The prismatic impression on paper spread with the chloride of silver is often very beautifully tinted, the intensity of color varying with the kind of muriate used. Spread paper with muriate of ammonia or baryta and you obtain a range of colors nearly corresponding with the natural hues of the prismatic spectrum. Under favorable circ.u.mstances the mean red ray, leaves a red impression, which pa.s.ses into a green over the s.p.a.ce occupied by the yellow rays. Above this a leaden hue is observed, and about the mean blue ray, where the action is greatest, it rapidly pa.s.ses through brown into black, and through the most refrangible rays it gradually declines into a bluish brown, which tint is continued throughout the invisible rays. At the least refrangible end of the spectrum, the very remarkable phenomenon has been observed, of the extreme red rays exerting a protecting influence, and preserving the paper from that change, which it would otherwise undergo, under the influence of the dispersed light which always surrounds the spectrum.
Not only the extreme red ray exerts this very peculiar property, but the ordinary red ray through nearly its whole length.
In photographic drawing this salt is of the utmost importance. Mr.
Talbot"s application of it will be given hereafter in another portion of this work.
IODIDE OF SILVER--Perfectly pure, undergoes very little change under the influence of light or heat; but if a very slight excess of the nitrate of silver be added it becomes infinitely more sensitive than the chloride.
The spectrum impressed upon paper prepared with a weak solution of the hydriodate of potash presents some very remarkable peculiarities. The maximum of intensity is found at the edge of the most refrangible violet rays, or a little beyond it, varying slightly according to the kind of paper used, and the quant.i.ty of free nitrate of silver present.
The action commences at a point nearly coincident with the mean red of the luminous spectrum, where it gives a dull ash or lead color, while the most refrangible rays impress a ruddy snuff-brown, the change of tint coming on rather suddenly about the end of the blue or beginning of the violet rays of the luminous spectrum. Beyond the extreme violet rays, the action rapidly diminishes, but the darkening produced by these invisible rays, extends a very small s.p.a.ce beyond the point at which they cease to act on the chloride of silver.
In its photographic application, it is, alone, of very little use; but in combination with other reagents it becomes exquisitely sensitive.
With gallic acid and the ferrocyanate of potash it forms two of the most sensitive photographic solutions with which we are acquainted.
These are used in the calotype process.
IODURET OF SILVER.--If upon a plate of polished silver we place a small piece of iodine, and apply the heat of a lamp beneath the plate for a moment, a system of rings is speedily formed. The first ring, which spreading constantly forms the exterior of the circle, is of a bright yellow color; within this, there arises, successively, rings of green, red and blue colors, and then again a fine yellow circle, centred by a greyish spot on the place occupied by the iodine. On exposing these to the light, the outer yellow circle almost instantly changes color, the others slowly, in the order of their position, the interior yellow circle resisting for a long time the solar influence. These rings must be regarded as films of the ioduret of silver, varying, not only in thickness, but in the more or less perfect states of combination in which the iodine and metal are. The exterior circle is an ioduret in a very loose state of chemical agregation; the attractive forces increase as we proceed towards the centre, where a well formed ioduret, or probably a true iodide of silver, is formed, which is acted upon by sunlight with difficulty. The exterior and most sensitive film const.i.tutes the surface of Daguerreotype plates. The changes which these colored rings undergo are remarkable; by a few minutes exposure to sunlight, an inversion of nearly all the colors takes place, the two first rings becoming a deep olive green; and a deep blue inclining to black.
The nature of the change which the ioduret of silver undergoes on Daguerreotype plates, through the action of light, Mr. Hunt considers to be a decided case of decomposition, and cites several circ.u.mstances in proof of his position. These with other facts given by Mr. Hunt in his great work on the Photographic art, but to voluminous to include in a volume of the size to which I am obliged to confine myself, should be thoroughly studied by all Daguerreotypists.
PRISMATIC a.n.a.lYSIS.--The most refrangible portion of the spectrum, (on a Daguerreotype plate) appears, after the plate has been exposed to the vapor of mercury, to have impressed its colors; the light and delicate film of mercury, which covers that portion, a.s.suming a fine blue tint about the central parts, which are gradually shaded off into a pale grey; and this is again surrounded by a very delicate rose hue, which is lost in a band of pure white. Beyond this a protecting influence is powerfully exerted; and notwithstanding the action of the dispersed light, which is very evident over the plate, a line is left, perfectly free from mercurial vapor, and which, consequently, when viewed by a side light, appears quite dark. The green rays are represented by a line of a corresponding tint, considerably less in size than the luminous green rays. The yellow rays appear to be without action, or to act negatively, the s.p.a.ce upon which they fall being protected from the mercurial vapor; and it consequently is seen as a dark band. A white line of vapor marks the place of the orange rays. The red rays effect the sensitive surface in a peculiar manner; and we have the mercurial vapor, a.s.suming a molecular arrangement which gives to it a fine rose hue; this tint is surrounded by a line of white vapor, shaded at the lowest extremity with a very soft green. Over the s.p.a.ce occupied by the extreme red rays, a protecting influence is again exerted; the s.p.a.ce is retained free from mercurial vapor and the band is found to surround the whole of the least refrangible rays, and to unite itself with the band which surrounds the rays of greatest refrangibility. This band is not equally well defined throughout its whole extent. It is most evident from the extreme red to the green; it fades in pa.s.sing through the blue, and increases again, as it leaves the indigo, until beyond the invisible chemical rays it is nearly as strong as it is at the calorific end of the spectrum.
