Towler, John. The Silver Sunbeam. Joseph H. Ladd, New York: 1864. Electronic edition prepared from facsimile edition of Morgan and Morgan, Inc., Hastings-on-Hudson, New York. Second printing, Feb. 1974. ISBN 871000-005-9
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A COLLODION negative is an actinic impression, in which the different parts of the image are, as in the positives just described, laterally inverted, and, when viewed by transmitted light, the shades are where the lights ought to be, and vice versa. It is the matrix from which positives are obtained by direct contact, either on glass, or on paper, as also by means of the lens in the ordinary, or in the solar camera. Most of the details of the operation in the negative process are the same precisely as in the positive process.
The glass is filed, cleaned and flowed with collodion, as before directed. It is sensitized too in the same bath, and then exposed. Let the time of exposure be from ten to twenty seconds in the glass-room, probably more; much depends upon the proper adjustment of the light, and its concentration by the lenses. The object in view is to obtain much more actinic action, not only on the film, but through the film, so as to produce a denser metallic reduction for the shades, which in the ambrotype are lights. To guard against the liability to fogging, a much weaker and more acid developer is used than in the positive process. The developing is carried on as long as the shades increase in density by transmitted light. It is quite an advantage in this process to have a small square of orange-colored glass situated lower down than the position of the negative, as you hold it for the operation of development, in order that the light may come from below, and thus through the glass. If fogging sets in, or the density seems to be stationary, or even to retrograde, the negative is developed as far as circumstances in the present instance will permit. If the density of the shades is so great as to prevent you from distinguishing objects through them, and these shades are regularly tempered down through the intermediate tones to the bright lights, and these lights are still clear and transparent, it is very possible that the image is sufficiently negative, and that you have succeeded in your undertaking. It is absolutely necessary that you should know what you have to do, before you can depend upon what you do, or rely on definite results. A true negative is just what I have described. If the lights are not clear and transparent, with sufficient detail, of course, intermingled; if the shades are transparent, and not comparatively opaque, so much so as to allow the print of a book to be read through them; or if there are no intermediate tints, but your negative is all black and white; then you have not succeeded-your negative is faulty. We will suppose, however, that the three gradations of shades, middle tones, and lights exist, but that the intensity of the shades is not strong enough; there is a general weakness in the negative, and your object is to push on the development, which is found to be ineffectual without producing a haziness or fogginess over the whole print; the conclusion to be drawn from this circumstance is that the time of exposure was too short. Another sitting may remedy the evil. On the contrary, if when the developer is poured on, the reduction on the shades is very rapid, and this reduction commences, rushes with rapidity into the lights before you have time almost to stop it, you may fairly conclude that the time was too long. But a developer sometimes may produce very much the same effect; for, if the proportion of the iron salt, in comparison with the acid and the water, be great, fogging and rapid reduction will certainly be the result. As before remarked, a much weaker developer is required in the preparation of a negative than in that of a positive, and a proportionately larger quantity of acid to check its action, until the proper density of opacity is attained in the shades. (I use the words shades and lights in the negative, to represent what they really are, and not whit they produce on the paper print; shades are darn and opaque; lights are thin and transparent.)
We do not aim to obtain brilliant white silver reductions on the negative; for the color, or metallic brilliancy is altogether a matter of little consequence; on this account we use no silver solution in our negative developer. Where the time of exposure is not necessarily required to be very short, a pyrogallic acid developer produces a very pleasing negative.
Formula No. 1. Iron Developer.
|Sulphate of the protoxide of iron,||4 drachms.|
|Acetic acid,||1½ ounces.|
Formula No. 2. Pyrogallic Acid Developer.
|Pyrogallic acid,||3 grains.|
|Acetic acid,||2 drachms.|
The negatives which produce the softest prints are those which are produced by the first development, where the time of exposure and the action of the reducing agents have been in such relatively due proportion as to produce the three gradations with a proper amount of opacity in the shades. This proportion can not always be determined beforehand, because of the variability of the light, and its actinic powers, of which we know as yet absolutely so little. We can not determine the reason of the widely diverse action, of light at six in the morning, and six in the evening, or at the vernal equinox, and the autumnal. In consequence of this want of definite knowledge of the prime cause that institutes the actino-physical changes in the iodo-sensitized collodion film, it will frequently happen that the developed image is not perfect; the shades are not endowed with sufficient opacity. Fortunately in such cases we possess means whereby these shades, middle tones, and detail in the lights can all be in relative proportion rendered more opaque, and as much more opaque as may be desired. The process by which this end is attained, is denominated the Intensifying or Redeveloping process.
