[49]The formula atp. 246may be modified with advantage: use double the quantity of Gelatine, and half the amount of Citrate and Chloride.
[49]The formula atp. 246may be modified with advantage: use double the quantity of Gelatine, and half the amount of Citrate and Chloride.
The Bath of Aceto-Nitrate is prepared as follows:—
Float the papers (Papier Saxe or Papier Rive) upon the Bath for three minutes, and suspend them to dry in a room from which actinic rays areperfectlyexcluded.
The exposure to light,—which is conducted in the ordinary printing frame, the Negative and sensitive paper being laid in contact in the usual way,—will seldom be longer than three or four minutes, even upon a dull day. It may be regulated by the colour assumed by the projecting margin of the paper; but it is quite possible to tell by the appearance of the image when it has received a sufficient amount of exposure:—the whole of the picture should be seen,excepting thelightest shades, and it will be found that very few details can be brought out in the development which were altogether invisible before the Gallic Acid was applied.
The developing solution is prepared as follows:—
In very cold weather it may be necessary to employ a saturated solution of Gallic Acid, containing about four grains to the ounce; whereas in warm weather the image will develope too quickly, and Acetic Acid must be added (see the remarks at the end of the process,p. 266).
To facilitate the solution of the Gallic Acid, stand the bottle in a warm place near the fire. A lump of Camphor floated in the liquid, or a drop of Oil of Cloves added, will to a great extent prevent it from becoming mouldy by keeping; but if once mould has formed, the bottle must be well cleansed with Nitric Acid, or the decomposition of the fresh Gallic Acid will be hastened.
Pour the solution of Gallic Acid into a flat dish, and immerse the Prints two or three at a time, moving them about, and using a glass rod to remove air-bubbles. The development is rapid, and will be completed in three or four minutes. If the Print developes slowly, becomesvery dark in colourby continuing the action of the Gallic Acid, but shows no half-tones, it has not been exposed sufficiently long to the light. An over-exposed proof, on the other hand, developes with unusual rapidity, and it is necessary to remove it speedily from the Bath in order to preserve the clearness of the white parts; when taken out to the light, it appears pale and red, with no depth of shadow.
The extent to which the development should be carried depends upon the kind of Print desired. By pushing the action of the Gallic Acid, a dark picture not much altered by the fixing Bath will be produced. But a better result as regards colour and gradation of tone will be obtainedby removing the Print from the developing solution whilst in the light red stage, and toning it subsequently by means of Gold; in which case it will correspond both in appearance and properties to a Positive obtained by the direct action of light (see the remarks atpage 167).
When it is intended to follow the latter plan, the action of the developer must be stopped at a point when the proof appears lighter than it is to remain; since the Sel d'or Bath adds a little to the intensity, and the image becomes somewhat more vigorous on drying.
Wash the Prints in cold water in order to extract all the Gallic Acid. Then tone withSel d'orin the manner described in the next Section, and fix in the usual way. The whites will with care be kept pure; or with only a faint yellow tinge, which is not objectionable.
Upon comparing the developed Prints with others obtained by the direct action of light upon the same sensitive paper, it is evident that the advantage isslightlyon the side of the latter; but the difference is so small that it would be overlooked in printing large subjects, for which the Negative Process is more especially adapted. Thecolourof both kinds of Positives is the same, or perhaps a shade darker in the developed proofs, which are usually of a violet-purple tone, but sometimes of a dark chocolate-brown.
A developing process with Serum of Milk.—The use of "whey" as a vehicle for Chloride of Silver has something the same effect as that produced by adding a Citrate. This may be traced to the presence of the Milk Sugar and of a portion of uncoagulated Caseine left in the Serum.
The only difficulty in the process is to coagulate the milk in such a way as to separate the greater part but not the whole of the Caseine. Milk which has become sour, or to which an acid has been added, is not considered so good for the purpose as that which has been treated with rennet; and even when rennet is used it must be of the best quality or its action will be imperfect. The serummust filter clear through, blotting-paper; but it should not run very rapidly, or in all probability the whole of the Caseine has been separated, and the fluid contains little besides sugar. The whey which is left after cheese-making, commonly answers the purpose, if clarified by beating it up with the white of an egg and subsequently boiling and filtering. Globules of oil must be separated as far as possible, or they will produce a greasiness of the paper.[50]
[50]See the Vocabulary, Part III,, Art. "Milk," for further particulars.
