By a slight inclination of the plate the fluid is made to flow towards the corner marked 1, in the above diagram, until it nearly touches the thumb by which the glass is held: from corner 1 it is passed to corner 2, held by the forefinger; from 2 to 3, and lastly, the excess poured back into the bottle from the corner marked No. 4. It is then to be held vertically over the bottle for a moment, until it nearly ceases to drip, and then, by raising the thumb a little, the direction of the plate is changed, so as to cause the diagonal lines to coalesce and produce a smooth surface. The operation of coating a plate with Collodion must not be done hurriedly, and nothing is required to ensure success but steadiness of hand and a sufficiency of the fluid poured in the first instance upon the plate.

In coating larger plates, the pneumatic holder, which fixes itself by suction, will be found the most simple and useful.

The Proper Time for immersing the Film in the Bath.—After exposing a layer of Collodion to the air for a short time, the greater part of the Ether evaporates, and leaves the Pyroxyline in a state in which it is neither wet nor dry, but receives the impression of the finger without adhering to it. Photographers term this setting, and when it takes place it is a sign that the time has come for submitting it to the action of the Bath.

If the film be lowered into the Nitrate before it has set, the effect is the same as that produced by adding Water to Collodion. The Pyroxyline is precipitated in part, and consequently there are cracks, and the developer will not always run up to the edge of the film. On the other hand, if it be allowed to become too dry, the Iodide of Silver does not form perfectly, and the film, on being washed and brought out to the light, exhibits a peculiar iridescent appearance, and is paler in some parts than in others.

No rule can be given as to the exact time which ought to elapse: it varies with the temperature of the atmosphere, and with the proportions of Ether and of Pyroxyline; thin Collodion containing but little Alcohol requiring to be immersed more speedily. Twenty seconds in the common way, or ten seconds in hot weather, will be found an average time.

When the plate is ready, rest it upon the glass dipper, Collodion side uppermost, and lower it into the solution by a slow and steady movement: if any pause be made, a horizontal line corresponding to the surface of the liquid will be formed. Then place the cover upon the vertical trough[35] and darken the room, if this has not already been done. As the presence of white light does no injury to the plate previous to its immersion in the Bath, it is not necessary to exclude it during the time of coating with Collodion.

When the plate has remained in the solution about twenty seconds, lift it partially out two or three times, in order to wash away the Ether from the surface. An immersion of one minute to a minute and a half will usually be sufficient; or two minutes in cold weather, and with Collodion containing but little Alcohol. Continue to move the plate until the liquid flows off in a uniform sheet, when the decomposition may be considered to be sufficiently perfect. The principal impediment in this part of the process lies in the difficulty with which Ether and Water mix together, which causes the Collodion surface on its first immersion to appear oily and covered with streaks. By gentle motion the Ether is washed away, and a smooth and homogeneous layer obtained.

The plate is next removed from the dipper, and held vertically in the hand for a few seconds upon blotting paper, to drain off as much as possible of the solution of Nitrate of Silver.[36] It is then wiped on the back with filtering-paper, placed in a clean and dry slide, and is ready for the Camera.

The amateur is strongly recommended not to proceed to take pictures in the Camera until by a little practice he has succeeded in producing a perfect film which is uniform in every part and will bear inspection when washed and brought out to the light.

It should, if properly prepared, present the following appearance:—Smooth and uniform, both by reflected and transmitted light; free from wavy lines or markings such as would be caused by a glutinous Pyroxyline, and from opaque dots due to small particles of dust or Iodide of Silver in suspension in the Collodion.

The evidences of a too rapid immersion in the Bath are sought for on the side of the plate from which the Collodion was poured off. This part remains wet longer than the other, and always suffers the most; horizontal cracks or marks resembling vegetation are seen, each of which would cause an irregular action of the developing fluid. On the other hand, the upper part of the plate must be examined for the pale colour characteristic of a film which had become too dry before immersion, since the Collodion is thinner at that point than at any other.

EXPOSURE OF THE PLATE IN THE CAMERA.

After the plate has been rendered sensitive, it should be exposed and developed with all convenient despatch; the intensity of the Negatives being, with some Collodion, materially lessened by neglecting this point (see p. 100).

