PhotoHistory

From: PHOTOGRAPHY OF TO-DAY

By H. CHAPMAN JONES, 1913

In following the development of photography from its beginnings it is clear that the compounds of silver have always occupied a very important position. But innumerable substances are changed by the action of light, and if silver and its compounds had never existed photography would still be not only possible but practicable. No two substances that we can distinguish from each other are alike, for if they were they would be only different portions of the same substance, nor are the changes that they undergo exactly the same. When therefore we have a large number to select from, the problem is to choose those that offer the most substantial advantages.

The changes that light produces in silver compounds certainly were and probably still continue to be the most obvious of all such changes. Under suitable conditions silver chloride darkens almost to blackness by an exposure to daylight that is not very prolonged. This fact created a prejudice in favor of silver compounds, and it was this that led to the discovery by Fox Talbot that a short exposure to light, so short as to give no visible result, produced an instability in the parts exposed that enabled a suitable substance to produce the blackness, by its application after the light had been withdrawn. And it is in this that the particular value of silver compounds consists.

What concerns us especially now is that by this course of events the brighter the object is, the denser is the deposit produced by its action on the sensitive surface in the camera, and if this deposit is dark, the bright parts of the object are represented by dark deposits in the image. The bright sky is represented by blackness on the plate, and the dark foliage leads to the production of very little deposit, so that we get a total reversal of light and shade. That brightness should produce darkness seemed to tickle the fancy of Schulze, who started out, as Daguerre appears to have done, by the endeavor to make or use a preparation that would shine more brightly in proportion to the brightness of the light that fell upon it, as we now say would phosphoresce. This that seemed to be a grave disadvantage to some of the earlier workers, has proved to be of the greatest service, because if this reversal of light and shade can be obtained once it can be obtained a second time. If the first photograph is used as a shield to a piece of sensitive material placed close against it while the two are exposed to light, the black sky protects the sensitive surface beneath it and then there is little or no action, while the thin deposit in the shadows allows the light to pass more freely and produce the darkness that corresponds with the original object. Sir John Herschel called the first photograph a “reverse transfer” or “first transfer,” and the second “a second transfer or re-reversed picture.” Shortly afterwards, “to avoid circumlocution,” he called the first a “negative” and the second a “positive,” and although these words do not etymologically convey the meaning attached to them, they have served their purpose in photographic nomenclature for seventy years, and doubtless will continue to do so. The great advantage of this method of work is that a negative will give any number of positives or “prints” without any further recourse to the original object.

But this method of work has another advantage, in addition to the facility that it offers for multiplying the photographs, that is not often appreciated. Any photograph that is obtained directly in the camera as a Daguerreotype is, is “reversed” in quite a different sense from the reversal just referred to. It is optically or laterally reversed. You have only to look at yourself in a looking-glass to see an example of lateral inversion. If you raise your right hand, the image that you see in the glass raises his hand that is on the same side, but as the image faces you it is his left hand. Thus we have a lateral or sideways inversion, and all photographs taken direct suffer in this way. A negative is laterally reversed, but the positive or print made from it, as the two are face to face in making the print, is reversed again and so corrected. A negative looked at through from the back shows the image without lateral inversion.

Anyone who is not familiar with this phenomenon of lateral inversion may find another illustration help to make its character more clear. Take a piece of tracing paper, or the equivalent, and draw on it in ink some design with different sides to it, such as the profile of a person’s face or the letter F. Looking at the side of the paper that you have written on the writing is not reversed, but by turning the paper over and looking at it from the back the design is laterally reversed, the face or the horizontal strokes of the letter point in the opposite direction. Now hold up the paper with its under side to a looking-glass and look at the back of the paper as seen reflected in the glass, and the reversed image will be found to be re-reversed by the reflection and so to appear in its correct position.

This lateral inversion would of course be intolerable in a portrait, as it would represent the person as if he were left-handed, any mark on one side of his face would appear on the other side, his coat would button over the wrong way, his watch and his handkerchief would be in pockets on his right hand side, his hair would be parted on the right instead of the left, and everything would be wrong. This difficulty used to be overcome in making Daguerreotypes by putting a mirror in front of the lens and at an angle with it, and photographing the reflected image instead of the person direct. A reflecting prism was sometimes used, but the principle remains exactly the same. Mirrors and prisms are in constant use at the present day in order to correct lateral inversion in those processes that otherwise would cause the final pictures to suffer from it.

Reverting to the method of making negatives for the purpose of getting prints from them, we find that the use of paper as a support for the sensitive silver compound had many disadvantages. The water-mark, if present, and other variations in its thickness, the impurities and foreign matters that might be present, the possible variations in the sizing of it (that is the addition of substances to render it less absorbent as blotting-paper is), all tended to introduce irregularities. Again, paper is not very transparent and even if impregnated with waxy substances, as was often done, it still left much to be desired in this particular. Glass had been used by Niepce, though not apparently for the sake of getting what we understand as a negative. Sir John Herschel in 1840 used glass, and got his silver salt upon it by putting it at the bottom of a vessel that contained the silver salt suspended in water, and allowing the silver salt to settle down upon it. By carefully removing the plate and drying it, the silver salt adhered sufficiently to permit of the necessary operations, if due care was taken. He found that it was possible to get prints from photographs produced on such plates, though he did not make them especially for use as negatives, but the inconvenience and risk in both the preparation and use of them would preclude them from being generally employed.

Others endeavored to use glass plates instead of paper, but it was not until the nephew of Niepce, Niepce de Saint Victor, in 1848, worked out a method of using a film of albumen to hold the sensitive compound on to the glass, that the production of negatives on glass became a practically useful method. Other substances were tried as well as albumen, but without much success until Frederick Scott Archer published in 1851 a method that he had elaborated of using collodion for this purpose. The collodion process is still in use for certain purposes so that it demands a more detailed consideration.