The Chemistry of Photography

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Scovill & Adams, 1892 - Photographic chemistry - 426 pages
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Page 377 - I have now briefly mentioned appears to me to partake of the character of the marvellous, almost as much as any fact which physical investigation has yet brought to our knowledge. The most transitory of things, a shadow, the proverbial emblem of all that is fleeting and momentary, may be fettered by the spells of our
Page 375 - I read it, already discovered a method of overcoming this difficulty, and of fixing the image in such a manner that it is no more liable to injury or destruction. In the course of my experiments directed to that end, I have been astonished at the variety of effects which I have found produced by a very limited number of different processes when combined in various ways; and also at the length of time which sometimes elapses before the full effect of these manifests itself with certainty. For I have...
Page 376 - ... spontaneous change; or, if they are so, still it does not follow that that change will now tend to assimilate them to each other. In case of their remaining dissimilar, the picture will remain visible, and therefore our object will be accomplished. If it should be asserted that exposure to sunshine would necessarily reduce the whole to one uniform tint, and destroy the picture, the onus probandi evidently lies on those who make the assertion. If we designate by the letter A the exposure to the...
Page 376 - On one of these more especially I have made numerous experiments; the other I have comparatively little used, because it appears to require more nicety in the management. It is, however, equal, if not superior, to the first in brilliancy of effect. This chemical change, which I call the preserving process, is far more effectual than could have been anticipated. The paper, which had previously been so sensitive to light, becomes completely insensible to it, insomuch that I am able to show the Society...
Page 259 - The portion covered by the object retains the original bright yellow tint, which it had before exposure, and the object is thus represented yellow upon an orange ground, there being several gradations of shade, or tint, according to the greater or less degree of transparency in the different parts of the object. In this state, of course, the drawing though very beautiful is evanescent. To fix it, all that is required is careful immersion in water, when it will be found that those portions of the...
Page 372 - Nothing but a method of preventing the unshaded parts of the delineation from being colored by exposure to the day, is wanting to render this process as useful as it is elegant.
Page 312 - ... alternately changed from a white positive to a black negative many times in succession, and very often with improvement. Thus, by the above process, a most perfect white positive or a deep black negative is produced, quite distinct from each other. In the first part of this after-process it will be observed that the effect of this bi-chloride of mercury solution is to deepen the shades of the picture, and this peculiarity can be made available to strengthen a faint image, by taking the precaution...
Page 203 - ... impressions exist. The forms of the future picture remain still invisible. The next operation then is to disengage the shrouded imagery, and this is accomplished by a solvent, consisting of one part by volume of essential oil of lavender, and ten of oil of white petroleum. Into this liquid the exposed tablet is plunged, and the operator observing it by reflected light, begins to perceive the images of the objects to which it had been exposed, gradually unfolding their forms. The plate is then...
Page 312 - The picture being thoroughly washed in plenty of water, after fixing with hypo-sulphite of soda, is treated in the following manner. Prepare a saturated solution of bi-chloride of mercury in muriatic acid. Add one part of this solution to six of water. Pour a small quantity of it over the picture at one corner, and allow it to run evenly over the glass. It will be found immediately to deepen the tones of the picture considerably, and the positive image will almost disappear ; presently, a peculiar...
Page 386 - Requisites: ist, very susceptible paper ; ind, very perfect camera ; 3rd, means of arresting further action. Tried hyposulphite of soda to arrest the action of light by washing away all the chloride of silver or other silvering salt ; succeeds perfectly. Papers half acted on, half guarded from the light by covering with pasteboard, were •withdrawn from sunshine, sponged over with hyposulphite, then washed in pure water, dried, and again exposed. The darkened half remained dark, the white half white,...

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