Ascertain that the joints of the Camera are tight in every part—that the sensitive plate, when placed in the slide, falls precisely in the same plane as that occupied by the ground glass—and that the chemical and visual foci of the Lens accurately correspond.[37]

Supposing the case of a portrait, next proceed to arrange the sitter as nearly as possible in a vertical position, that every part may be equidistant from the lens. Then, an imaginary line being drawn from the head to the knee, point the Camera slightly downwards, so that it may stand at right angles to the line. If this point be neglected the figure will be liable to be distorted in a manner presently to be shown (p. 228).

In order to succeed well with portraits, the sitter should be illuminated by an even, diffused light falling horizontally. A vertical light causes a deep shadow on the eyes and makes the hair appear grey: it must therefore be cut off by a curtain of blue or white calico suspended over the head. The direct rays of the sun are generally to be avoided, as causing too great a contrast of light and shade. This is a point on which the operator must exercise his judgment. With a feeble Collodion, a better Negative picture may often be obtained by placing the sitter quite in the open air, but when the Collodion and Bath are in the condition for giving great intensity of image, the gradation of tone will be inferior unless the light be prevented from falling too strongly upon the face and hands.

In focussing the object, cover the head and the back part of the Camera with a black cloth, and shift the Lens gently until the greatest possible amount of distinctness is obtained. Then insert the sensitive plate, and having raised the door of the slide, cover all with a black cloth during the exposure, as a security against white light finding entrance at any part excepting through the Lens.

With regard to the proper time for the exposure, so much depends upon the brightness of the light and the nature of the Collodion, that it must be left almost entirely to experience. The following general rules however may be of use:—

In a tolerably bright day in the spring or summer months, and with a newly-mixed Collodion, allow four seconds for a Positive Portrait, and eight seconds for a Negative. With a double-combination Lens of large aperture and short focus, perhaps three seconds, and six seconds, or even less, may be sufficient.

In the dull winter months, in the smoky atmosphere of large cities, or when using an old Collodion brown from free Iodine, multiply these numbers three or four times, which will be an approximation to the exposure required. It is by the appearance presented under the influence of the developer, which will immediately be described, that the operator ascertains the proper time for exposure to light.

THE DEVELOPMENT OF THE IMAGE.

The details of developing the latent image differ so much in the case of Positive and Negative pictures, that it is better to describe the two separately.

The development of direct Positives.—With Sulphate of Iron as a developer, it is most simple to develope the image by immersion. The solution may conveniently be poured into a vertical trough, such as that used for exciting, and the plate immersed by means of a glass dipper in the usual way. Unless the weather be cold, the image makes its appearance in three or four seconds, and the film is then immediately washed with clear water. Whilst in the Bath, the plate is kept in gentle motion, and the operator must not expect to see the image very distinctly, except the high lights; the shadows, being faint, are partially concealed by the unaltered Iodide, but they come out during the fixing. The action of the Sulphate of Iron is stopped at an early period, or an excess of development will be incurred. The Bath may be used repeatedly.

In using Pyrogallic Acid or Nitrate of Iron to develope glass Positives, the plate may be placed upon a levelling-stand, or held in the hand, or by the pneumatic holder, and the solution poured on quickly at one corner; by blowing gently or inclining the hand, as the case may be, it is scattered evenly over the film before the development commences.

If any difficulty is experienced in covering a plate evenly with a strong developer before the action commences, it may be overcome by using a shallow cell formed by cementing two or three thicknesses of window-glass on a piece of patent plate to the depth of a quarter of an inch. The size of the cell should be only slightly larger than the plate intended to be developed, that the waste of fluid may be as little as possible.

The cell is held in the left hand, and the plate being placed in it, a sufficient quantity of the developer is poured on at one corner. By a slight inclination, the fluid is caused to flow in a uniform sheet over the surface of the film, backwards and forwards. The image starts out quickly, and the developer is then at once poured off, and the film washed as before.

It is very important in developing Positives to use a sufficient quantity of the solution to cover the plate easily; otherwise oily stains and marks are formed, from the developer not combining properly with the surface of the film. For a plate five inches by four, three or four drachms will be required, and so in proportion for larger sizes.