[50]See the Vocabulary, Part III,, Art. "Milk," for further particulars.
Salt the prepared Serum with Chloride of Sodium or Ammonium; in quantity about eight or ten grains to each fluid ounce, and render sensitive upon the same Bath as that recommended for the Citrate Process.
A NEGATIVE PRINTING PROCESS UPON IODIDE OF SILVER.
Iodide of Silver is more sensitive to the reception of the invisible image than the other compounds of that metal; and hence it is usefully employed in printingenlargedPositives from small Negatives, by means of the Camera. The great stability of the proofs upon Iodide of Silver will also be a recommendation of this process when unusual permanency is required.
Take of
The best paper to use will be either Turner's Calotype, or Whatman's or Hollingworth's Negative; the foreign papers do not succeed with the above formula (p. 258).
Float the paper on the iodizing Bath until it ceases to curl up and lies flat upon the liquid: then pin up to dry in the usual way.
Render sensitive upon a Bath of Aceto-Nitrate of Silver containing 30 grains of Nitrate of Silver with 30 minims of Glacial Acetic Acid to each ounce of water.
When the sheet is quite dry, place it in contact with theNegative in a pressure frame, and exposeto a feeble light. About 30 seconds will be an average time upon a dull winter's day, on which it would be impossible to print at all in the ordinary way. On removing the Negative nothing whatever is seen upon the paper, the image being strictly invisible in this process unless the exposure has been carried too far.
Develope by immersion in a saturated solution of Gallic Acid, prepared in the manner described atpage 261. The image appears slowly, and the process may last from 15 minutes to half an hour. If the exposure has been correctly timed, the Gallic Acid appears at length almost to cease acting; but when the proof has been over-exposed, the development goes on uninterruptedly, and the image becomes too dark, partaking more of the character of a Negative than a Positive. The usual rule, thatunder-exposed proofs develope slowly but show no half-tones, and that theover-exposed develope with unusual rapidity, is also observed in the process with Iodide of Silver.
After the picture is fully brought out, wash in cold, and subsequently in warm water, to remove the Gallic Acid, which, if allowed to remain, would discolour the Hyposulphite Bath. Then fix the Print in a solution of Hyposulphite of Soda, one part to two of water, continuing the action until the yellow colour of the Iodide disappears. The fixing Bath ought not to produce much change in the tint. If the Positive loses its dark colour on immersion in the Hyposulphite, and becomes pale and red, it has been insufficiently developed. The theory of this part of the process should be understood:—It is particularly thesecond stageof the development of a Photograph (see p. 144) on which the fixing Bath produces no effect; and therefore a considerable change of colour in the Hyposulphite indicates that too little Silver has been deposited, and the remedy will be to push the development, adding a little Aceto-Nitrate to the Gallic Acid if the strength of the Bath be found insufficient to yield dark tones.
The colour of Positives developed upon Iodide of Silver is not agreeable, and they become blue and inky when toned with gold. By fixing the proof in Hyposulphite of Soda which has been long used and has acquired sulphuretting properties, the tint is much improved; but the permanency of the Print under unfavourable conditions is lessened by adopting that mode of toning.
A NEGATIVE PRINTING PROCESS UPON BROMIDE OF SILVER.
By substituting the Bromide for the Iodide of Silver in the above process, the proportions and details of manipulation being in other respects the same, a more agreeable colour is obtained.
Paper prepared with Bromide of Silver is less sensitive than the Iodide, but an exposure of one minute (in the printing frame) will usually be sufficient even on a dull day. The image is nearly latent, but sometimes a very faint outline of the darkest shadows can be seen. The proportion of Bromide used is likely to influence this point; the sensitiveness being diminished, but the image showing more of the details before development, when the quantity of the Silver Salt is reduced to a minimum.
