Read Ebook: The Mentor: Photography Vol. 6 Num. 12 Serial No. 160 August 1 1918 by Anderson Paul

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There are about fifty different reducing agents on the market; most of them are derived from coal-tar, though some are made from nut-galls, lichens, and other substances. The developer consists of a solution in water of one or more of these reducing agents, with other chemicals to control the action, the exposed plate being bathed in this solution, either in the dark or in a light to which the plate is not sensitive. Wherever light has acted on the silver salts the developer causes metallic silver to be deposited in proportion to the amount of light-action, so that on holding the developed plate up to the light a dense deposit is seen in those parts representing the brightest portions of the subject, while the shadows of the original are represented by thin areas, and the half-tones by deposits of intermediate density. For this reason the developed plate is called a negative. The plate is then bathed in a solution of sodium thiosulphate , which dissolves the unaffected silver salt but does not affect the metallic silver--or at least does so only very slowly. Next, the plate is washed in water to remove all unnecessary chemicals, and is dried. The ordinary plate is sensitive only to ultra-violet and violet light, so it cannot render truthfully any subject having color, but by the addition of certain aniline dyes to the emulsion it may be rendered sensitive to green in addition to violet and ultra-violet; it is then described as orthochromatic or isochromatic . Still other dyes extend the sensitiveness to include not only ultra-violet but also the entire visible spectrum; such a plate is called pan-chromatic .

The finished negative, when dry, must of course be printed, and there are many printing mediums available. The carbon process gives an image in lamp-black or some earth pigment, bound up in a film of gelatine; the gum-pigment process gives an image similar to that of carbon, the binder in this case being gum arabic; the platinum process gives an image of black metallic platinum direct on the paper support. Other processes give different effects, one of the most valuable to the pictorial worker being gum-platinum, in which a completed platinum print is coated with a gum-pigment film and printed under the negative a second time, the final result being a gum-pigment image superposed on the platinum image. Of all printing mediums the one that has most intrinsic beauty, and is at the same time most capable of rendering satisfactorily the gradations of the negative, is probably platinum, so this is most used by pictorial workers. But, since it is expensive and requires daylight or strong artificial light for printing, nearly all commercial workers prefer the somewhat less beautiful and less permanent, but more convenient, gas-light paper, so-called because it can be manipulated entirely by gas-light, neither daylight nor a dark-room being required. This medium consists of paper that has been coated with an emulsion somewhat similar to that used for plates, but requiring much longer exposure. The negative is placed in an appliance that holds it in close contact with the paper, then a sheet of paper is put in, and an exposure of a few seconds is given. Obviously, the paper receives most light under the thin parts of the negative and less under the denser portions, so that when the print is developed, fixed, washed and dried the resulting picture is light where the original subject was light, dark where that was dark, and show intermediate gradations where these existed in the original.

For purposes of reproduction two processes depending on photography have almost entirely superseded the older methods of etching and wood engraving. These photo-mechanical processes, as they are called, are far more rapid and much cheaper, and are, in addition, more accurate. In photo-gravure the photographic image--copied by photographing the original--is transferred to a copper plate and the plate is automatically etched in an acid bath to varying depths, depending on the depth of shadow in the original. This plate is then inked all over, the ink being worked into the depressions in the copper, and the surface ink wiped off. A sheet of paper is brought into contact with the plate under heavy pressure, and, being forced into the hollows of the copper and taking up the ink from them, a print results. In the less beautiful but cheaper and more rapid half-tone process the copy is made through a cross-ruled glass screen, the image being thus broken up into a series of dots. The image so obtained is transferred to a zinc plate, which is etched in an acid bath or with an acid spray. The dots serve to protect the zinc from the action of the acid. The finished plate shows an image consisting of dots with hollows between them, the dots being large and near together in the shadows, small and far apart in the lights. This plate is inked with a roller, and a sheet of paper, lightly pressed against it, takes up the ink to form a print. Thus it will be seen that photo-gravure is an intaglio process, and half-tone a surface-printing process.

See cut on page 9.

