will be used when occasion for that particular picture arises.
It is wise to use as fine a screen as the surface of the paper and the skill of the printer will permit; but if there be doubt, it is probably safer to err on the coarse side and to sacrifice something of final effect rather than risk a complete botch and failure. Consultation with your printer is desirable before deciding on the fineness of halftones for any particular job.
The inexperienced printer can work far more safely with coarse halftones than with fine ones. Much thinner inks can be used on coarse halftone plates than on fine screens. A very stiff ink, a very fine screen, and a very smooth paper constitute the best possible combination when especially fine results are desired. If you lack other guidance it will be well to send to your engraver a sample of the paper on which you propose to print the plate that is being ordered and to inform him exactly how it is to be used. His large experience will enable him to make a suitable engraving for the purpose in mind.
The depth of the chemical etching is another very important consideration to the buyers of engravings. The coarser the screen the deeper the etching possible, but there may be a variation in even the finest screens. If circumstances make it desirable to use a fairly fine screen on a rough paper, the engraver should be directed to etch the plate more open and deeper than is customary. Half-tones for use on cover paper should be deeply etched.
The question of making electrotypes from the original halftone is often vital. The finer the screen and the shallower the etching, the more difficult it becomes to make an electrotype from the en-graving without substantial loss of character. Indeed, it may be said to be commercially impracticable to make electros from the very finest halftones, though especially expert electrotypers may succeed. Before ordering electros from very fine plates, one should be assured by the electrotyper that he can guarantee the result.
As original plates are expensive, and there is a further economy in printing advertising several at a time, it is obviously uneconomical to use original plates in large runs unless the work is so important that quality of result overcomes all considerations of economy of manufacture.
The etching process must be skilfully conducted if serious difficulties are to be avoided. The sides of every dot on the plate should taper conically. If the etching be too deep and the acid is allowed to undercut the base of the dots, several sources of grief are courted. The points may actually break off; the plate may pick up the paper, each dot acting as a small hook, or it may tear the mat or mould in the process of stereotyping or electrotyping.
Halftone plates are usually made on copper if the best printing result is desired. But if speed and economy are more important than fine results, as in a newspaper office, zinc may be used for the coarser screens. The metal is cheaper and etches more rapidly. The terms “newstones” and “quartertones” are sometimes applied to plates of this type.
Halftone plates are finished in various forms. The more common type is rectangular, and is referred to in the trade as a “square finish.” It is made either with a black line around the border, or with “no line.” This is the cheapest form of halftone and, especially in the smaller sizes, is the easiest to print. Any halftone of large area requires most careful make-ready, as an uneven impression will ruin the effect.
The outline halftone is one in which the background is entirely cut away, printing the reproduction in the exact shape of the original. The figure or object thus treated stands out more conspicuously than if set into a background.
The vignette halftone is one in which the picture or back-ground has no sharp definition, but blends gradually into the paper. It is a very artistic treatment for the proper subjects, but should be attempted ordinarily only when the work is of a high character and certain to be well executed. The copy must be vignetted before the plate is made. There is an extra charge for vignetted halftones.
Combinations of the various forms are frequent. A part of the picture may be square, oval, or in outline and a part vignette. These combination plates are called by engravers “square-vignette,” “outline-vignette,” etc. Especial care must be used in giving clear and definite instructions to the engraver when such plates are ordered.
There are a number of special types of halftone, but these will have only a casual interest for most advertisers. The mezzograph is a plate made from a grained screen instead of from the usual cross-line screen. Its principal use is for a tint plate to work with old plates, or for reproducing prints from other halftones or engravings. If a halftone be made by the usual process from a print from another halftone, the superimposing of the two patterns of dots is very likely to give a wavy or moire effect. The mezzograph screen reduces this danger.
The one-way-screen halftone is a special halftone in which the printing surface consists of lines instead of dots. It is obtained by the use of a special stop in the camera when making the negative, and gives effects comparable to wood engravings. Such other forms as the duotype are referred to later under the subject of “Color Printing.”