Either English or French papers may be used, but in the latter case the Bromide should be dissolved in Serum of Milk (p. 262), or it will be difficult to obtain a good surface picture. The proportion of Bromide may be five grains to the ounce of Serum.
These proofs, even when simply fixed in plain Hyposulphite of Soda, are superior in colour to the Positives printed by the last formula upon Iodide of Silver; and the permanency is very great if the development be sufficiently pushed. The use of the Serum of Milk gives an advantage in resisting the oxidizing influences to which Positives are liable to be exposed (p. 150).
GENERAL REMARKS ON NEGATIVE PRINTING.
Printing by development should not be attempted untilthe manipulation of the ordinary process by direct exposure to light has been acquired.
Perfect cleanliness is essential. The salting or iodizing solution and the Aceto-Nitrate Bath must be filtered clear, as the effect of small suspended particles in producing spots is more seen when the image is brought out by a developer.
It will be necessary to be far more careful in excluding white light than in the ordinary process; and when Iodide of Silver is used, all the precautions required in the case of Collodion Negatives must be taken.
Observe particularly that the dishes are kept clean, or the Gallo-Nitrate of Silver will be rapidly discoloured (read the remarks atpage 179).
Stereoscopic Negatives and small portraits are not successfully printed by development; since it is difficult to obtain the most elaborate definition, and there is a slight tendency to yellowness in the white parts. Positives may be developed upon Albumen paper, but the Gallic Acid is apt to discolour the lights.
In printing by development upon Chloride of Silver, the theory of the subject must be particularly studied. When the weather is cold and the light bad, the development of the image proceeds slowly, the Gallic Acid Bath remains clear, and good half-tones are obtained; but under opposite conditions, the developer may become turbid and the shadows be lost by excessive deposit of Silver. Thisover-developmentwill be remedied by printing the Negative in a more feeble light (near to the open window of a room), and by adding Acetic Acid to the developer, about 5 or 10 minims to the ounce, so as to bring out the image more slowly. The intensity of action is thus lessened, and if the picture be not under-exposed, the half-tones will be good.
Observe also when preparing papers with Citrate, that if too much Carbonate of Soda be added in neutralizing the Citric Acid, Carbonate of Silver will be deposited inthe paper, the effect of which is to remove by degrees the acidity of the Nitrate Bath, and to produce over-development and excessive sensibility to light.
The colour of the proofs when taken from the Gallic Acid should belight red; the gradation of tone not being usually so perfect when the development is carried into the second or black stage.
It is not recommended to prepare too large a stock of the salted papers, as they will probably be liable to mouldiness and decomposition unless kept perfectly dry.
SECTION III.
The Sel d'or Process for toning Positives.
This process is somewhat more troublesome than the plan of fixing and toning in one solution, but possesses advantages which will presently be enumerated. The description may be divided into the preparation of the toning Bath, and the manipulatory details.
THE PREPARATION OF THE TONING BATH.
Take of
Dissolve the Gold and Hyposulphite of Soda each in two ounces of the water; then mix quickly by pouring the former solution into the latter, and add the Hydrochloric Acid. If the Chloride of Gold be neutral, the liquid will have a red tinge, but ifacid, then the solution may be colourless. The commercial Chloride of Gold, containing usually much free Hydrochloric Acid, will not require any addition of that substance. (See the Vocabulary, Part III.)
In place of making an extemporaneous Hyposulphite of Gold by mixing the Chloride with Hyposulphite of Soda, the Crystallized Sel d'or may be used, adding about half a grain to the ounce of water, acidified as before; but the objection to the employment of this salt is its expense, and also the difficulty of obtaining it in a pure form; some samples containing less than five per cent, of Gold.
It will be found very convenient to keep the two solutions on hand ready for mixing, viz. the Chloride of Gold dissolved in water in the proportion of a grain to the drachm, and the Hyposulphite of Soda, three grains to the drachm. When required for use, measure out a fluid drachm of each, dilute with water to two ounces, and mix.
It is possible that the three-grain solution of Hyposulphite of Soda may by long keeping become decomposed, with precipitation of Sulphur. The effect of this would be to produce a turbidity and deposit of Gold on mixing the ingredients for the Bath, the Chloride of Gold being in excess over the Hyposulphite of Soda (seep. 250).