The appearance of the Positive image after developing, as a guide to the proper time of exposure.—When the plate has been developed, it is washed, fixed, and laid upon a dark ground, such as a piece of black velvet, for inspection.

In the case of a portrait, if the features have an unnaturally black and gloomy appearance, the dark portions of the drapery, etc., being invisible, the picture has been under-exposed.

On the other hand, in an over-exposed plate, the face is usually pale and white, and the drapery misty and indistinct. Much however in this respect depends upon the dress of the sitter (see p. 66), and the manner in which the light is thrown; if the upper part of the figure is shaded too much, the face may perhaps be the last to be seen. The operator should accustom himself to expend pains in the preliminary focussing upon the ground glass, and to ascertain at that time that every part of the object is equally illuminated. For this reason, pictures taken in a room are seldom successful; the light falls entirely upon one side, and hence the shadows are dark and indistinct.

The development of Negative Pictures.—This process differs in most respects from that of Positives. In the latter case, there is a tendency to over-develope the image; but in the former, to stop the action at too early a period; hence it is common to find Negative Pictures which are insufficiently developed, and too pale to print well.

In developing Negatives, many operators place the plate upon a levelling-stand, and distribute the fluid by blowing gently upon the surface; others prefer holding it in the hand and pouring the fluid on and off from a glass measure. The quantity of developer required will be less than that used for Positives, inasmuch as, if the Acetic Acid be present in sufficient excess, it is easy to cover the plate before the action begins. Some Collodion however, especially the glutinous kind, seems to repel the developer and prevent it from running up to the edge of the plate. When this is the case, or when oiliness and stains are produced, from the Bath being old and containing Ether, Alcohol must be added to the solution of Pyrogallic Acid.

With ordinary Negative Collodion, an addition of Nitrate of Silver to the developer will often be required; but the Pyrogallic Acid is to be used alone until the image has reached its maximum of intensity, which it will do in a minute or so, according to the temperature of the developing room. The plate may then be examined leisurely by placing it in front of, and at some distance from, a sheet of white paper. If it is not sufficiently black, add about four drops of the Nitrate Bath to each drachm of developer, stir well with a glass rod, and continue the action until the requisite amount of intensity is obtained. When there is any disposition in the plate to fog towards the end of the development, it may be obviated by fixing with Cyanide of Potassium (not Hyposulphite), and then, after a careful washing, intensifying with Pyrogallic Acid and Nitrate of Silver in the usual way. The glass which contains the mixture of Pyrogallic Acid and Nitrate of Silver must be washed out after each plate, as the black deposit hastens the discoloration of the fresh solution (p. 179).

Appearance of the Negative image during and after the reducing process, as a guide to the exposure to light.—An under-exposed plate developes slowly. By continuing the action of the Pyrogallic Acid, the high lights become very black, but the shadows are invisible, nothing but the yellow Iodide being seen on those portions of the plate. After treatment with the Cyanide, the picture shows well as a Positive, but by transmitted light all the minor details are invisible; the image is black and white, without any half-tone.

An over-exposed Negative developes rapidly at first, but soon begins to blacken slightly at every part of the plate. After the fixing is completed, nothing can often be seen by reflected light but a uniform grey surface of metallic Silver, without any appearance (or, at most, an indistinct one) of an image. By transmitted light the plate may appear of a red or brown colour, and the image is faint and dull. The clear parts of the Negative being obscured by the fogging, and the half-shadows having acted so long as nearly to overtake the lights, there is a want of proper contrast; hence the over-exposed plate is the exact converse of the under-exposed, where the contrast between lights and shadows is too well marked, from the absence of intermediate tints.

A Negative which has received the proper amount of exposure, usually possesses the following characters after the development is completed:—The image is partially but not fully seen by reflected light. In the case of a portrait, any dark portions of drapery show well as a Positive, but the features of the sitter are scarcely to be discerned. The plate has a general aspect as of fogging about to commence, but not actually established. By transmitted light the figure is bright, and appears to stand out from the glass: the dark shadows are clear, without any misty deposit of metallic Silver; the high lights black almost to complete opacity. The colour of the image however varies much with the state of the Bath and Collodion and with the brightness of the light.

