Joshua King Ingalls
THE employment of light as an agent in copying, or drawing, was suggested as early as the commencement of the present century, by Mr. Wedgewood, and Sir Humphrey Davy. If a piece of paper be dipped into a weak solution of nitrate of silver, and carefully dried, while excluded from the light, it retains its original color; but on exposure, gradually becomes dark, and even black. A paper thus prepared, placed behind a transparent painting, when held up to the light, would copy exactly the light and shades, yet in reversed order
What was light on the original, will be dark on the copy, and what was dark, will be light. If this copy be now copied, it will present the same appearance as the original. But as the whole surface thus prepared would become black by subsequent exposure to the light, a wash of hyposulphate of soda is employed, which removes the unaltered nitrate, leaving the image untouched. The chloride of silver is said to be still more susceptible of the influence of light, than the mere nitrate. Many ingenious and important experiments have been made by Mr. Talbot and Sir John Herschel of England, and Mr. A. Taylor, of this country.
But it was not until Daguerre, an eminent French artist, succeeded in copying the images from the lens of the camera obscura, that this method justly took rank among the Arts. By his process the objects are lighted as in nature, and with all the sparkling variety of effect which light sheds on all terrestrial things.
With the single exception of color, these pictures mirror forth Nature, herself. The qualities of objects are clearly expressed, so that the materials of dress or ornament could not be mistaken. Where landscapes are’ taken, the intensity of tone in the foreground is softened by the aerial effects in the distance, and so exact is the copy that on examination by a microscope, the minutest objects appear as perfect as those of greater magnitude. Altogether the discovery may be regarded as the most important for the fine arts made in modern times.
As before stated, the Daguerreotype is taken from the image in a camera, constructed especially for this purpose. It inverts the image, however; but in portraits, this is of little consequence. In landscapes, or whenever this difficulty requires to be obviated, a mirror of Speculum metal is attached, which reinverts the image and makes the picture appear as in nature. In the place of paper and nitrate of silver, the silvered surface of a metallic plate is employed, covered with a film from the vapor of iodine. The process is dependent on the principle that light accelerates certain chemical changes, which is a well known fact. The plates are usually made of copper, and plated with silver on one side. This side is thoroughly polished with rotten stone, Tripoli, and buff of buck-skin; then the plate is introduced over a bath of dry iodine, from which all light is excluded, for a minute or more, according to the strength of the vapor,—which is subject to variation by different temperature and other causes. It requires to be kept in contact with this vapor until it assumes a rich straw or gold color. It is then introduced over a bath, composed of a preparation of Bromine, and called “Quick Stuff,” from its property of accelerating the process, where it is kept until it assumes a crimson or purple tinge. Then it is passed again over the iodine a few seconds, and immediately inclosed in a dark frame which is provided with a slide over the prepared surface, and fitted to the proper place in the camera. 
The lens having first been arranged to bring the object in focus upon the place the late is to occupy, it is then put into the camera, and the slide being withdrawn, the action begins. The sitting requires from two or three seconds to a minute, according to the quality of the lens, strength of light, and the rapidity with which the chemicals act. In taking children, it is desirable to facilitate the process as much as possible; but such rapid action is more likely to fail. When, in the estimation of the operator, the exposure has been sufficiently prolonged, the slide is replaced, the frame containing the plate taken out, and the plate itself transferred without exposure to the light, to a mercury bath, heated to 170 degrees, Fahrenheit. It is kept there a short space, when the process is complete.
Much depends on the skill with which each step is taken. If any one be omitted, or badly executed, there is no picture. Even when the picture is well taken there is danger of spoiling it, in the subsequent washing and gilding. When taken from the mercury bath, the plate is discolored with the chemicals. This is washed off with a solution of hyposulphate of soda, and afterward;, with distilled water. But the picture would then be erased by the slightest touch. A method of gilding has been adopted, which renders it fixed and permanent, and deepens the effect. This is done by dissolving chloride of gold in a solution of hyposulphate of soda, and covering the surface of the picture with it, while the plate is held over a spirit lamp until it approaches the boiling point. It is then washed off with distilled water, and is ready for the case.
Some operators employ a galvanic battery, and thus apply a fresh coating of silver to the plates every time they are cleaned, and immediately before coating with the chemicals. This evidently softens the picture, but, in the estimation of many, does not improve it. It is also customary to color the pictures slightly after they are gilded, though good connoisseurs do not approve of this.
The philosophy of the operation appears to be simply, that iodine will not corrode silver readily, unless exposed to the chemical rays of light. But as any illuminated object reflects a varied degree of light from each point, or color, so the action on the plate corresponds to the amount of light thrown from the object upon it. The address to stop the operation at that point, when the strongest light has exhausted the corrosive power of the film, and the weakest has made the deepest shaded points sufficiently distinct, is especially necessary in the management of the camera. And judgment alone can avail, because all these operations must be carried on in the dark, where no eye can penetrate. But the corrosion of the metal does not make a picture. Little or nothing could be discerned by the eye after the plate is taken from the camera, until it is exposed to the mercury. The vapor of this bath combines in infinitely small particles with the corroded substance of the silver, but does not combine with the film. This gives the color of mercury, or white, to the most deeply corroded parts, and leaves the others dark.
The cheap rate at which daguerreotypes can be afforded, has made them common among all classes, and thus tended to elevate the taste of the people to a degree which never could have been done by expensive ns paintings or other methods of art. The discovery is to be looked on, as one of the means for promoting refinement among the masses.
The blue, violet, and red, are the principal chemical rays. Light and shade, where these colors are contrasted with green, yellow, or orange, or even white, will not appear in the picture as in the object. A person sitting for a picture with a dress where blue and white were strongly contrasted, would be surprised to find no contrast at all in the likeness, and if contrasted with orange or yellow for the lighter shade, to find the shades reversed, the light, dark, and the dark, light. For this reason clear, blue eyes appear much lighter than they really are, while olive colored appear much darker. The dress for  sitting if any other color than black is preferred, should be chosen with reference to the complexion. Dark, or sallow complexions should have black, and if contrast is desired let it be white. Persons of clear complexion may be taken in almost any color they choose, only when contrasts are sought, let the chemical rays be light, and the inactive dark; they will not then be disappointed in the results.