Despite the limitations of the camera as regards imaginative work there is a small but devoted band of photographers who use the camera as a means of artistic expression, and these men and women have produced some wonderfully fine results that fulfil the definition of art: "A means of arousing an emotion in the spectator." In the last analysis, however, it will be found that such results are due to one of two methods of approach: either the careful selection of an unusual natural effect, or the use of one of the so-called "control processes"--that is, printing mediums that allow the worker to modify at will either the outlines or the gradations of the negative, or both. In the former case, however, the photographer cannot be regarded as more than an exceptionally sensitive and perceptive craftsman, and in the latter instance the camera user, of course, ceases to be a photographer and becomes a creative artist, using photography merely as a basis on which to construct an imaginative result. The possibilities of this second method of work have not yet been fully explored; they appear to be limitless.

The literalness of photography, which prevents its ever competing with etching or painting in imaginative art, makes it of inestimable value in certain realms, and scientists of all sorts, astronomers, physicists, physicians, pathologists, as well as architects, building contractors, business men, who wish a precise and accurate record of any object, recognize the value of the camera. Photographs are often admitted as legal evidence in court. It is impossible to overstate the value of the dry-plate to the surgeon, since the X-ray, generated by passing an electric discharge through a glass tube from which most of the air has been exhausted, penetrates many objects that are opaque to ordinary light, and, though invisible to the eye, nevertheless affect a photographic plate, thus making possible a precise diagnosis of fractured bones, gun-shot wounds, digestive disturbances, and many other pathological conditions in which diagnosis without a radiograph would be mere guesswork.

In portraiture, photography is superior to any other graphic art, since the camera worker can, by judicious selection of lighting, pose and facial expression, render the character of the sitter quite as well as the draughtsman, this being the final test in portrait work, though it must be admitted that few portrait photographers meet this requirement.

The human eye and mind are, from a mechanical point of view, but imperfect instruments. Admirably as they serve the purpose for which they are designed, it is nevertheless impossible for them to observe with absolute accuracy. The camera, however, has no such limitations; its observations are accurate and its records unquestionable, so long as no definite effort is made to impair their exactness. For this reason photography is used not only in astronomy but in many other branches of science, among its most important uses being the making of records of microscopic objects.

A device carrying a photographic plate is attached to the eye-piece of a microscope; the plate being exposed affords, on development, a precise record of the subject under observation. It may be noted that in this case, as in astronomical photography, no camera lens is required; the microscope, like the telescope, projects an a?rial image which is impressed on the plate. It thus becomes possible for the microscopist to study at leisure a photograph of the object that was in the field of the microscope, and thereby eliminate eye-strain and minimize the likelihood of overlooking any feature of interest. It is further possible to make lantern-slides from the negative so obtained. A lecturer by this means is enabled to show the photograph to a large group of individuals simultaneously.

In the case of some objects, a fuller knowledge of their character is gained if they are examined in a manner somewhat different from that usually adopted. One of the photographs given herewith shows the effect obtained by what is known as "dark ground illumination." Ordinarily, the light by which a microscopic object is examined passes through the slide, so that an opaque object is really seen only as a silhouette, but in dark ground illumination an opaque background is placed behind the object, and the light is allowed to fall on it from the sides. The object is thus made visible by the light that is refracted into the lens of the microscope. In the present instance the effect seen by looking into the eye-piece was wonderfully beautiful, the crystals glowing with a brilliant yellow light against an intensely black ground.

Some persons object to the inclusion of radiography as a branch of photography, since no camera or lens is used, but "photography" means, literally, "light-writing," and radiography is precisely this.