The remarks already made under the head of Positives, apply equally well to Negatives; that is, it will be difficult to secure gradation of tone, unless the object be equally illuminated, without any strong contrast of light and shade. Hence the direct rays of the sun are, as a rule, to be avoided, and curtains, etc., employed when practicable.

FIXING AND VARNISHING THE IMAGE.

After the development is completed, and the plate has been carefully washed by a stream of water, it may be brought out to the light and treated with the Hyposulphite or Cyanide, until the unaltered Iodide is entirely cleared off. Some use a Bath for the Cyanide; but it is doubtful whether much saving is effected by doing so. The plate is again to be carefully washed after the fixing; and especially if Hyposulphite of Soda be used. Three or four minutes in running water will not be too long, or the glass may be left in a dish of water for an hour or two. If such precautions are neglected, crystals form on drying, and the image is injured.

Collodion pictures should be protected by a coat of varnish, both Negatives and Positives having been known to fade when exposed to damp air without any covering (see p. 166). To prepare transparent varnish. Amber may be dissolved in Chloroform according to Dr. Diamond's formula;—about 80 grains of amber-beads or pipe-stems should be digested with one ounce of the Chloroform, and the clear portion separated by filtration. It may be poured on the plate in the same manner as Collodion, and dries up speedily into a hard and transparent layer. The Spirit Varnish ordinarily sold for Negatives requires the aid of heat to prevent the gum from chilling as it dries; the plate is first warmed gently and the varnish poured on and off in the usual way; it is then, whilst still dripping, held to the fire until the Spirit has evaporated. A few trials will render the operation easy to perform. White Lac dissolved in strong Alcohol or in Benzole has also been recommended for clear varnish.

Direct Positives are to be varnished, first with a layer of transparent varnish, and then with black japan. Suggett's patent jet is sometimes employed, but it has a disagreeable smell, and is apt to crack on drying. The best black japan used by coachmakers is more elastic and less liable to crack. Asphalt (4 oz.) dissolved in mineral Naphtha (10 oz.), with the addition of 30 grains of Caoutchouc dissolved in half an ounce of the same menstruum, is also said to stand well. A third formula contains black sealing-wax dissolved in Alcohol. In either case it will be best to apply first a layer of clear varnish to the film, and afterwards the black varnish, which should combine with the other without dissolving it.

Positives whitened with Bichloride of Mercury are injured by varnishing; they must therefore be backed up with black velvet, or Japan laid upon the opposite side of the glass. Many prefer taking the picture upon coloured glass, using only a layer of clear varnish; but in this case the Collodion side being left uppermost, the image is necessarily reversed.

SECTION II.

Directions for the use of Photographic Lenses.

Those who are comparatively unacquainted with the science of optics require simple rules to guide them in the choice of a photographic lens, and in the proper mode of using it.

Two kinds of Achromatic lenses are sold, the Portrait lens and the View lens; the former of which is constructed to admit a large volume of light, for the purpose of copying living objects, etc.

A convenient-sized Camera for small portraits is "the half-plate" with a lens of about 2¼ inches diameter, and giving a tolerably flat field on a surface of 5 inches by 4. Much however in this respect will depend upon the quality of the glass and also upon its focal length; a short focus lens taking a picture more quickly, but giving a smaller image, and a field which is misty towards the edge. There is also a great tendency to distortion of the image in portrait lenses of large aperture and short focus, such as those employed for operating in a dull light.

The "whole plate" portrait lens may be expected to cover 6½ by 4¾ inches, and has a diameter of about 3¼ inches. It will take larger pictures than the last, but not necessarily in a shorter time; since, although the aperture for admitting the light is larger, the focal length is proportionately greater and the light less condensed.

The "quarter-plate" portrait lens of 1¼ inch diameter is useful for stereoscopic subjects and small portraits; which are usually more sharply defined when taken with a small lens.

The distance at which the Camera is to be placed from the sitter in taking a portrait, will depend upon the focal length of the lens. The effect of bringing the Camera nearer is to add to the size of the image, but at the same time to increase the chance of distortion; hence with every lens of full aperture, there is a practical limit to the size of picture which can be taken.

