CLASSIFICATION OF CAUSES OF FAILURE IN THE COLLODION PROCESS.

SECTION I.

Imperfections in Negative and Positive Collodion Photographs.

The following may be mentioned:—fogging—spots— markings, etc.

CAUSES OF FOGGING OF COLLODION PLATES.

1. Over-exposure of the Plate.—This is likely to happen when using the full aperture of a double combination lens for distant objects brightly illuminated, the Collodion being highly sensitive. Also from the film being very blue and transparent, with too little Iodide of Silver (p. 114).

2. Diffused Light.—a. In the developing room. This is a frequent cause of fogging, and especially so when the common yellow calico is employed, which is apt to fade. Use a treble thickness, or procure the waterproof material, in which the pores are stopped with gutta-percha.—b. In the Camera. The slide may not fit accurately, or the door does not shut close. Throw a black cloth over the Camera during the exposure of the plate.—c. From direct rays of the sun or the light of the sky falling upon the lens. With the full aperture of a double combination Lens, a portion of sky included in the field (as for instance to form the background of a portrait) is apt to cause fogging. The portrait will probably be more brilliant if a funnel-shaped canvas bag, or a curtain with an oblong aperture admitting only the rays proceeding from the sitter, be placed in front of the Camera.

3. Alkalinity of the Bath.—This condition, explained at page 88, may be due to one of the following causes:—a. The use of Nitrate of Silver which has been too strongly fused (p. 13).—b. Constant employment of a Collodion containing free Ammonia or Carbonate of Ammonia (p. 89).—c. Addition of Potash, Ammonia, or Carbonate of Soda to the Nitrate Bath, in order to remove free Nitric Acid (p. 89).—d. Use of rain-water or hard water for making the Nitrate Bath (rain-water usually contains traces of Ammonia; hard water often abounds with Carbonate of Lime).

In either case the alkalinity may easily be removed by the addition of Acetic Acid, one drop to four ounces of the solution. The proper mode of testing for alkalinity is described at p. 89.

4. Decomposition of the Nitrate Bath.—a. By constant exposure to light (the injurious effects of this will be mostly seen when Positives are taken).—b. By organic matter: this is sometimes present in Nitrate of Silver which has been prepared from the residues of old Baths; or it may be introduced by floating papers for the printing process upon the Bath, or by dissolving the crystals of Nitrate of Silver in putrid rain-water, or in impure distilled water collected from the condensed water of steam-boilers and contaminated with oily matter.—c. Decomposition of the Bath by contact with metallic iron or copper, or with a fixing agent, or a developing agent (p. 90).

5. Faults of the developing solution.—a. Brown and decomposed solution of Pyrogallic Acid; this may sometimes be used with impunity, but it tends, as a rule, to facilitate irregular reduction of Silver.—h. Impure Acetic Acid having a smell of Garlic and which probably contains Sulphur in organic combination.—c. Omission of the Acetic Acid in the developer: this will produce a universal blackness.

6. Sundry other causes of fogging.—a. Vapour of Ammonia or Hydrosulphate of Ammonia, or the products of the combustion of coal-gas, escaping into the developing room.—b. Development of the image by immersion in solution of Sulphate of Iron: this is a safe plan when the films are formed in an acid Nitrate Bath; but with pale films formed in a chemically neutral Bath it is better to pour the fluid over the plate, and not to use the same portion twice.—c. Redipping the plate in the Bath before development: this is apt to give a foggy picture when using an old Bath, and is not recommended.

Systematic plan of proceeding to detect the cause of the fogging.—If the amateur has had but little experience in the Collodion process, and is using Collodion of moderate sensitiveness and a new Bath, the probability is that the fogging is caused by over-exposure. Having obviated this, proceed to test the Bath; if it is made from pure materials, and does not restore the blue colour of a piece of litmus-paper previously reddened by holding it over the mouth of a glacial Acetic Acid bottle, it may be considered in working order.

Next prepare a sensitive plate, and after draining it for two or three minutes in a dark place, pour on the developer: wash, fix, and bring out to the light; if any mistiness is perceptible, either the developing room is not sufficiently dark, or the Bath was prepared with a bad sample of Nitrate of Silver, or with impure Alcohol, or impure water.

On the other hand, if the plate remains absolutely clear under these circumstances, the cause of error may be in the Camera;—therefore prepare another sensitive film, place it in the Camera, and proceed exactly as if taking a picture, with the exception of not removing the brass cap of the lens: allow to remain for two or three minutes, and then remove and develope as usual.