The Bath of Sel d'or is always most active when recently mixed, but it will keep good for some days if contact with free Nitrate of Silver be avoided. The addition of this substance produces a red deposit in the Bath, containing Gold, and the solution then becomes useless.
DETAILS OF MANIPULATION.
The paper may be prepared by either of the formulæ given in the first Section of this Chapter, according to the tint desired. The pure black tones are obtained most easily with the Ammonio-Nitrate paper, and the purple tints, without gloss, on paper prepared with plain Chloride and Citrate of Soda.
The printing is not carried quite to the usual intensity, as the half-tones are very little dissolved in this process.
On being taken from the frame, the prints are washed thoroughly in common water until it ceases to becomemilky; that is, until the greater part of the Nitrate of Silver has been removed. The washing must be conducted in a dark place, but it is not necessary to hasten it; the proofs may be thrown into a pan of water covered with a cloth, and allowed to remain until required for tinting.
A trace of free Nitrate of Silver usually escapes the washing; this would cause a yellow deposit on the Print, and also in the toning Bath. It must therefore be removed, either by adding a littlecommon saltto the water during the last washings, or by means of a dilute solution of Ammonia.
For plain paper Prints the former plan will be found the least troublesome; but with Albumen proofs[51]the Ammonia is required, in order to dissolve away a portion of the Albuminate of Silver which has escaped the action of light, before submitting the print to the gold; otherwise the dark tones would nearly disappear in the fixing Bath, the Hyposulphite carrying away the Gold with this superficial layer of silver salt.
[51]The amateur is recommended not to use Albuminized paper in this process until he has become accustomed to the manipulations; the plain paper prints being toned with more ease and certainty.
[51]The amateur is recommended not to use Albuminized paper in this process until he has become accustomed to the manipulations; the plain paper prints being toned with more ease and certainty.
To prepare the Ammonia Bath, take of
The exact quantity is not material; if the liquid smells faintly of Ammonia, it will be sufficient. Place the washed Prints in this Bath, two or three at a time, and allow them to remain until the purple tint gives place to a red tone. The action must be watched, because if the Ammonia Bath be strong, the proof becomes unusuallypale and red, and when this is the case a little brilliancy is lost in the after-tinting.
As the Print is comparatively insensitive to light when the excess of Nitrate has been washed away, it is not necessary to darken the room; but abright lightproceeding from an open door or window should be avoided.
After using the salt or the Ammonia, soak the Prints again for a minute or so in common water. Then place them in the toning Bath of Gold and acid; do not put in too many at once, and move them about occasionally, to prevent spots of imperfect action at the point where the sheets touch each other.
The foreign papers, plain salted, colour rapidly in two or three minutes. English papers require five to ten minutes; Albuminized, ten minutes to a quarter of an hour. The tendency of the Gold Bath is to give a blue tone to the image; hence proofs which are light red after using the salt or Ammonia, become, first red-purple, and then violet-purple in the Sel d'or. Albumen Prints assume some shade of brown, or of purple if not too strongly Albuminized. Ammonio-Nitrate papers highly salted, and prepared without Citrate, become first dark purple, and then blue and inky; the Citrate is intended to obviate this inky tint.
When the darkest tones are reached, the Bath produces no further effect, but eventually (more especially if the solution be not shielded from light [?]) there is a little decomposition, producing a cream-coloured deposit upon the lights.
The toning being completed, the Prints are again washed for an instant in water, to remove the excess of gold solution. This washing must not be continued longer than two or three minutes, or there will be danger of yellowness of the whites; this however ought not to happen with proper precautions.
Lastly, the proofs are fixed in a solution of Hyposulphite of Soda, one part to four of water; which may be used many times successively. This Bath alters the tone very little if the deposit of Gold be well fixed on the Print; but the writer has often observed in the case of Albumen paper and paper prepared with Citrate (Formula II.) that if removed too quickly from the Sel d'or, the purple tones change by immersion in the Hyposulphite to a chocolate-brown. Ammonio-Nitrate Prints are less liable to alter in this way.
