Read Ebook: Photo-engraving Photo-etching and Photo-lithography in Line and Half-tone Also Collotype and Heliotype by Wilkinson W T Wilson Edward L Edward Livingston Editor

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Now filter the purified water and use it for compounding the nitrate of silver bath, but do not use it for any other purpose.

The strength of a nitrate of silver bath, for line work, should be thirty grains of nitrate of silver to each ounce of water, and should not be allowed to fall below twenty-five; and for half-tone negatives, nitrate of silver should be thirty-five, and not lower than thirty grains to the ounce.

Be sure to keep all funnels, bottles, and dishes used for the silver bath, separate and distinct from all others, and never use them for any other purpose. |14|

THE NITRATE OF SILVER BATH .

In the ancient days of photography, when, to say it was possible to prepare a dry plate nearly as sensitive as a wet collodion plate, was to excite the risible faculties of the audience, the above heading might almost always be seen in the journals, and the amount of matter written under that heading would fill many good-sized volumes. Some writers went into the subject in a very elaborate manner, whilst others would counsel very simple methods of preparation and management.

When the solution is perfectly clear and bright, pour sufficient into a perfectly clean porcelain, glass, or papier-mach? dish, then take a clean plate and coat it with collodion; close the door of the dark-room, and when the film of collodion is perfectly set, raise one end of the dish containing the silver solution, place one edge of the collodionized plate against the bottom of the upper edge of the dish, then drop the plate upon the bottom of the dish, and at the same time lower the dish; by this means the silver solution will flow in an even wave over the surface of the collodionized plate; now place the cover on the dish so as to exclude light and dust, and allow the plate to remain in the solution for five minutes, then with a silver hook lift the plate from the solution, and allow it to drain ; when the plate has drained so that no solution drips from it, place it into the carrier of the dark slide; then close the dark slide and let it remain there for five minutes, at the end of which time remove the plate to the sink, and flood it with sufficient developer to just cover the film; keep this solution flowing, to and fro, over the |15| plate for the space of two minutes, then wash it under the tap until the surface is no longer greasy; then apply the fixing or clearing solution until the whole of the yellow bromo-iodide is dissolved away; again wash, and take the plate into the daylight.

Now comes the test; if the film is perfectly transparent, and clear as the glass itself, the bath is all right; but if there is the slightest deposit , then the solution will require the addition of a little nitric acid. After this stir it well, and after a rest of an hour or two try again, repeat the addition of the nitric acid, and try a plate; repeat until the film, after developing, washing, and fixing, is perfectly clear, and free from deposit and fog.

The bath is now in proper working order, and if reinforced after each day's work with a sufficient quantity of saturated solution of nitrate of silver , kept free from contamination with other chemicals, and carefully filtered occasionally, it will remain in good working order for at least six months, and then may be renewed by treating as directed on page 12.

It will sometimes happen, notwithstanding that extreme care and cleanliness is exercised in the management of the bath, that it will not work properly, and the reason why cannot easily be discovered. In such a case, steps must be taken to put the solution into working order.

In the case of rectifying a disordered bath, there are many methods of procedure, but the simplest, and, as a rule, the most certain method, is to render the solution alkaline by the addition of liquor ammonia, adding the ammonia a little at a time; then, after well shaking, test it with red litmus paper and continue the addition of ammonia until the red litmus paper is turned blue. In this alkaline condition the solution should be poured into a large flat dish, and exposed to the action of the sun. That will speedily reduce and throw down in the form of a black precipitate, any organic matter that may be in the bath, and at the same time the heat of the sun will cause evaporation of the ether and alcohol left in the solution by the collodion plates.

The bath solution should be exposed to the sun for two or three days, or until such time as suffices to render the solution clear, and the precipitate entirely separated out. But this cannot take place unless the solution is decidedly alkaline, the presence of acid stopping the action of light.

Do not be in a hurry about doctoring a bath solution , but give the light plenty of time to reduce the organic matter, and also to |16| volatilize the ether and alcohol; then filter the solution through filtering paper , as if it is attempted to filter through a pledget of cotton-wool the fine precipitate of organic matter quickly clogs the wool and stops the filtering.

The doctored solution being filtered, test it with a piece of perfectly fresh, blue litmus paper, and add nitric acid, drop by drop--shaking well between the additions of acid--until the blue litmus paper just turns red. Do not add acid sufficient to make the litmus turn violently red, unless the bath is for line negatives, as a bath for half-tone negatives must be only just acid, whereas a bath for line work must contain more acid.

If the color of the litmus paper shows that the alkali has been neutralized, a plate is collodionized, then immersed in the bath for five minutes, then drained, and placed in the dark slide, or in a dark box for five minutes, then flooded with the iron developer ; if, upon the application of this the film should turn black, add more nitric acid, stir up thoroughly, then try again, repeating the trials until, upon fixing the plate with the solution of cyanide of potassium, the film of collodion is left upon the glass plate as clear as it was before it was immersed in the silver bath.

A little above here it is stated that less nitric acid is required in the bath for half-tone negatives than for line work, and the question may well be asked where may the line be drawn? The reply is that, for half-tone work, a piece of blue litmus paper should, upon immersion into the solution, turn red very slowly, but when the bath is required for line negatives the blue litmus may at once indicate the presence of acid.