If no indication of the cause of the fogging is obtained in either of these ways, there is every reason to suppose that it is due to diffused Light gaining entrance through the lens. This cause of error may often be detected by looking into the Camera from the front, when an irregular reflection will be seen upon the glass.

SPOTS UPON COLLODION PLATES.

Spots are of two kinds: spots of opacity, which appear black by transmitted light, and white by reflected light; and spots of transparency, the reverse of the others, being white when seen upon Negatives, and black on Positives.

Opaque Spots are referable to an excess of development at the point where the spot is seen; they may be caused by—

1. The use of Collodion holding small particles in suspension.—Each particle becomes a centre of chemical action, and produces a speck, or a speck with a tail to it. The Collodion should be placed aside to settle for several hours, after which the upper portion may be poured off.

2. Turbidity of the Nitrate solution.—a. From flakes of Iodide of Silver having fallen away into the solution, by use of an over-iodized Collodion.—b. From a deposit formed by degrees upon the sides of the gutta-percha trough.—c. From the inside of the trough being dusty at the time of pouring in the solution.

In order to obviate these inconveniences, it is well to make at least half as much again of the Nitrate solution as is necessary, and to keep it in a stock-bottle, from which the upper part may be poured off when required. The frequent filtration of Silver Baths is unadvisable, since the paper employed may be contaminated with impurities.

3. Dust upon the surface of the glass at the time of pouring on the Collodion.—Perfectly clean glasses, if set aside for a few minutes, acquire small particles of dust; each plate should therefore be gently wiped with a silk handkerchief immediately before being used.

4. Faults of the Slide.—Sometimes a small hole exists, which admits a pencil of light, and produces a spot, known by its being always in the same part of the plate; occasionally the door works too tightly so that small particles of wood, etc., are scraped off, and projected against the plate when it is raised. Or perhaps the operator, after the exposure is finished, shuts down the door with a jerk, and so causes a splash in the liquid which has drained down and accumulated in the groove below; this cause, although not a common one, may sometimes occur.

5. Insoluble particles in the Pyrogallic Acid.—The solution of Pyrogallic Acid will not usually require filtering, but if specks of Metagallic Acid are present, the developer should be passed through blotting paper before use.

Spots of Transparency may generally be traced to some cause which renders the Iodide of Silver insensible to light at particular points, so that on the application of the developer no reduction takes place.

1. Concentration of the Nitrate of Silver on the surface of the film by evaporation.—When the film becomes too dry after removal from the Bath, the solvent power of the Nitrate increases so much that it eats away the Iodide and produces spots.

2. Small particles of undissolved Iodide of Potassium in the Collodion.—These are likely to occur when Anhydrous Ether and Alcohol are employed. They produce transparent specks at every part of the plate. Allow the Collodion to settle, or add a drop of water, which will dissolve the Iodide.

3. Alcohol or Ether containing too much water.—This causes a reticulated appearance of the film, which is rotten and full of holes.

4. Use of glasses improperly cleaned.—This cause is perhaps the most frequent of all, when the film of Pyroxyline is very thin and the Bath neutral. After glasses have been long used it is often difficult to clean them so thoroughly that the breath lies smoothly; but the use of Potash gives the best chance.

MARKINGS OF VARIOUS KINDS ON COLLODION PLATES.

1. A reticulated appearance on the film after developing.—When this is universal, it often depends upon the employment of Collodion containing water. Or, if not due to this cause, the plate may have been immersed too quickly in the Bath, and the soluble Pyroxyline partially precipitated.

2. Oily spots or lines.—a. From raising the plate out of the Nitrate Bath before it has been immersed sufficiently long to have become thoroughly wetted.—b. Removal of the plate from the Bath before the Ether upon the surface has been washed away.—c. Redipping the plate in the Nitrate Bath after exposure to light, and pouring on the developer immediately; if a few minutes be not allowed to drain off the excess of Nitrate, the Pyrogallic Acid will not amalgamate readily with the surface of the film.—d. From the Nitrate Bath being covered with an oily scum, which is carried down by the plate. Draw a slip of blotting-paper gently along the surface of the liquid before using it.

3. Straight lines traversing the film horizontally.—From a check having been made in immersing the plate in the Bath.

4. Curved lines of over-development.—By employing the developer too concentrated; or by not pouring it on sufficiently quickly to cover the surface before the action begins; or by using too little Acetic Acid, and omitting the Alcohol. The addition of Alcohol to the developer will not be required as a rule when the Bath is newly made; but when much Ether has accumulated in it, the developer has a tendency to run into oily lines, unless containing Alcohol.