Images on Daguerreotype plates which have been completely obliterated by rubbing may be restored, by placing it in a tolerably strong solution of iodine in water.
BROMIDE OF SILVER.--This salt, like the iodide, does not appear to be readily changed by the action of light; but when combined with the nitrate of silver it forms a very sensitive photographic preparation.
Paper prepared with this salt, blackens over its whole extent with nearly equal intensity, when submitted to the prismatic spectrum. The most characteristic peculiarity of the spectrum is its extravagant length. Instead of terminating at the mean yellow ray, the darkened portion extends down to the very extremity of the visible red rays. In tint it is pretty uniformly of a grey-black over its whole extent, except that a slight fringe of redness is perceptible at the least refracted end. Beyond the red ray, an extended s.p.a.ce is protected from the agency of the dispersed light, and its whiteness maintained; thus confirming the evidence of some chemical power in action, over a s.p.a.ce beyond the luminous spectrum, which corresponds with the rays of the least refrangibility.
This salt is extensively used in photographic drawing.
PREPARATIONS OF GOLD.--Chloride of Gold, freed from an excess of acid is slowly changed under the action of light; a regularly increasing darkness taking place until it becomes purple, the first action of the light being to whiten the paper, which, if removed from the light at this stage, will gradually darken and eventually develope the picture.
This process may be quickened by placing the paper in cold water.
Chloride of gold with nitrate of silver gives a precipitate of a yellow brown color. Paper impregnated with the acetate of lead, when washed with perfectly neutral chloride of gold, acquires a brownish-yellow hue. The first impression of light seems rather to whiten than darken the paper, by discharging the original color, and subst.i.tuting for it a pale greyish tint, which by slow degrees increases to a dark slate color; but if arrested, while yet, not more than a moderate ash grey, and held in a current of steam, the color of the parts acted upon by light--and of that only--darkens immediately to a deep purple.
Here I must leave the subject of the action of light upon metalic compounds--referring to Mr. Hunts work for any further information the student may desire on the other metals--as I find myself going beyond my limits. I cannot, however, entirely dismiss the subject without giving a few examples of the action of light on the juices of plants, some of which produce very good photographic effect.
CORCHORUS j.a.pONICA--The juice of the flowers of this plant impart a fine yellow color to paper, and, so far as ascertained, is the most sensitive of any vegetable preparation; but owing to its continuing to change color even in the dark, photographic images taken on paper prepared with it soon fade out.
WALL FLOWER.--This flower yields a juice, when expressed with alcohol, from which subsides, on standing, a bright yellow finely divided faecula, leaving a greenish-yellow transparent liquid, only slightly colored supernatant. The faecula spreads well on paper, and is very sensitive to light, but appears at the same time to undergo a sort of chromatic a.n.a.lysis, and to comport itself as if composed of two very distinct coloring principles, very differently affected. The one on which the intensity and sub-orange tint of the color depends, is speedily destroyed, but the paper is not thereby fully whitened. A paler yellow remains as a residual tint, and this on continued exposure to the light, slowly darkens to brown. Exposed to the spectrum, the paper is first reduced nearly to whiteness in the region of the blue and violet rays. More slowly, an insulated solar image is whitened in the less refrangible portion of the red. Continue the exposure, and a brown impression begins to be percieved in the midst of the white streak, which darkens slowly over the region between the lower blue and extreme violet rays.
THE RED POPPY yields a very beautiful red color, which is entirely destroyed by light. When perfectly dried on paper the color becomes blue. This blue color is speedily discharged by exposure to the sun"s rays, and papers prepared with it afford very interesting photographs.-- Future experiments will undoubtedly more fully develope the photogenic properties of flowers, and practically apply them.
Certain precautions are necessary in extracting the coloring matter of flowers. The petals of fresh flowers, carefully selected, are crushed to a pulp in a mortar, either alone or with the addition of a little alcohol, and the juice expressed by squeezing the pulp in a clean linen or cotton cloth. It is then to be spread upon paper with a flat brush, and dried in the air. If alcohol be not added, it must be applied immediately, as the air changes or destroys the color instantly.
Most flowers give out their coloring matter to alcohol or water--but the former is found to weaken, and in some cases to discharge altogether these colors; but they are in most cases restored in drying.
Paper tinged with vegetable colors must be kept perfectly dry and in darkness.
To secure an eveness of tint on paper it should be first moistened on the back by sponging, and blotting off with bibulous paper. It should then be pinned on a board, the moist side downwards, so that two of its edges--the right and lower ones--project a little over those of the board. Incline the board twenty or thirty degrees to the horizon, and apply the tincture with a brush in strokes from right to left, taking care not to go over the edges which rests on the board, but to pa.s.s clearly over those that project; and also observing to carry the tint from below upwards by quick sweeping strokes, leaving no dry s.p.a.ces between them. Cross these with other strokes from above downwards, leaving no floating liquid on the paper. Dry as quickly as possible, avoiding, however, such heat as may injure the tint.
