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The photographic news
- Bandzählung
- 27.1883
- Erscheinungsdatum
- 1883
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- Englisch
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- Hochschule für Grafik und Buchkunst Leipzig
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- Hochschule für Grafik und Buchkunst Leipzig
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- Bandzählung
- No. 1276, February 16, 1883
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Zeitschrift
The photographic news
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Band
Band 27.1883
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- Titelblatt Titelblatt I
- Register Index III
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Band
Band 27.1883
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Aatent Eutelligence. Patent Granted in France. 150,479. CovE, of Nantes, for “ A slide frame for photographs.” —Dated 9th August, 1882. Class 18. Specification Published during the week. 3491. E. G. Colton, for “ Apparatus for producing photographic images.”—A communication from W. Kurtz. This invention [has reference to an improved method of and apparatus for producing photographic images in such a manner that the lights and shadows are forced to move during exposure, over the face of the sitter, without the necessity of any change in the usual appliances of a photographic studio, and by which over-exposed high lights and under-exposed shadows are entirely dispensed with, a thoroughly-exposed negative made in a very short time and without a reflector, and an artistic picture produced even by inexperienced operators with little extra labour and expense. This process has the further advantage that retouching is to a large degree dispensed with, owing to the moving of the shadows and high lights during exposure, whereby they are made to come out soft and fleshy, and in a more natural manner. The invention consists of a method of producing photographic images by which the object to be photographed and the photographic apparatus are simul taneously moved during exposure, so that the lights and shadows are forced to pass over the object; and it consists, secondly, of a movable platform supporting the object to be photographed and the camera, the said platform being provided with means for being moved through a suitable distance during the time of exposure, and with a rotary platform for turning the sitter or object. By this improved method and apparatus the photographic images are produced by the same appliances as have been used heretofore either in the wet or dry process, with this difference, that the camera and sitter or other object are placed on a platform which is moved during exposure, so that the lights and shadows are forced to move over the face of the sitter, whereby a more artistic distribution of light and shade and a much better picture are produced. The operator is by this method and apparatus enabled to expose the object first in a half-light and turn it then into a strong light, which will give him the high lights last, so that he becomes thereby complete master of his light without the trouble and delay of adjusting curtains and bliuds. Pictures can also be taken in a shorter time, with very little retouching, and furnish better portraits, which have greater softness and rotundity, and are a a more faithful reproduction of nature, than the pictures with strong high lights and shadows obtained by the ordinary method hitherto in use. Having now described the nature of the said invention as communicated to me from abroad, and in what manner the same is to be performed, I would have it understood that what I desire to secure by Letters Patent on behalf of the said William Kurtz is:—1. The herein-described improved method of producing photographic images consisting in moving the camera and sitter or object simultaneously during exposure, whereby the various lights and shadows are made to pass over the object being photographed, as set forth. 2. The improved combination of apparatus for producing photographic images, consisting of a movable main platform, which is rotated on a centre pivot in a socket on the floor (or otherwise suitably pivoted), a rotary platform mounted on one end of the main platform for turning the person or object to be photographed, and a camera at the other end, substantially as described. TWELVE ELEMENTARY LESSONS ON SILVER PRINTING. (Lesson III.—Sensitizing. If we place out in daylight a piece of albumenized paper as prepared in the last chapter, no change will take place, because the salt therein contained does not darken when exposed to light. If we immerse or float the paper on a solution of nitrate of silver, a chemical change will take place in the composi tion of the salt contained in the paper. The ammonium and barium chloride will lose their chlorine ; the silver, having a greater affinity for chlorine than either the ammonium or barium, will attract all the chlorine to itself in preference to the nitric acid previously in combination with it; we shall, therefore, have a compound of silver formed, called chloride of silver, together with an organic compound called albuminate of silver ; the nitric acid disengaged from the silver combines with the ammonium and barium. These salts being more or less inert, we need only follow the silver chloride, the salt which darkens in the light. Float a piece of albumenized paper on a solution of nitrate of silver, performing the operation in a yellow or orange-coloured light; no apparent difference will have taken place in the paper. Expose a pcrtion of it to the daylight, leaving a part of it covered with some opaque substance; the ex posed portion will gradually turn grey, then purple, after wards deeper, until finally it reaches a dark copper colour of bronzed hue, beyond which no further change is seen to take place. Now what has happened ? The action of the light has changed the chloride of silver into a sub-chloride, giving off chlorine gas. Silver sub-chloride consists of two equations of silver to one of chlorine. Previous to exposure, the compound may be said to represent 2AgCl ; after exposure, it would repre sent Ag:C1+Cl. As a matter of fact, organic compounds and free nitrate of silver are always present besides. Having touched on the salient chemical points of printing, we will now devote a little time to the practice of it. Make up the following solution:— Ra-crystallized nitrate of silver ... 8 ounces Soft water ... ... 80 ounces When dissolved, filter through Swedish filtering paper or a piece of clean sponge pressed tightly into the neck of the funnel; this solution is named the sensitizing silver bath, or exciting bath. Test the solution for acidity by means of a piece of litmus paper. Should the colour of the paper change from blue and become slightly reddish, it indicates that free nitric acid is present, which should be neutralized by means of sodic carbonate. A good plan is to have two bottles for the bath ; one bottle for pouring into when sensitizing is finished, in which a little sodic carbonate is always kept to insure the bath being neutral ; and the other bottle should be used for filtering into only (see R in diagram Lesson I.). The above quantity of solution will be found enough to float whole sheets of paper, and sufficiently strong to coagulate the albumen perfectly. When the proportion of silver is much below thirty grains per ounce, and neutral or slightly alkaline, there is a great tendency for the albumen to leave the paper ; this is known by dull lines and patches on the paper, also a slightly opalescent scum floating on the bath ; the effect is termed stripping. The dish employed for sensitizing should not be used for any other purpose. The require ments are that it should be flat and perfectly clean. When porcelain dishes have been used a short time, the enamel or glaze cracks all over, the dish thereby becoming useless for the purpose. Ebonite dishes of large size are seldom flat when new, and warp very much after a little wear, there fore a strong wooden frame of pine or teak, with a plate glass bed, seems to last better than anything else. The wood should be well rubbed with solid paraffin, which has the property of completely resisting the action of nitrate of silver. Such a dish, well made, will last a lifetime. A glass rod may be attached to the end of such a dish to drag the paper over, which not only allows of quicker drying, but prevents waste. Sensitizing.—Having dusted the dish, pour out the solu tion to the depth of half an inch equally all over the vessel > brush the surface of the paper with a large flat camel-hair brush; lay the paper steadily (albumenized side downwards) on the surface of the sensitizing bath in such a manner that air-bubbles are not formed, neither the silver allowed to touch the back ; this may be accomplished by floating in the manner described in the last chapter on albumenizing: As soon as the paper has been laid down, it should be lifted by means of a glass rod at one of the corners, and examined i if the operation has been successful, there will be no air-
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