5. Stains from too small a quantity of fluid having been employed to develope the image.—In this case, the whole plate not being thoroughly covered during the development, the action does not always proceed with regularity.

6. Irregular striÆ.—From fragments of dried Collodion accumulating in the neck of the bottle, and being washed on the film; to avoid this, the finger should be passed gently round the inside of the neck before use.

7. Markings like those represented in the woodcut.—They are caused by using an inferior sample of Pyroxyline made from too hot acids, and are most seen when using an old Bath.

8. Stains on the upper part of the plate, from using a dirty slide.—To avoid these, place, if necessary, strips of blotting-paper between the supports and the glass.

9. Wavy marks at the lower parts of the plate.—a. If the Collodion is becoming thick and glutinous from constant use, dilute it with a little Ether containing an eighth part of Alcohol.—b. From reversing the direction of the plate after its removal from the Bath, so that the Nitrate of Silver flows back again over the surface and causes a stain on the application of Pyrogallic Acid.—c. Impurities on the woodwork of the frame ascending the film by capillary attraction. This is a frequent source of stains.

10. Marks from the developer not running up to the edge of the film (p. 212). Remedy this as far as possible by allowing the Collodion to set a little more firmly before dipping the plate in the Bath.

IMPERFECTIONS IN COLLODION NEGATIVES.

1. A want of Intensity.—a. From the development not having been sufficiently pushed (p. 224).—b. From the Collodion film being too blue and transparent for Negatives.—c. The Collodion newly made from pure materials (p. 114).—d. The plate kept too long between exciting and development (p. 100).—e. The Bath newly prepared from commercial crystallized Nitrate of Silver (p. 101).—f. The light too feeble, as on very dark wintry days, or in copying interiors, etc.

2. Inferior half-tones, with great intensity of the high Lights.—a. From the plate being insufficiently exposed.—b. The Collodion of inferior quality, either too strongly tinted with Iodine or made from impure materials.—c. The Nitrate Bath old and partially decomposed.—d. The light reflected too strongly from the object. When the light is unusually bright, a feeble Collodion and a newly mixed Nitrate Bath will be found to give better definition in the high lights than an intense Collodion, which may produce chalky Negatives.

3. The image pale and misty.—The plate is over-exposed (if so, the image will probably be a reddish-brown colour by transmitted light), or there is diffused light in the Camera or developing room. The presence of Bromides or Chlorides in the Collodion may occasionally produce the same effect.

4. The high lights of the image are solarized.—A change of colour to a light brown or red tint by transmitted light, with a dark shade by reflected light, is favoured by over-exposure of the plate, by organic decomposition of the Collodion, and by Acetate of Silver and other organic bodies in the Bath.

5. The image dissolves off on applying the Cyanide of Potassium.—The Collodion is probably over-iodized. The same thing may also happen in the Honey preservative process, when the plates have been long kept and the indurated layer of syrup not properly removed before applying the developer.

6. The developer does not run up to the edge of the film.—This is likely to occur when using Collodion nearly anhydrous; and particularly so with a new Bath not containing much Alcohol. The film will be less repellent, if a longer time be allowed before dipping in the Bath.

7. The film does not stick to the glass.—Clean the plates very carefully, and make the Collodion a little thinner if required. Allow a longer time before dipping in the Bath. A very effectual plan is to roughen the surface of the plates, about an eighth of an inch round the edges.

IMPERFECTIONS IN COLLODION POSITIVES.

The principal difficulty in the production of Negatives is to ascertain the right time of exposure to light and the proper point to which to carry the development of the image. A minor amount of fogging, stains, etc., is of less consequence, and will scarcely be noticed in the printing.

With direct Positives however the case is different. The beauty of these pictures depends entirely upon their being clean and brilliant, without fogging, specks, or imperfections of any kind. On the other hand, the exposure and development of Positives is comparatively simple and easily ascertained.

1. The shadows dark and heavy.—The plate has not received sufficient exposure in the Camera;—or the film being very transparent and the Silver solution weak, Nitric Acid is present in the Bath, or the Collodion is brown from free Iodine; in the latter case make the Collodion a little thicker, and develope with Sulphate of Iron in preference to Pyrogallic Acid.

2. The shadows good, but the lights overdone.—The developing fluid may have been kept on too long; or the object is not properly illuminated (p. 220); or the Collodion is not adapted for Positives.

3. The high lights pale and flat, the shadows misty.—The plate is over-exposed. Indistinctness of outline caused by over-exposure is distinguished from that produced by fogging by holding the plate up to the light; in the former case the image shows as a Negative.

