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
|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.
|[Previous] Chapter 21||[Next] Chapter 23||Title Page|
|Table of Contents||Search this book||Albumen Home|
Home ~ Library ~ Science ~ Technology ~ Gallery ~ Video ~ Forum ~ About ~ Search