The image having been developed as far as possible in accordance with the rules laid down, the plate is thoroughly and carefully washed on both sides, and freed entirely from every trace of nitrate or developer. Cyanide of potassium in solution, the formula of which is given at the end of the positive process, may be employed to remove the undecomposed iodides or bromides, care being taken not to continue the action of the solvent too long, nor to apply it in too concentrated a condition, lest the fine markings of detail are dissolved off at the same time. Because, as already mentioned, cyanide of potassium is a reducing agent, as well as a fixing substance, and giving a silver salt so acted upon a reguline appearance, it is regarded as the fixing agent proper for collodion positives; whereas, owing to the properties possessed by hyposulphite of soda as a fixer alone, and not a reducer, and because its solvent action is not so violent as that of the cyanide, it is properly recommended to fix negative pictures.
Formula No. 1.
|Hyposulphite of soda,||5 ounces.|
Formula No. 2.
|Cyanide of potassium,||1 drachm.|
In case the image is fixed with the first formula, that is, with hyposulphite of soda, the plate requires to be washed with the utmost care, for if any of the hyposulphite of silver is left in the film, it will become manifest after the drying of the film, sometimes at the expiration of months, by the formation of a crop of crystals on the surface that completely ruins the picture. As soon as washed, the plate is ready for operations quite distinct from those in the positive process.
Formula No. 1. Depositing Fluid.
|Iodide of potassium,||1 grain.|
Formula No. 2. For the Stock Bottle of the same material.
|Iodide of potassium,||1 drachm.|
|Iodine to saturation.|
Take from ten to twenty drops of this solution to each ounce of water, and flow the developed plate with it. This operation can be performed in the diffused light of day. The plate mast be kept, in motion all the while, and the fluid poured off and on, in order to obviate all irregular deposition. The solution will gradually lose color, whilst the film in the mean time assumes a gray or yellowish-gray hue. If the negative does not require much additional opacity in the shadows, it is not necessary to carry on the depositing operation further than the gray film. The plate is now washed again.
Formula No. 1. Nitrate of Silver.
|Nitrate of silver,||30 grains.|
|Rain, or distilled water,||1 ounce.|
Take three drops of this solution with two drachms of water, and cover the plate with the fluid. Pour the fluid off and on several times.
Formula No. 2. Pyrogallic Acid. (Stock.)
|Pyrogallic acid,||12 grains.||Keep in a dark place.|
|Acetic acid,||1 ounce.|
Formula No. 3.
|Of this take,||1 drachm.||For immediate use.|
To two drachms of No. 3, add ten drops of No. 1; mix intimately by shaking, and then pour it upon the plate, and keep it in agitation. The shades will soon increase in blackness and opacity. The operation is carried on to the greatest advantage by holding the negative over a light reflected from below, as m the dark-room, or near a doorway receiving its light from the sky. Stand sufficiently far back, and sidewise of the door, so that the light does riot shine upon the negative directly from the sky, but is received as it is reflected upward from the floor, etc., below. The shadows will grow darker and darker; and the process has to be stopped as soon as the opacity is sufficiently dense. Experience alone can tell you exactly when to stop. The denser the background in the negative, if a white screen were used, the whiter the print will be; but the opacity may be so great as to require an hour or two for the subsequent printing operation, which is very inconveniently long. A certain connection exists, therefore, between the negative effect and the positive printing effect afterward, which experience has to teach; and even if you do not execute your own printing,, this connection must not be lost sight of. In pmts that must really appear white in the paper, the opacity mast be dense enough to prevent you from reading print through them; taking this for your guide, separate such a part in the picture; keep your eye steadfastly upon it as it increases in darkness, and when it has arrived at the point indicated, pour off the intensifying solution, and wash very thoroughly. It sometimes happens that the film becomes contracted by this operation, or that the fluid gets between the glass and the film, and thus the latter becomes loosened, and is liable to peel off. Careful experience will teach you how to retain the collodion in its place.
Where many prints have to be taken from a negative, it is quite requisite to varnish the film when dry. But almost all varnishes have a penetrating effect, like oil of turpentine on paper, and thus diminish the opacity of the negative. This has to be taken into consideration, aid the negative must be intensified in accordance deeper than required when without varnish. The property of a varnish, suitable for such purposes, must be a sufficient hardness of film to prevent scratches, insolubility by the heat of the sun, freedom L from any liability to cracking by contractility, perfect transparency, as little penetrating power as possible, and freedom from all action upon the film.
|White lac,||4 ounces.|
|Picked sandarac,||4 drachms.|
|Alcohol, (concentrated,)||60 ounces.|
|Oil of bergamot,||20 drops.|
Dissolve by the aid of a water-bath, and filter.
To obviate the diminution of opacity by means of the varnish, I frequently flow the plate with a dilute solution of gum-arabic or gelatine, which is allowed to dry; and then the plate is varnished.
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