Photographs, plain or retouched, and wash drawings are the most common forms of copy for halftone reproduction; but pen and pencil drawings, paintings in oil or water, pastels, crayons, and even the products of other forms of engraving may be reproduced with varying degrees of success. The finest copy no doubt is a sharp, clear photograph printed on glossy paper. As the half-tone is a photographic process, reproducing just what is in the copy, it is very important to see that good copy is provided when possible. A skilled artist can often improve poor copy by retouching, but this adds to the expense. Copy should be larger than the final plate, as small imperfections and crudities tend to disappear in reduction, whereas they are magnified in enlargement. This rule applies especially to wash drawings and to photographs on which considerable retouching has been done. An examination of a retouched photograph as it comes from the artist will make the wisdom of this rule apparent at a glance.
When halftones are to be made from paintings or colored copy, special photography involving the use of the panchromatic plate and color screens is usually necessary.
As to the adaptability of the various screens of halftone to different uses and kinds of paper, Mr. Hackleman, in his Commercial Engraving and Printing, shows a series of plates, with this comment:
“Sixty-line ScreenFor newsprint and low-grade papers. Stereotypes and electrotypes well. Used by most large news-papers and by some mail-order and agricultural magazines.
“Eighty-five-line Screen For news and lower grades of machine-finish papers. Electrotypes well and stereotypes fairly. Used by some metropolitan newspapers and many small newspapers, by many agricultural papers, and by a few magazines and business papers.
“One-hundred-line ScreenFor super-calendered papers and, when deep-etched, for the smoother cover papers. Electrotypes well. Used by many magazines and business papers and by some agricultural papers.
“One-hundred-and-twenty-five-line ScreenFor super-calendered book papers. Electrotypes well. Used by many magazines and business papers and some farm papers.
“One-hundred-and-thirty-three-line ScreenFor super-calendered papers, dull-finish coated papers, and the lower grades of gloss-enameled papers. Electrotypes well. Used by many magazines and business papers.
“One-hundred-and-fifty-line Screen For enamel book papers. If electrotyped should be by the lead-mould process. Used for catalogues and other high-class advertising on coated paper.
“One-hundred-and-sixty-line Screen For enamels only. Used for finest catalogues and other high-class work for which enamel papers are suitable. Electrotypes should be by lead-mould process.
“Three-hundred- and Four-hundred-line ScreenAdapted only to the very highest grades of enamel paper. Suitable for use only where microscopic detail is necessary. Can be electrotyped only with difficulty and by the most skilled craftsmen. Requires the most careful make-ready, very slow printing, and frequent wash-ups.”
Before leaving the subject of halftones it may be well to refer to combination plates, because the halftone is almost always part of that combination. Strictly, the combination plate is one made up partly of a line etching and partly of a halftone, though the term has been extended to include a variety of special effects.
One of the great advantages of the combination plate is that it makes it possible to secure high attention value, and better printing qualities can be obtained under most conditions than by the use of the halftone alone. Any kind of background may be worked around a photographic image, and any feature of the picture may be emphasized as greatly as desired.
Special effects are procured in a variety of ways. Plates that have been made by different processes may be fitted and mounted together, or the negatives may be stripped together to make the print on one metal plate. Effects may be varied by many processes familiar to all good engravers. Borders, lettering and deco-rations made in line engravings will print with better results, as a rule, than if made by the halftone process.
The high-light halftone is a plate in which the elimination of the dots in the high lights is accomplished by a chemical process instead of by hand tooling. They are more costly than standard types, and are used a good deal in magazines, books and large edition work for which their cost is warranted. The plates are quite open and are easier to print than the usual halftones. Copy must be specially prepared. The high lights are retouched or painted into pure white, and the middle and dark tones tend to end abruptly instead of blending. In combining drawn back-grounds with photographs where high lights are desired, the back-grounds are usually sketched in with pencil or pen and the photograph mounted with the drawing.