_To make Pyroxyline or Gun-cotton, suitable for Photographic Collodion._
1. By nitre process: Oil of vitriol (s. g. 1.70) 6 oz.; dried nitrate of potash, 3 1/2 oz.; water, 1 oz. Mix the acid and the water in a porcelain vessel, and add the pulverized nitre, gradually stirring with a glass rod until the lumps disappear and the mixture becomes transparent. Place a thermometer in the mixture, and when it indicates between 145 and 150 Fahr., the cotton should be immersed. Take 60 grs. of clean cotton, and separate it into 10 or 12 bolls, and immerse the bolls separately, and leaving the whole in the mixture for 10 minutes. Should the temperature fall to 140, float the cup on boiling water, and maintain it between 140 and 150. At the expiration of 10 minutes lift the cotton with glass rods, and squeeze out the acid quickly and dash the mass into a large vessel of clean, cold water, separating the mass so as to wash it thoroughly and quickly. Complete the washing by immersion for several hours in running water, then spread it out to dry spontaneously.
2. By mixed acids: Oil of vitriol (s.g. 1.845), 18 oz.; nitric acid (s. g. 1.457), 6 oz.; water, 5 oz. Mix the nitric acid and water in a porcelain vessel, then add the oil of vitriol and mix thoroughly and allow the mixture to cool to 150 Fahr., when immerse the cotton. Take 300 grs. of clean cotton, well loosened, and immerse piecemeal, so as to saturate thoroughly with the acids. Allow the whole to remain 7 minutes, after which time lift it out with the rods and wash it precisely as directed in last process.
Pure alcohol (s. g. 0.805), 10 oz.; pure ether (s. g. 0.725), 20 oz.; prepared cotton, 300 grs. Pour the alcohol into a 40 oz. glass bottle, add the cotton, and shake until the cotton is thoroughly wetted; then add the ether, shake well and set away in a cool, dark place for several weeks to settle. Mark "Plain Collodion." In very warm weather increase the proportion of alcohol by addition a day before use or at time of iodizing.
_Iodizers for Photographic Collodion._
Iodide of ammonium, 90 grs.; iodide of cadmium, 30 grs.; bromide of ammonium, 40 grs.; alcohol (8.10), 10 oz.
Or, iodide of magnesium, 200 grs.; bromide of cadmium, 50 grs.; alcohol (810), 10 oz.
Pulverize the salts, and add gradually to the alcohol, commencing with the bromide; shake until completely dissolved, and set away in a dark place. Mark "Iodizing Solution."
_To Iodize Collodion._
Plain collodion, 3 oz.; iodizing solution, 1 oz. Mix and set away in a dark, cool place 12 hours before using.
Any of the ordinary iodides or bromides can be substituted in the above formula.
For positives: Pure re-crystallized nitrate of silver (437 gr.), 1 oz.; pure nitric acid, 3 minims; alcohol, 2 drs; distilled water, 10 oz.; iodide of potassium, 1 gr. Dissolve the nitrate of silver in 3 oz. of the distilled water, add the iodide of potassium, shake and allow to settle; test for acidity with blue litmus paper, and, if present, neutralize carefully with a solution of carbonate of soda. When neutral, add the remaining 7 oz. of distilled water, filter and add the alcohol and nitric acid, and the bath is ready for use.
For negatives: Pure recrystallized nitrate of silver, 1 oz.; glacial acetic acid, 5 minims; alcohol, 3 drs.; iodide of potassium, 1 gr.; distilled water, 10 oz. Dissolve the silver in 8 oz., and treat precisely as for bath for negatives, observing that it is to be acidified with glacial acetic acid in place of nitric acid.
These baths should be kept in a dark place, and always show an acid test. When out of order, boil for a few minutes, add one-tenth volume of distilled water and restore to the original strength by adding strong solution of crystallized nitrate of silver in distilled water, and acidifying with the proper acids.
For positives: 1. Pure sulphate of iron, 150 grs.; glacial acetic acid, 6 fl. drs.; water, 10 oz.; nitric acid, 2 minims. Dissolve the sulphate of iron in the water, and add the acetic and nitric acid and cork tightly.
2. Sulphate of iron, 480 grs.; nitrate of baryta, 320 grs.; alcohol, 1 oz.; nitric acid, 30 minims; water, 10 oz. Powder the nitrate of baryta and dissolve in the water warmed; when dissolved, add the powdered sulphate of iron stirring for a few minutes, filter, and when the liquid becomes cold, add the nitric acid and alcohol separately. Bottle and cork tightly
For negatives: 1. Pyrogallic acid, 10 grs.; glacial acetic acid, 3 drs.; distilled water, 10 oz. Dissolve the pyrogallic acid in the water, add the glacial acetic acid, cork tightly.