When it is required to obtain a large image with a small lens, a stop with a central aperture (which may be readily made of a piece of circular cardboard blackened with Indian ink) must be placed in front of the lens. This will diminish the amount of light, but will render the picture more distinct towards the edge, and bring a variety of objects at different distances into focus at the same time. With a stop attached, the lens may also be brought nearer to the object without distorting.

With regard to this subject of the distortion often produced by lenses, observe particularly, that with the portrait combination of full aperture, and especially when the powers of the glass are rather strained by its being advanced too near to the sitter,—all objects near to the lens will be magnified, and those more removed will appear diminished; hence, as the position of the sitter is never quite vertical, the Camera must be inclined a little downwards, or the hands and feet will be enlarged, the figure in fact becoming pyramidal with the base below; whereas on the other hand, if the inclination of the Camera be too great, the head and forehead will be enlarged, and the figure becomes a pyramid with the base above.

When groups are taken, arrange the objects as near as possible equidistant from the lens, and use a stop if practicable. Long-focus lenses are the best for this purpose, allowing the Photograph to be taken further off, and giving a greater variety of objects in focus at the same time.

Portrait lenses may often be advantageously substituted for View lenses in copying objects of still life which are badly lighted. The aperture of the lens being large, a Negative can be obtained with an amount of light which would not suffice if a small stop were used. On the other hand, if the light be unusually bright, the lens of full aperture is always the most likely, from its extent of reflecting surface, to produce a misty and indistinct image. Hence the object should be well backed up with some neutral colour, or, if that cannot be done, a pasteboard funnel, projecting about a foot and a half, may be fastened in front of the lens, in order to exclude rays of light not immediately concerned in the formation of the image. If the lens were turned towards distant objects brightly illuminated, and a portion of sky included, there would probably be diffused light, and consequent fogging of the plate on the application of the developer. This effect will also invariably follow if the sun's rays be allowed to fall directly upon the glass.

Directions for finding the Plane at which the Sharpest Image can be obtained.—Non-Achromatic Lenses are understood by all to require correction for the chemical focus; but it is usually said of the compound glasses, that their two foci correspond. The amateur is recommended, in order to avoid disappointment, to test the accuracy of this statement, and also to see that his Camera is constructed with care. To do this, proceed as follows:—

First ascertain that the prepared sensitive plate falls precisely in the plane occupied by the ground glass. Suspend a newspaper or a small engraving at the distance of about three feet from the Camera, and focus the letters occupying the centre of the field; then insert the slide, with a square of ground glass substituted for the ordinary plate (the rough surface of the glass looking inwards), and observe if the letters are still distinct. In place of the ground glass, a transparent plate with a square of silver-paper which has been oiled or wetted, may be used, but the former is preferable.

If the result of this trial seems to show that the Camera is good, proceed to test the correctness of the Lens.—

Take a Positive Photograph with the full aperture of the portrait Lens, the central letters of the newspaper being carefully focussed as before. Then examine at what part of the plate the greatest amount of distinctness of outline is to be found. It will sometimes happen, that whereas the exact centre was focussed visually, the letters on a spot midway between the centre and edge are the sharpest in the Photograph. In that case the chemical focus is longer than the other, and by a distance equivalent to, but in the opposite direction of, the space which the ground glass has to be moved, in order to define those particular letters sharply to the eye.

When the chemical focus is the shorter of the two, the letters in the Photograph are indistinct at every portion of the plate; the experiment must therefore be repeated, the lens being shifted an eighth of an inch or less. Indeed it will be proper to take many Photographs at minute variations of focal distance before the capabilities of the lens will be fully shown.

The object of finding the point at which the sharpest image is obtained will also be assisted by placing several small figures in different planes and focussing those in the centre. This being done, if the more distant figures come out distinctly in the Photograph, the chemical focus is longer than the Visual, or vice vers when the nearest ones are most sharply defined.

The Single Achromatic Lens.—A useful lens for landscape Photography is one of about 3 inches diameter and 15 inches focal length, which may be expected to cover a field of 10 inches by 8. With the lens, stops are supplied of various diameters, the largest of which will be useful in dull weather; the smaller when the field is required to be rendered sharp to the very edge.

