The History and Practice of the Art of Photography [10]
of silver, which is a white precipitate formed by adding chloride of sodium (common salt) to a solution of nitrate of silver, be exposed to diffused light, it speedily assumes a violet tint, and ultimately becomes nearly black. With iodide of silver, bromide of silver, ammonio-nitrate of silver, and other salts of this metal, the result will be much the same.
Some bodies, which under the influence of light, undergo chemical changes, have the power of restoring themselves to their original condition in the dark. This is more remarkably displayed in the iodide of platinum, which readily recieves a photogenic image by darkening over the exposed surfaces, but speedily loses it by bleaching in the dark. The ioduret of Daguerre's plate, and some other iodides, exhibit the same peculiarity--This leads us to the striking fact, that bodies which have undergone a change of estate under the influence of day-light have some latent power by which they can renovate themselves. Possibly the hours of night are as necessary to inanimate nature as they are to the animate. During the day, an excitement which we do not heed, unless in a state of disease, is maintained by the influence of light and the hours of repose, during which the equilibrium is restored, are absolutely necessary to the continuance of health.
Instead of a few chemical compounds of gold and silver, which at first were alone supposed to be photographic, we are now aware that copper, platinum, lead, nikel, and indeed, probably all the elements, are equally liably to change under the sun's influence. This fact may be of benefit to engravers, for if steel can be made to take photographic impressions, the more laborious process of etching may be dispensed with. In fact, in the latter part of this work, a process is described for etching and taking printed impressions from Daguerreotype plates. As yet this process has produced no decided beneficial results-- but future experiments may accomplish some practical discovery of intrinsic value to the art of engraving.
A very simple experiment will prove how essential light is to the coloring of the various species comprising the vegetable and animal kingdoms. If we transplant any shrub from the light of day into a dark cellar, we will soon see it lose its bright green color, and become perfectly white.
Another effect of light is that it appears to impart to bodies some power by which they more readily enter into chemical combination with others. We have already said that chlorine and hydrogen, if kept in the dark, will remain unaltered; but if the chlorine alone be previously exposed to the sun, the chlorine thus solarised will unite with the hydrogen in the dark. Sulphate of iron will throw down gold or silver from their solutions slowly in the dark; but if either solution be first exposed to sunshine, and the mixture be then made, in the dark, the precipitation takes place instantly. Here is again, evidence of either an absorption of some material agent from the sunbeam, or an alteration in the chemical constitution of the body. It was from understanding these principles and applying them that philosophers were enabled to produce the Calotype, Daguerreotype, &c. For the effects and action of light on the camera, see Chapter V.
Some advances have been made towards producing Photographic impressions in color--the impossibility of which some of our best and oldest artists have most pertinaciously maintained. The colored image of the spectrum has been most faithfully copied, ray for ray, on paper spread with the juice of the Cochorus Japonica, (a species of plant) and the fluoride of silver; and on silver plate covered with a thin film of chloride. The day may be still remote when this much to be desired decideratum shall be accomplished in portrait taking; but I am led to hope that future experiments may master the secret which now causes it to be looked upon, by many, as an impossibility.
That great advantages have resulted, and that greater still will result from the discovery of the Photographic art, few will
Some bodies, which under the influence of light, undergo chemical changes, have the power of restoring themselves to their original condition in the dark. This is more remarkably displayed in the iodide of platinum, which readily recieves a photogenic image by darkening over the exposed surfaces, but speedily loses it by bleaching in the dark. The ioduret of Daguerre's plate, and some other iodides, exhibit the same peculiarity--This leads us to the striking fact, that bodies which have undergone a change of estate under the influence of day-light have some latent power by which they can renovate themselves. Possibly the hours of night are as necessary to inanimate nature as they are to the animate. During the day, an excitement which we do not heed, unless in a state of disease, is maintained by the influence of light and the hours of repose, during which the equilibrium is restored, are absolutely necessary to the continuance of health.
Instead of a few chemical compounds of gold and silver, which at first were alone supposed to be photographic, we are now aware that copper, platinum, lead, nikel, and indeed, probably all the elements, are equally liably to change under the sun's influence. This fact may be of benefit to engravers, for if steel can be made to take photographic impressions, the more laborious process of etching may be dispensed with. In fact, in the latter part of this work, a process is described for etching and taking printed impressions from Daguerreotype plates. As yet this process has produced no decided beneficial results-- but future experiments may accomplish some practical discovery of intrinsic value to the art of engraving.
A very simple experiment will prove how essential light is to the coloring of the various species comprising the vegetable and animal kingdoms. If we transplant any shrub from the light of day into a dark cellar, we will soon see it lose its bright green color, and become perfectly white.
Another effect of light is that it appears to impart to bodies some power by which they more readily enter into chemical combination with others. We have already said that chlorine and hydrogen, if kept in the dark, will remain unaltered; but if the chlorine alone be previously exposed to the sun, the chlorine thus solarised will unite with the hydrogen in the dark. Sulphate of iron will throw down gold or silver from their solutions slowly in the dark; but if either solution be first exposed to sunshine, and the mixture be then made, in the dark, the precipitation takes place instantly. Here is again, evidence of either an absorption of some material agent from the sunbeam, or an alteration in the chemical constitution of the body. It was from understanding these principles and applying them that philosophers were enabled to produce the Calotype, Daguerreotype, &c. For the effects and action of light on the camera, see Chapter V.
Some advances have been made towards producing Photographic impressions in color--the impossibility of which some of our best and oldest artists have most pertinaciously maintained. The colored image of the spectrum has been most faithfully copied, ray for ray, on paper spread with the juice of the Cochorus Japonica, (a species of plant) and the fluoride of silver; and on silver plate covered with a thin film of chloride. The day may be still remote when this much to be desired decideratum shall be accomplished in portrait taking; but I am led to hope that future experiments may master the secret which now causes it to be looked upon, by many, as an impossibility.
That great advantages have resulted, and that greater still will result from the discovery of the Photographic art, few will