2. Sulphate of iron and ammonium, 2 oz., or sulphate of iron, 1 1/2 oz.; glacial acetic acid, 1/2 oz., or acetic acid No. 8, 1 1/2 oz.; alcohol, 1/2 oz.; distilled water, 10 oz. Add to the distilled water in the order indicated, the iron-salt to be first dissolved. In warm weather this developer requires dilution, and must be washed from the plate the instant the details appear.
For positives: Cyanide of potassium, 120 grs.; nitrate of silver, 6 grs.; water, 10 oz. When this solution requires more than a minute or two to clear the picture, add a small amount of cyanide of potassium.
[This solution is highly poisonous, and should not be allowed to touch unsound skin, nor should the fumes be breathed.
]For negatives: The above solution of cyanide of potassium answers very well, or hyposulphite of soda, 10 oz.; water, 10 oz.; ether, 30 minims.
_Strengthening or Intensifying Solutions_
Should be employed after the picture has been developed, fixed and carefully washed:
Nitrate of silver, 200 grs.; distilled water, 10 ounces.
Or, Bi-chloride of mercury, 30 grs.; distilled water, 40 oz.
_Cleaning the Glass Plates._
Before washing the glasses, each square should be roughened on the edges and at the corners by means of a file, whetstone, or a sheet of emery paper; or more simply by drawing the edges of two plates across each other.
A cream of Tripoli powder and spirits of wine with a little ammonia added, is commonly employed. A tuft of cotton is to be dipped in this mixture and the glasses well rubbed with it for a few minutes.
After wiping the glass carefully, complete the process by polishing with an old silk handkerchief, avoiding contact with the skin of the hand. Leather may be used instead of silk for the final polishing; they must be first beaten, then washed in pure water, dried in the sun and well pulled out until they are soft and yielding. Before deciding that the glass is clean, hold it in an angular position and breathe upon it.
Other modes of cleaning glasses have been recommended, of which, perhaps, the residues of collodion are the most simple. Add a fluidrachm of water to the ounce of collodion until the pyroxyline begins to form a white deposit not redissolved on agitation: this will prevent the collodion from evaporating too quickly. Then pour a little upon the glass and rub with a tuft of wool or piece of cambric. Clean off with a second piece, and finish with cloth and leathers as before, no water will be required.
New glass plates are frequently dotted on the surface with little gritty particles, which consist of carbonate of lime. They are not removed by potash or any alkali, but dissolve readily in a diluted acid, such as oil of vitriol, with about four parts of water added, or dilute nitric acid.
_Lea's Cleaning Solution._
Water, 1 pt.; sulphuric acid, 1/2 oz.; bichromate potash, 1/2 oz. The glass plates, varnished or otherwise, are left, say 10 or 12 hours or as much longer as desired, in this solution, and then rinsed in clean water and wiped or rubbed dry with soft white paper. It removes nitrate of silver stains from the fingers.
_Coating the Plate._
When the collodion is properly cleared from sediment, take a glass plate, previously cleaned, and wipe it gently with a broad camel's-hair brush in order to remove any particles of dust which may have subsequently collected. If it be a plate of moderate size it may be held by the corners in a horizontal position, between the forefinger and thumb of the left hand. The collodion is to be poured on steadily until a circular pool is formed extending nearly to the edges of the glass,
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 passes 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 next to be held 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 give a rocking movement, which makes the diagonal lines coalesce and produces 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.
With regard to the time which ought to elapse between coating and dipping, observe the following: After exposing a layer of collidion 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. This is termed setting, and when it takes place the time has come for submitting the plate to the action of the bath.
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 and let it remain until the oily appearance on the surface disappears.
After the plate has been taken out of the bath it should be exposed and developed with all convenient despatch, otherwise the film will become partially dry, the developing solutions will not flow easily, and the negative will be weak and metallic.
The pyrogallic acid solution having been previously measured out (about 3 drs. for a stereoscopic plate or a plate 5 X 4, 1 oz. for a 9 X 7, and 12 drs. for a plate l0 X 8), hold the glass in the band in the same manner as when coating it with collodion, and flow the liquid on evenly.
_Development with Sulphate of Iron._
This reducing agent developes the picture so rapidly, when the collodion contains only iodide, that its employment requires care. The solution should be thrown on to the plate rather quickly and with a sweep. In the course of a few seconds the image appears in all its parts, and the liquid on the film shows signs of commencing turbidity. When this happens, the developer must be poured off immediately, and the plate washed with water, otherwise the shadows will be misty from adherent particles of silver. Plates developed with sulphate of iron may be further blackened by washing the film and pouring over it a 20 gr. solution of nitrate of silver, followed by a second application of sulphate of iron. A better process, however, is to wash away all traces of the iron salt by a stream of water applied for a few seconds, and then to mix the ordinary solution of pyrogallic acid with nitrate of silver.
