SECTION II.. _formulæ, Etc., for Negative Solutions._[34]

Formulæ, etc., for Negative Solutions.

The same Collodion and Nitrate Bath may be used both for Positives and Negatives if required; but there are a few minor points of difference which are included in the following remarks.

THE COLLODION.

FORMULA No. 1.

Purified Ether, sp. gr. ·720 5 fluid drachms. Purified Alcohol, sp. gr. ·825 3 fluid drachms. Soluble Pyroxyline 4 to 8 grains. Pure Iodide of Cadmium or Ammonium 4 to 5 grains.

FORMULA No. 2.

Rectified Ether, sp. gr. ·750 6 fluid drachms. Alcohol, sp. gr. ·836 2 fluid drachms. Soluble Pyroxyline 4 to 8 grains. Iodide of Potassium or Ammonium 4 grains.

When the Collodion and Iodizing mixture are kept separate, the second formula will stand thus:--

Rectified Ether ·750 3 fluid ounces. Alcohol of ·836 2 fluid drachms. Pyroxyline 15 to 30 grains.

To each fluid ounce of this plain Collodion add 2 fluid drachms of the following Iodizing solution:--

Alcohol, sp. gr. ·836 1 fluid ounce. Iodide of Potassium 20 grains.

When the temperature of the Nitro-Sulphuric Acid used in making the Pyroxyline is high (140° to 155°), it often happens that the Collodion is too fluid with 4 grains of soluble paper to the ounce, and forms a blue transparent film of Iodide on dipping the plate in the Bath. In that case, increase the quantity of Pyroxyline from 4 grains to 6, or even to 8 grains to each ounce.

If the Collodion is glutinous, and produces a wavy surface, with less than 4 grains of Pyroxyline to the ounce, it is probable that the Alcohol is too weak, or that the soluble Cotton is badly made.

If flakes of Iodide of Silver are seen loose upon the surface of the film, and falling away into the Bath, the Collodion is over-iodized, and it will be impossible to obtain a good picture.

After the Collodion has been employed to coat a number of plates, the relative proportions of Alcohol and Ether contained in it become changed, from the superior volatility of the latter fluid: when it ceases to flow readily, and gives a more dense film than usual, thin it down by the addition of a little rectified Ether.

In dissolving the Pyroxyline, any fibrous or flocculent matter which resists the action of the Ether, must be allowed to subside, the clear portion being decanted for use. The Iodide of Potassium is to be finely powdered, and digested with the spirit until dissolved; it is better not to apply any heat. Both Iodide of Ammonium and Iodide of Cadmium dissolve almost immediately, if the salts are pure.

The Collodion must be kept in a cool and dark place. When prepared with Iodide of Ammonium or Potassium it becomes at length high coloured and insensitive. The free Iodine may then be removed by a strip of pure zinc or silver-foil.

When sensitiveness is not an object, many prefer working with an old, coloured Collodion, finding that it gives more intensity. It has been shown at page 97 that a peculiar change takes place in Collodion after iodizing, by which the intensity of the image is increased.

Directions for using Glycyrrhizine in Collodion.--The action of this material has been described at page 114. The Collodion should be iodized with the Iodide of Cadmium only, or with a mixture of the Iodides and Bromides of the alkalies. The condition which calls for the employment of Glycyrrhizine is that often found in a newly made and rather glutinous Collodion, viz. sensitiveness of film, with good half-tones, but insufficient intensity in the high lights. Dissolve the Glycyrrhizine in Alcohol (not Methylated) in the proportion of 5 grains to the ounce: this solution may perhaps keep unchanged for three or four months. To each ounce of the Collodion add from one to four drops, and expose in the Camera a few seconds longer than before. The effect of the Glycyrrhizine upon the Collodion may not be fully produced immediately; if so, the fluid must be set aside for twenty-four hours.

Use of Nitro-glucose in Collodion.--Nitro-glucose is a substance analogous to Pyroxyline, but more unstable. When added to Collodion iodized with the alkaline Iodides, it slowly decomposes, liberates Iodine, lessens the sensitiveness to a certain extent, and confers intensity. Like Glycyrrhizine, it may be used to remedy feebleness of the image, and to give opacity to the blacks. Prepare the Nitro-glucose by the directions given in the Vocabulary, Part III. Dissolve twenty grains in an ounce of pure spirit, and agitate with powdered chalk to remove free acid. Add from five to eight drops to each ounce of Collodion. In a few days, more or less, according to temperature, the Collodion will deepen in colour, and will be found on trial to produce a more vigorous picture.

Collodion for hot Climates.--In this case the Iodide of Ammonium should be avoided, as unstable and prone to change colour. Iodide of Cadmium may be substituted, which has been shown to remain quite colourless when dissolved in Alcohol and Ether.

Collodion iodized with the Iodide of Potassium will usually keep for about six weeks or two months; but no certain rule can be given, much depending upon the condition of the Ether and the heat of the weather.

Plain Collodion may retain its properties unimpaired for five or six months, sometimes much longer; but there is a tendency to a formation of the acid principle (p. 85); and hence, on the addition of an alkaline Iodide to old Collodion, the coloration is commonly very rapid. The structure of the transparent film may also be injured by keeping plain Collodion for too long a time.

Photographers who wish to operate with Collodion in hot climates will find it advantageous to carry with them the prepared Pyroxyline and the spirituous solvents, observing that the bottles are carefully luted, and that a bubble of air is left in the neck of each, to allow for the necessary expansion, which might otherwise burst the glass or force out the stopper.

THE NITRATE BATH.

This solution may be prepared by the same formula as that given for direct Positives at page 203, acidifying the solution with Acetic Acid in preference to Nitric Acid.

THE DEVELOPING SOLUTION.

Pyrogallic Acid 1 grain. Acetic Acid (glacial) 10 to 20 minims, or Beaufoy's Acetic Acid fort. 1 fluid drachm. Alcohol 10 minims. Distilled Water 1 fluid ounce.

In place of Distilled Water, pure Rain-Water may be used (see Part III., Art. "Water").

The quantity of Acetic Acid required will vary with the strength of the Acid and the temperature of the atmosphere. An excess enables the manipulator to cover the plate more easily before the action begins, but when the picture is taken in a dull light, is apt to give a bluish, inky hue to the image. In cold weather, use less of the Acetic and twice the quantity of Pyrogallic Acid. With Collodion prepared from Spirits nearly anhydrous, and iodized with Iodide of Cadmium, the full quantity of Acetic Acid will be required, as there is sometimes a little difficulty in making the developer flow up to the edge of the film.

If the image cannot be rendered sufficiently black, two or three minims of the Nitrate Bath solution may be added to each drachm towards the end of the development.

If the solution be kept for some time after its first preparation, it becomes brown and discoloured. In this state it will still develope the image, but is less likely to give a clear and vigorous picture. A solution of Pyrogallic Acid in Acetic Acid will keep for many weeks, and may be diluted down when required for use.

The following is a good formula:--

Pyrogallic acid 12 grains. Beaufoy's Acetic acid 1 fluid ounce.

To one drachm add seven drachms of water.

THE FIXING LIQUID.

Cyanide of Potassium 2 to 12 to 20 grains. Water 1 fluid ounce.

or, Hyposulphite of Soda 1/2 ounce. Water 1 fluid ounce.

For remarks on the Cyanide of Potassium Fixing Bath, see the last Section, page 207.