In order that the fixing may be properly performed, the time of immersion should not be less than ten minutes with a porous paper, plain salted; or fifteen minutes in the case of an English or albuminized paper.
Ammonia may be used for fixing plain paper Prints; about one part of the Liquor Ammoniæ, to four of water. Ten minutes' immersion will usually be sufficient, and the tone is very little affected. This process is a good one, but the pungent smell of the Ammonia is an objection, and the Bath discolours by use. Some care too is required in order to ensure a proper fixing of the prints (see the remarks atpage 131).
For directions to wash and mount the proofs, seepage 255.
It will sometimes happen in the Sel d'or process, from the toning Bath having but little solvent action on the light shades, that the Prints, after being washed and dried, appear too dark; this may be remedied by laying them for a few minutes ina very dilute solutionof Chloride of Gold (five or six drops of the yellow solution of the Chloride to a few ounces of water) and washing for an additional quarter of an hour. Or an over-printed Positive may be saved by toning it with Chloride of Gold instead of Sel d'or. In that case, after proper removal of the free Nitrate of Silver, a few drops of a lemon-yellow solution of Chloride of Gold (with a fragment of Carbonate of Soda added to remove acidity,p. 132), should be poured over the Print, which is to be subsequently fixed in the usual way.
Advantages of toning by Sel d'or.—This process will be found especially useful by those who print large Positives. The solutions may be mixed in a few minutes, and, being very dilute, are economical. It is not even necessary to employ aBathfor toning, but if the Sel d'or solution be prepared of about twice or three times the strength given in the formula, it will be sufficient to pour a few drachms upon the surface of the print. As the Gold solution is always used soon after mixing, a uniform and permanenttint can be obtained; whereas the single fixing and toning Bath of Gold and Hyposulphite loses much of its efficacy by keeping, andover-printingof the proof is required in proportion as the Bath becomes older.
SECTION IV.
On a mode of Printing enlarged and reduced Positives, Transparencies, etc., from Collodion Negatives.
To explain the manner in which a Photograph may be enlarged or reduced in the process of printing, it will be necessary to refer to the remarks made atpage 52, on theconjugate fociof lenses.
If a Collodion Negative be placed at a certain distance in front of a Camera, and (by using a tube of black cloth) the light be admitted into the dark chamber only through the Negative, a reduced image will be formed upon the ground glass; but if the Negative be advanced nearer, the image will increase in size, until it becomes first equal to, and then larger than, the original Negative; the focus becoming more and more distant from the lens, or receding, as the Negative is brought nearer.
Again, if a Negative portrait be placed in the Camera slide, and the instrument being carried into a dark room, a hole be cut in the window-shutter so as to admit light through the Negative, the luminous rays, after refraction by the lens, will form an image of the exact size of life upon a white screen placed in the position originally occupied by the sitter. These two planes, in fact, that of the object and of the image, are strictlyconjugate foci, and, as regards the result, it is immaterial from which of the two, anterior or posterior, the rays of light proceed.
Therefore in order to obtain a reduced or enlarged copy of a Negative, it is necessary only to form an image of the size required, and to project the image upon a sensitive surface either of Collodion or paper.
A good arrangement for this purpose may be made by taking an ordinary Portrait Camera, and prolonging it in front by a deal box blackened inside and with a double body, to' admit of being lengthened out as required; or, more simply, by adding a framework of wood covered in with black cloth. A groove in front carries the Negative, or receives the slide containing the sensitive layer, as the case may be.
InreducingPhotographs, the Negative is placed in front of the lens, in the position ordinarily occupied by the object; but in making an enlarged copy, it must be fixedbehindthe lens, or, which is equivalent, the lens must be turned round, so that the rays of light transmitted by the Negative enter the back glass of the combination, and pass out at the front. This point should be attended to in order to avoid indistinctness of image from spherical aberration.
A Portrait combination of lenses of 2½ or 3¼ inches diameter is the best form to use, and the actinic and luminous foci should accurately correspond, as any difference between them would be increased by enlarging. A stop of an inch or an inch and a half aperture placedbetweenthe lenses obviates to some extent the loss of sharp outline usually following enlargement of the image.