If the air be nearly exhausted from a glass tube, so that a high vacuum exists therein, and it be then sealed up, a current of electricity may be sent through the remaining air, setting up ether vibrations that pass out from the tube. These ether waves have the power of passing through many substances that are opaque to visible light, the X-rays, as they are termed, being totally invisible, though light waves to which the eye is sensitive are set up at the same time within the tube. Many persons confuse the greenish light from an X-ray tube with the X-rays, but the two are actually entirely different manifestations. The X-rays, though invisible to the eye, are nevertheless able to affect a photographic plate strongly, so that photographs may be made through solid objects. For example, if a sensitive plate be laid on a table and the arm or the hand placed on it, and an X-ray tube is brought near the arm, a photograph results in which the bone is represented as a dark area and the flesh around it as lighter, this being, of course, simply a shadow picture. This affords an intensely valuable aid to diagnosis, and a good surgeon will, if possible, first radiograph a fractured bone before setting it, unless the circumstances are very exceptional. The value of radiography is not, however, confined to fractures, but extends to wounds , to many intestinal disorders, and to the diagnosis of other diseased conditions.

Though not strictly bearing on photography, it is interesting to note that the X-rays, like the "gamma rays" of radium, are in reality ether vibrations of very short wave length, and like the shorter waves in sunlight, possess curative powers in some skin disorders and also the power of causing terrible burns. Sunburn does not result from exposure either to visible sunlight or to the heat of the sun, but to the ultra-violet rays; and an X-ray burn is identical with sunburn. In extreme cases the X-rays may cause complete destruction of the skin and even cancer, and before the properties of the X-rays were so well known as at present many operators lost hands, and some their lives, as a result of excessive exposure to the rays. At present, X-ray workers shield themselves, and, when necessary, the patient, with lead screens, that metal being practically opaque to the rays.

Many workers have tried, with varying success to devise a means whereby photography could be made to reproduce not only the outlines and gradations of natural objects but the colors as well, and there is now available a method of great worth for this purpose. In brief, it consists in making, by one exposure in an ordinary camera, a set of three-color negatives, each of which represents that portion of one of the primary colors--violet, green and red--which was reflected from the subject. That is, one negative represents the violet "sensation," the second the green, and the third the red. Prints are made from these negatives in suitable dyes on transparent films, which are cemented together, one over the other, thus giving a true color photograph, in which the secondary and tertiary colors--blue, yellow, orange, purple, brown, etc.--are obtained, as in painting, by the mixture in proper proportions of two or more of the primaries. This is the first method of color photography to possess the great advantage of producing prints--not transparencies, so that any number of duplicates may be made. No special camera is required, and the process is within the reach of any careful amateur. The writer believes the artistic value of color photography is relatively slight--a black and white art is capable of the fullest intellectual expression, and color is merely sensuous in its appeal. After much experiment with different color processes, he finds his own monochrome prints more satisfying than the color work. However, the value of color to the scientific worker is incalculable, as will be realized at once on considering only one of the possible applications--namely, the study of skin affections. It is interesting to note that several methods have been devised for the reproduction of natural colors in motion-picture work--the familiar method of coloring the positive film by hand being only an approximation to truth. But none of those presented up to this time is fully satisfactory, though the prospects of future development are good.

When we consider the manifold and widespread uses of photography and the pleasurable diversion that it affords, it seems safe to say that there is no other form of industry not an actual necessity that is of such importance to the welfare and happiness of the human race.

? Information concerning the above books may be had on application to the Editor of The Mentor.

One summer afternoon, some years ago, I went into a front room of my home and drew down the window shades to shut out the glare and heat. The room became quite dark, but, in one of the shades, there was a small hole, through which the sunlight penetrated--casting on the white wall opposite, vivid images of all the objects in the street outside. I had before me a full-color, moving picture of the panorama of life that was passing the window.

Here was the original "camera obscura" . If one placed in the small hole in the shade a glass lens to give a sharp image, and substituted for the wall a movable screen, on which the projected objects could be focussed, one would have the essential elements of a modern camera. Through just such simple experiences as this important scientific discoveries are sometimes made.