CHAP. IV.
A FEW HINTS AND SUGGESTIONS TO DAGUERREOTYPISTS.
There are very few who may not be capable of practising the Photographic art, either on paper, or metalic plates--but, like all other professions, some are more clever in its various processes than others.
Impatience is a great drawback to perfect success, and combined with laziness is a decided enemy. Besides this, no one can excel in Photography who does not possess a natural taste for the fine arts, who is not quick in discerning grace and beauty--is regardless of the principles of perspective, foreshortening and other rules of drawing, and who sets about it merely for the sake of gain--without the least ambition to rise to the first rank, both in its practice and theory.
There is no profession or trade in which a slovenly manner will not show itself, and none where its effects will be more apparent than this.
In order to be great in any pursuit, we must be ourselves, and keep all things, in order. In your show and reception rooms, let neatness prevail; have your specimens so placed--leaning slightly forward--as to obtain the strongest light upon them, and at the same time prevent that gla.s.siness of appearance which detracts so materially from the effect they are intended to produce. If possible, let the light be of a north-western aspect, mellowed by curtains of a semitransparent hue.
Your show-cases, at the door, should be kept well cleaned. I have often been disgusted while attempting to examine portraits in the cases of our artists, at the greasy coating and marks of dirty fingers upon the gla.s.s and frame enclosing them. Believe it, many a good customer is lost for no other reason.
In your operating room, dust should be carefully excluded. It should be furnished with nothing apt to collect and retain dust; a carpet is therefore not only a useless article, but very improper. A bare floor is to be prefered; but if you must cover it use matting. There is no place about your establishment where greater care should be taken to have order and cleanliness; for it will prevent many failures often attributed to other causes. "A place for every thing, and every thing in its place," should be an absolute maxim with all artists. Do not oblige the ladies, on going away from your rooms, to say--"That H. is a slovenly man; see how my dress is ruined by sitting down in a chair that looked as if it had just come out of a porter house kitchen and had not been cleaned for six months."
In choosing your operating room, obtain one with a north-western aspect, if possible; and either with, or capable of having attached, a large skylight. Good pictures may be taken without the sky-light, but not the most pleasing or effective.
A very important point to be observed, is to keep the camera perfectly free from dust. The operator should be careful to see that the slightest particle be removed, for the act of inserting the plate-holder will set it in motion, if left, and cause those little black spots on the plate, by which an otherwise good picture is spoiled. The camera should be so placed as to prevent the sun shining into the lenses.
In taking portraits, the conformation of the sitter should be minutely studied to enable you to place her or him in a position the most graceful and easy to be obtained. The eyes should be fixed on some object a little above the camera, and to one side--but never into, or on the instrument, as some direct; the latter generally gives a fixed, silly, staring, scowling or painful expression to the face. Care should also be taken, that the hands and feet, in whatever position, are not too forward or back ward from the face when that is in good focus.
If any large surface of white is present, such as the shirt front, or lady"s handkerchief, a piece of dark cloth (a temporary bosom of nankeen is best,) may be put over it, but quickly withdrawn when the process is about two thirds finished.
A very pleasing effect is given to portraits, by introducing, behind the sitter, an engraving or other picture--if a painting, avoid those in which warm and glowing tints predominate. The subject of these pictures may be applicable to the taste or occupation of the person whose portrait you are taking. This adds much to the interest of the picture, which is otherwise frequently dull, cold and inanimate.
Mr. J. H. Whitehurst of Richmond, Va., has introduced a revolving background, which is set in motion during the operation, and produces a distinctness and boldness in the image not otherwise to be obtained.
The effect upon the background of the plate is equally pleasing; it having the appearance of a beautifully clouded sky.
In practising Photographic drawing on paper, the student must bear in mind that it is positively essential, to secure success in the various processes, to use the utmost precaution in spreading the solutions, and washes from the combination of which the sensitive surfaces result.
The same brush should always be used for the same solution, and never used for any other, and always washed in clean water after having been employed. Any metalic mounting on the brushes should be avoided, as the metal precipitates the silver from its solution. The brushes should be made of camels or badger"s hair and sufficiently broad and large to cover the paper in two or three sweeps; for if small ones be employed, many strokes must be given, which leave corresponding streaks that will become visible when submitted to light, and spoil the picture.
These few preliminary hints and suggestions, will, I trust, be of some service to all who adopt this pleasing art as a profession; and will, with a due attention to the directions given in the practical working of the Daguerreotype, Calotype, etc., ensure a corresponding measure of success.
CHAP. V.
DAGUERREOTYPE APPARATUS.
The entire Daguerreotype process is comprised in seven distinct operations; viz:
1.--Cleaning and polishing the plate.
2.--Applying the sensitive coating.
3--Submitting the plate to the action of light in the camera.
4.--Bringing out the picture; in other words rendering it visible.