The stop is arranged at a certain distance in front of the lens, and must not be moved. If it were brought close up to the glass, the field would not be so flat; the effect being then the same as that of a stop placed in front of a Portrait Lens, viz. simply to cut off the outside portion of the glass.[38]

In taking Photographs of architectural and other subjects with vertical outlines, it is very important to have the Camera placed perfectly horizontal; since, if it be inclined either upwards or downwards, the perpendiculars will be destroyed and the object will appear of a pyramidal form, falling inwards or outwards, as before shown. It is convenient to rule the ground focussing glass with a number of parallel lines in both directions, which enables the operator at once to see that the position of the instrument is correct.

SECTION III.

Mode of copying Engravings, Etchings, etc.

The engraving to be Photographed should be removed from its frame (the glass causing irregular reflection) and suspended vertically and in a reversed position, in a good diffused light. A black cloth may be placed behind the picture with advantage if any surface likely to reflect light be presented to the lens.

The Camera must be fixed immovably, so as not to vibrate in the least degree when the cap of the lens is taken off. It should be pointed at right angles to the picture, and the focus determined in the ordinary way. Either a portrait or a single lens may be used, with a diaphragm sufficiently small to render the image distinct up to the edge.

It is not desirable to employ too thin a Collodion, since perfect opacity of the darkest parts of the Negative is essential. An old Collodion containing free Iodine is better than a contractile Collodion, as giving a more intense and clear image. Pure Collodion iodized with Iodide of Cadmium, if found wanting in intensity, may be at once rendered fit for use in copying engravings by adding Glycyrrhizine (p. 209), until the dark parts of the negative become very opaque, and subsequently softening the excessive hardness, if necessary, by dropping alcoholic solution of Iodine into the Collodion until it reaches a straw-yellow tint. A second formula useful in iodizing Collodion for a similar purpose is as follows.

This, with addition of Glycyrrhizine, will give a very black image.

Etchings, diagrams, and drawings with pencil or ink, without much middle-tint, if on thin paper, are easily copied without the aid of the Camera, by simply laying the sketch upon a sheet of Negative Paper, exposing for a brief time to the light, and developing with Gallic Acid. This yields a Negative which is employed for printing Positives in the usual way. Full directions on this subject will be found in the Second Section of the following Chapter.

A more simple plan, and one which will succeed when great delicacy is not required, consists in laying the sketch upon a sheet of Positive printing paper (a highly salted paper will be the best, as giving most intensity) and exposing to the light until a copy is obtained. All the details are faithfully rendered in this way, but it is sometimes difficult to obtain a Negative sufficiently black to yield a vigorous print.

SECTION IV.

Rules for taking Stereoscopic Photographs.

Binocular pictures of a large size, for the reflecting Stereoscope, may be taken with an ordinary View lens of about 15 inches focus. The ground glass of the Camera having been ruled with cross lines in the manner described at page 231, the position of some prominent object is marked upon one of the lines with a pencil, and the first view is taken. The stand is then moved laterally to the proper distance, and the Camera adjusted to its second position by shifting it until the marked object occupies the same place as before. The distance between the two positions should be about one foot when the foreground of the picture is twenty-five feet from the instrument, or four feet when it is at thirty or forty yards. But, as before shown at page 71, this rule is not to be followed implicitly, much depending upon the character of the picture and the effect desired.

Photographs for the lenticular Stereoscope are taken with small lenses of about 4½ inches focus. For portraits, a Camera may advantageously be fitted with two double-combination lenses, of 1¾ inches diameter, exactly equal in focal length and in rapidity of action. The caps are removed simultaneously, and the pictures impressed at the same instant. The centres of the lenses may be separated by three inches when the Camera is placed at about six feet from the sitter, or four inches when the distance is increased to eight feet.

Pictures taken with a binocular Camera of this kind, require to be mounted in a reversed position to that which they occupy on the glass: for since the image of the Camera is inverted, when it is turned round and made erect, the right-hand picture will necessarily stand on the left side, and vice versÂ.

Mr. Latimer Clark has devised an arrangement for taking stereoscopic pictures with a single Camera, which is exceedingly ingenious. Its most important feature is a contrivance for rapidly moving the Camera in a lateral direction without disturbing the position of the image upon the ground glass. This will be understood by a reference to the following woodcut.