If the Collodion is colourless, clearer shadows will probably be obtained by dropping in Tincture of Iodine until a yellow colour is produced.

4. The picture developes slowly; spangles of metallic Silver are formed.—Too much Nitric Acid is present in proportion to the strength of the Bath, to the amount of Iodide in the film, and to the quantity of Protosalt of Iron in the developer (p. 112).

5. Circular spots of a black colour after hacking up with the varnish.—These are often caused by lifting the plate too quickly out of the Bath; or by pouring on the developer at one spot, so as to wash away the Nitrate of Silver; or by the use of glasses imperfectly cleaned.

6. The image becomes metallic on drying.—If Sulphate of Iron is employed, the solution is too weak, or free Nitric Acid has been added in excess. If Pyrogallic Acid is used to develope, the proportion of Nitric Acid is too great.

7. A green or blue tint in certain parts of the image.—This is caused by the deposit of Silver being too scanty, which may happen from over-action of the light, or from the film of Pyroxyline being very thin;—if the Collodion is diluted down beyond a certain point, the same quantity of free Nitrate of Silver is not retained upon the surface of the film. Add a few drops of the Bath to the developer before pouring it on the plate.

8. Vertical lines, and mistiness, on the image.—If the Bath has been much used, add to it a third part of a simple solution of Nitrate of Silver in water, without any Alcohol or Iodide. Also prepare the developer with addition of Alcohol, to make it flow more readily (p. 211).

SECTION II.

Imperfections in Paper Positives.

1. The Print marbled and spotty.—The quality of the paper is often inferior, which causes it to imbibe liquids unevenly at different points; or the amount of Silver in the Nitrate Bath is insufficient. In this case the spots are often absent at the lower and most depending part of the sheet, where the excess of liquid drains off.

2. The Print clean on the surface, but spotted when held up to the light.—In this case the spots are probably due to imperfect fixation (see p. 129).

3. The Print becomes pale in the Hyposulphite Bath, and has a cold and faded appearance when finished.—The Chloride of Silver in the paper may have been in excess with regard to the free Nitrate of Silver; which is especially likely if no bronzing could be obtained by prolonged action of the light, or if a weak solution of Nitrate of Silver was laid on with a brush, or by a glass rod. Prints formed on paper which has been kept too long after sensitizing present the same appearance, the free Nitrate of Silver having entered into combination with the organic matter.

4. Yellowness of the light parts of the proof.—The following causes are likely to produce yellowness:—acidity of the fixing and toning Bath (p. 139),—its action continued for too long a time,—the first washings of the proof not performed quickly,—the toning Bath laid aside until it had become decomposed and nearly useless,—the paper kept for several days after sensitizing.

A creamy yellowness is also common in Prints toned by Sel d'or, when the Hydrochloric Acid has been omitted from the formula; the proof exposed to light during the toning and fixing process; or too long a time allowed to elapse between the toning and fixing. It is also more frequently met with on albuminized paper.

5. Intense bronzing of the deep shadows.—In this case the Negative is in fault; remedy the evil as far as possible by printing on paper containing but little salt.

6. The definition of the Print imperfect, the Negative being a good one.—Much will depend upon the quality of the paper. Towgood's Positive gives good definition. The use of Albumen will be a great advantage. Citrate of Soda (p. 246) will also improve the definition on plain paper.

7. Markings of a yellow tint in the dark portions of the Positive.—These are common on Prints toned without Gold; care should be taken not to handle the paper too much, either before or after sensitizing; to wash the prints in a clean vessel; and not to lay them down whilst wet on a wooden table or in contact with anything likely to communicate impurities.

8. Small specks and spots of different hinds.—These, when not corresponding to similar marks upon the Negative, are usually due to metallic specks in the paper; or to insoluble particles floating in the bath.

9. Markings of the brush in Ammonio-Nitrate pictures.—In this case there is probably an excess of Ammonia, which dissolves the Chloride of Silver. Add a little fresh Nitrate of Silver, or use the Oxide of Silver dissolved in Nitrate of Ammonia (p. 249).

10. Marbled stains on the surface of the Print.—Draw a strip of blotting-paper gently over the surface of the Nitrate Bath before sensitizing the paper; and see that the sheet does not touch the bottom of the dish.

11. Streaks on Albuminized paper.—Apply the Albumen more rapidly and evenly to the paper. If this does not succeed, add a little Ox-Gall (p. 243).

12. Removal of the Albumen from the paper during sensitizing.—The Nitrate Bath is probably alkaline (see page 89).