Consider briefly a few of the wonders of modern photography. First and foremost, and most spectacular of all, is the moving-picture film. Then, in the world of practical things, we have the telephoto-lens--a combination of the telescope and camera--that takes pictures of objects far beyond the reach of the naked eye. This enables one to photograph the head of a gargoyle on a distant cathedral, or the fledglings in an eagle's nest, or a mountain goat on a crag high up a mountain side. Then there is the swinging camera, by means of which a wide sweep of view can be included in one plate. A device of great practical value is photo-telegraphy, by which portraits for purposes of identification can be sent by cable and by wireless. In modern warfare the uses of the camera are many and varied. They include panoramic photography, photographing by moonlight, photographing of projectiles in the air, even photographing the noise of a gun by recording the vibrations due to the displacement of the air, photo map-making, photo surveying from the air, and the aviation gun camera. Radiography, too, must be mentioned--the X-ray and its use in surgery.

While all these wonders have come to pass in practical service, photography has likewise grown and expanded in the field of fine art. There are photographic art schools, and clubs and exhibitions--all for the purpose of cultivating and developing the camera to the finest forms of expression. We have highly cultivated and skilled photographers who are true artists, and who are engaged in employing photography as a means to fine art achievement. Among such artist photographers in this country mention should be made of Mr. Paul L. Anderson--the author of the present article; Arnold Genthe, who, besides his wonderful portraits, has, by his art, preserved for future generations the scenes of old San Francisco--especially Chinatown--that have now passed away; Gertrude K?ebier, Baron de Meyer and Jan de Strelecki, Stieglitz, Eyckmeyer, Steichen, S?mons and so many others that the list would fill this page.

What, Who, and When?

WHAT IS PHOTOGRAPHY?

It is the science and art of producing pictures by the action of light on chemically prepared plates or films.

WHO DISCOVERED PHOTOGRAPHY?

No one particular individual. There is no known date on which "photographic action" was first recorded. The action of the sun in making impressions of one sort or another on surfaces was known to man from the earliest times. Records of it can be seen in fossilized vegetable remains--and this action of the sun is apparent in the change of color that takes place in the ripening of fruits and foliage.

WHO FIRST APPLIED A SENSITIZED PLATE TO THE PURPOSE OF MAKING PHOTOGRAPHIC PRINTS?

No single individual discovered this essential principle of photography. It came to be recognized in the course of many experiences, beginning with the alchemists; and developing through the experiments of a number of investigators, until the end of the eighteenth century, when the sensitiveness of various silver compounds to light became well known, and the character of the change produced on these compounds by light became established. Thomas Wedgwood, the fourth son of Josiah Wedgwood, the renowned potter, developed a process by means of which the image printed by photographic means could be "fixed" and made permanent.

WHAT INSTRUMENT BROUGHT THE PHOTOGRAPHIC PROCESS TO A PERFECTED FORM?

The camera. The camera is the photographic apparatus in which the image is projected upon the sensitized plate, thus securing a photographic impression. The word "camera" is Italian for "room," and the full name of the original instrument, "camera obscura," means "dark room."

WHO INVENTED THE CAMERA?

Giovanni Baptista della Porta, who lived in the sixteenth century, has often been stated to have invented the camera, but he appears only to have popularized and improved it. The first use of cameras was not for printing photographs, but simply as an interesting toy or to assist one in tracing the outlines of various objects. There are many applications of the "camera obscura"--a notable one being the periscope of a submarine. It was not until a suitable sensitive plate was discovered that the camera became useful as an apparatus of photography.

WHO WERE MOST PROMINENTLY IDENTIFIED WITH THE DEVELOPMENT OF THE PHOTOGRAPHIC PROCESS?

Joseph Ni?pce and Louis J. M. Daguerre. Ni?pce was successful not only in getting pictures produced in the camera, but he succeeded in "fixing" them permanently, Daguerre developed a process known as "daguerreotype," which was the first method of photography available for practical purposes. This was in 1837. With the general acceptance of daguerreotypes, photography became a profession. The process had no rival until about 1851, when the "collodion process" was discovered, and, after that, the daguerreotype process became obsolete.

WHO DEVELOPED THE MODERN PROCESS OF PHOTOGRAPHY?

William Henry Fox Talbot, an English inventor . He greatly increased the sensitiveness of paper, and from his negatives prints were produced in much the same way as in the present day.

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