_Fixing and Varnishing the Negative._
Wash the film gently with water, and pour the solution of hyposulphite on and off until the whole of the iodide has been cleared away. The solution of hyposulphite becomes nearly black after a time, but this is of no importance, some operators considering that even a preliminary washing to remove the pyrogallic acid solution is unnecessary. A thorough washing after the hyposulphite will be essential. After the negative has been washed flow it over with a solution of gum Arabic, stand it on clean blotting-paper to dry; otherwise dust will ascend the film by capillary action, and give an appearance as if impurities had drained down from above. It is important that the plate should be dried by artificial heat before varnishing, and the negative will also look more neat if a damp cloth be first run along the edge with the finger and thumb, so as to scrape away the collodion, and leave a clear margin of 1/8 to 1/4 of an inch all round. After doing so remove with the nail or a camel's-hair brush any loose or detached particles of collodion, which otherwise might be washed on to the image by the varnish, and produce a spot.
_To Adjust Camera for Chemical Focus._
Take a photograph of a printed sheet with the full aperture of the portrait lens, the central letters 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 through which the lens has to be moved, in order to define those particulars sharply to the eye.
_Direct Positives on Glass._
In developing a glass positive, the solution of sulphate of iron should be flowed evenly over the film, and in some quantity, so as to wash off a portion of nitrate of silver into the sink.
_Pyrogallic Acid Developer._
Forty grs. of pyrogallic acid being dissolved in 1 oz. of glacial acetic acid, and 20 minims added to 1 oz. of water when required for use. The strong solution becomes black from decomposition in the course of a few weeks, but when diluted it has only a faint yellow tint, and is tolerably effective in bringing out the image. In place of acetic acid strong alcohol may be used as a solvent, 1/2 a dr. of pyrogallic acid being dissolved in 1 oz. of spirit, and 20 minims of the resulting liquid added to each oz. of acidified water. No attempt must be made, however, to combine acetic acid and spirit in one solution, since abundance of acetic ether would be generated by so doing. These plans of preparing a concentrated developer are useful for a few weeks' keeping, but are not recommended for an unlimited time
_To Copy Engravings._
To photograph a full-sized steel engraving on a plate not larger than 7X6 or 5X4, is a very simple operation, and no special directions will be needed. Remove the engraving from its frame (the glass would cause irregular reflection), and suspend it vertically and in a reversed condition, in a good diffused light, placing a black cloth behind it, if any bright reflecting surface be presented to the lens. Point at it a camera mounted with a portrait-lens, and if the image upon the ground glass appears misty towards the edge, make a diaphragm, and place it in front of the anterior glass. Instead of a portrait-lens an ordinary view-lens may be used, and as the field to be covered is small, a comparatively large diaphragm will suffice.
Be careful not to over-expose the plate, develop with pyrogallic acid, and fix with hyposulphite.
The additional deposit obtained, as above described, will often be found sufficient, and when such is the case the method is to be preferred, because the half-tones of a photograph are easily obliterated by too much intensifying. In the case of large copies of maps taken with orthoscopic lenses of long focus, the iodine method proves insufficient, and the fine lines of the drawing become partly obliterated during the prolonged development. In such a case it is advised to develop the plate only partially in the first instance, and to fix it with cyanide of potassium; then to intensify twice with pyrogallic acid, citric acid, and nitrate of silver, and lastly to treat the plate with the two following liquids: No 1. Iodine, 6 grs.; iodide of potassium, 12 grs,; water, 6 oz. No. 2. Sulphide of potassium, 1 dr.; water, 6 oz.
Apply No. 1, either in the yellow room, or in the daylight, until the whole of the image is converted into iodide of silver, and the deposit appears yellow throughout. Then pour water on the image from a jug, and apply No. 2, which must be allowed to remain until the yellow color changes to a deep reddish-brown. Lastly, dry the plate, and varnish in the usual way.
Photographs for the refracting stereoscope are taken with small lenses of about 4 1/2 inches focus. For portraits a camera may advantageously be fitted with two double-combination lenses of 1 3/4 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 3 inches, when the camera is placed at about 6 or 8 feet from the sitter. Pictures taken with binocular camera of this kind require to be mounted in a reversed position to that which they occupy on the glass, or a pseudoscopic effect will be produced. The negatives may be cut in half, the right half being printed on the left side, or the finished prints may be removed before mounting.
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