The light may be admitted through the Negative by pointing the Camera towards the sky; or direct sunlight may be used, thrown upon the Negative by a plane reflector. A common swing looking-glass, if clear and free from specks, does very well; it should be so placed that the centre on which it turns is on a level with the axis of the lens.
The best Negatives for printing enlarged Positives are those which are distinct and clear; and it is important to use asmallNegative, which strains the lens less and gives a better result than one of larger size. In printing by a 2¼ lens for instance, prepare the Negative upon a plate about two inches square, and afterwards enlarge it four diameters.
Paper containing Chloride of Silver is not sufficientlysensitive to receive the image, and the Print should be formed upon Collodion, or on iodized paper developed by Gallic Acid (seep. 263).
The exposure required will vary not only with the intensity of the light and the sensibility of the surface used, but alsowith the degree of reduction or enlargement of the image.
In printing upon Collodion the resulting picture is Positive by transmitted light; it should be backed up with white varnish, and then becomes Positive by reflected light. The tone of the blacks is improved by treating the plate first with Bichloride of Mercury, and then with Ammonia, in the manner described at pages 113 and 207.
Mr. Wenham, who has written a paper on the mode of obtaining Positives of the life size, operates in the following way:—he places the Camera, with the slide containing the Negative, in a dark room, and reflects the sunlight in through a hole in the shutter, so as to pass first through the Negative and then through the lens; the image is received upon iodized paper, and developed by Gallic Acid, in the mode described in the second Section of this Chapter (p. 263).
On printing Collodion transparencies for the Stereoscope.—This may be done by using the Camera to form an image of the Negative in the mode described in the last page; but more simply by the following process:—Coat the glass, upon which the Print is to be formed, with Collodio-Iodide of Silver in the usual way; then lay it upon a piece of black cloth, Collodion side uppermost, and place two strips of paper of about the thickness of cardboard and one-fourth of an inch broad, along the two opposite edges, to prevent the Negative being soiled by contact with the film. Both glasses must beperfectly flat, and even then it may happen that the Negative is unavoidably wetted; if so, wash it immediately with water, and if it be properly varnished, no harm will result.
A little ingenuity will suggest a simple framework ofwood, on which the Negative and sensitive plate are retained, separated only by the thickness of a sheet of paper; and the use of this will be better than holding the combination in the hand.
The printing is conducted by the light of gas, or of a camphine or moderator lamp; diffused daylight would be too powerful.
The employment of a concave reflector, which may be purchased for a few shillings, ensures parallelism of rays, and is a great improvement. The lamp is placed in the focus of the mirror, which may at once be ascertained by moving it backwards and forwards until an evenly illuminated circle is thrown upon a white screen held in front. This in fact is one of the disadvantages of printing by a naked flame—that the light falls most powerfully upon the central part, and less so upon the edges, of the Negative.
The picture must be exposed for a longer or shorter time (about ten seconds will be an average) according to its behaviour during development (see p, 224); this process, as well as the fixing, is conducted in the same manner as for Collodion pictures generally.
Some adopt the plan of whitening by Corrosive Sublimate, and again blackening by dilute Ammonia, as an improvement to the colour of the dark shadows (seep. 113).
If this mode of printing upon Collodion be conducted with care, the Negative being separated from the film by the smallest interval only, the loss of distinctness in outline will scarcely be perceived.
Stereoscopic transparencies may also be printed by the dry Collodion process described in Chapter VI., or by the Collodio-Albumen process. Mr. Llewellyn recommends the employment of a solution of Oxymel, so dilute that the plate becomes nearly dry, and may be laid in contact with the Negative without fear of injury (see the footnote atpage 302).
CLASSIFICATION OF CAUSES OF FAILURE IN THE COLLODION PROCESS.
Section I.—Imperfections in Collodion Photographs.Section II.—Imperfections in Paper Positives.
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, orthe 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 atpage 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 atp. 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 anddecomposed 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, placeit 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 Transparencymay generally be traced to some causewhich 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 developerimmediately; 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 developerhas 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.