After a bath solution has been renovated in the above manner, it should be tested for strength, either by the volumetric method , or by means of the ordinary argentometer sold by the dealers, and, if, after testing, the strength is shown to be too great, dilute with a sufficiency of sunned water ; and if not sufficiently strong, add crystals of nitrate of silver to make up the strength to thirty or thirty-five grains per ounce.

A bath solution renovated as above, will generally be found to work cleaner, and yield brighter negatives than a new solution, and it will also, if carefully used, last longer; but it must be kept up to a proper working strength by the occasional addition of a little of a saturated solution of nitrate of silver.

The fact that the strength of the silver solution has got too low is shown by the presence of semi-opaque, fantastic markings near the thick edge of the collodion film, and also in conjunction with the presence of organic matter in |17| the deposition under the surface of the film of an extremely fine sand-like deposit, which, in the fixed negative, develops into myriads of pinholes in the densest portions of the image.

THE DEVELOPING SOLUTION.

First purchase seven pounds of commercial sulphate of iron and put this into a gallon jug, and fill it up with boiling water ; stir with a clean rod at short intervals for three or four hours, then allow to stand until the sediment settles, and the top portion of the solution is clear and bright; then decant as much as possible into a bottle or bottles, and label "Saturated Solution of Iron." Then again fill up the jar with boiling water, stir until as much as possible is dissolved, so as to be ready by the time the stock in the bottle is exhausted, and repeat the process until all the crystals are dissolved; then wash out the jar, reject the residue, and begin again.

But bear in mind that, unless there are crystals left in the solution after each addition of hot water, it will not be saturated; therefore, before taking the solution into use, be sure there are undissolved crystals in the jar.

For use, take of

Saturated Solution of Iron 10 ounces. Acetic Acid 4 ounces. Water 70 ounces. Alcohol 1 ounce to 5 as required.

In the above solution, the alcohol is added to enable the developer to readily assimilate with the sensitive film, and the quantity requisite varies with the age of the silver bath, or, to be more correct, with the quantity of plates sensitized therein. At first, little or no alcohol will be required, but after a number of plates have been sensitized the developer refuses to flow evenly, and seems disposed to run over the edges of the plate; this is a sign that more alcohol is required, and when more has been added the developer will flow evenly as before; but when 80 ounces of developer require over 4 ounces of alcohol to make it flow, it is a pretty sure sign that the bath wants remaking.

The developer is applied to the plate after exposure, from a straight-lipped cup, or glass measure, which should be kept for the exclusive use of this solution, as the mixture of any of the other solutions with it will at once counteract its working power. |18|

Cyanide of Potassium 3 ounces. Water 20 ounces.

This solution is highly poisonous, both in solution and vapor, so it ought to be kept in an upright holder, the plate being lowered into the solution on a dipper; keep the solution well covered up, so as to prevent evaporation as much as possible.

After being in use a short time this solution will become weak and should be strengthened by the addition in the evening of a lump or two of cyanide and then stirred up with the dipper in the morning; the negative must not be left in this solution too long or the density of the film will be impaired, but must be removed and well washed directly all the yellow iodide has been dissolved.

THE INTENSIFIER.

No. 1.

Water 80 ounces. Chloride of Ammonium 2 ounces.

dissolve, then add:

Bichloride of Mercury 2 ounces.

dissolve, and filter.

No. 2.

Liquor Ammonia 0.880 5 ounces. Water 20 ounces.

Solution No. 1 is best kept in an upright holder, as if kept in a flat dish there is always the danger of cutting the skin with the glass plate and getting the mercurial poison into the system.

No. 2 is kept in a well-stoppered bottle and only sufficient for each plate withdrawn as required.

Another method of intensifying, for those who object to the use of mercury, is to bleach the negative in a solution of

Ferridcyanide of Potassium 6 parts. Nitrate of Lead 4 parts. Water 80 parts.

dissolve and filter. |19|

When the plate is bleached, wash it thoroughly under the tap, taking care that the edges and corners of the film as well as the centre are washed, then flood it with a sufficient quantity of

Nitric Acid 1 ounce. Water 80 ounces.

Allow this to remain on a few seconds, then wash, and flood with a sufficient quantity of

Sulphide of Ammonium 1 part. Water 5 parts.

which will at once turn the film an intense black; again wash, and flood with the nitric acid solution, and again wash; then the negative is allowed to dry.

This method of intensifying is cheaper than the other, and if the washes of acid between and after the other two solutions are carefully done, and the stench of the sulphide is not objected to, then there is little or no difference in the results; but if the acid washes are omitted or the sulphide has not been kept corked, and is consequently not fresh, then there is great danger of a brown stain upon the lines, which is more or less fatal to getting a good print on zinc.

For half-tone negatives, instead of fixing or clearing with the cyanide of potassium, the developer is washed off directly, and then they are intensified at once by the application of a mixture of pyrogallic acid, citric acid, and nitrate of silver, as follows:

No. 1 Solution of Pyrogallic Acid 40 grains. Citric Acid 30 grains. Water 20 ounces.

As much of this solution as will cover the washed plate is put into a small cup, and flowed all over the film, then returned to the cup, and a few drops of

Nitrate of Silver 30 grains. Water 1 ounce.

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