Cooley's Cyclopaedia of Practical Receipts Volume Ii Part 132

_Sensitising Solution_ (_for Paper_). Nitrate of silver, 5 dr.; distilled water, 5 oz.; nitric acid, 2 drops; kaolin, 1 oz. Dissolve the nitrate of silver in the water, and then add the acid and kaolin; the kaolin will not dissolve, its use being to prevent the solution becoming discoloured after using. This solution will not require filtering; it must be allowed to become quite clear, and when required for use must be carefully decanted.

This solution should be occasionally tested with the argentometer, and sufficient nitrate of silver added to restore it to its original strength.

_Another Negative Collodion._ Ether, 1/2 oz.; gun-cotton, 7 gr.; bromide of cadmium, 1/2 gr.; bromide of ammonium, 1-1/2 gr.; iodide of calcium, 1 gr.; iodide of pota.s.sium, 1 gr.; iodide of ammonium, 1 gr. For intensifying, flood with chloride of gold, 1 gr.; water, 15 oz.; then wash, and flood with pyrogallic acid, 2 gr.; water, 3 oz.

_Toning Baths._ 1. Chloride of gold, 4 gr.; acetate of soda, 1/4 oz.; distilled water, 10 oz.; dissolve and filter. 2. _To produce black to bright sepia tones, according to length of immersion._ Take carbonate of soda sufficient to cover a threepenny piece, dissolve it in a teaspoonful of cold water in a cup, add 2 gr. of chloride of gold, then add 3 oz. of boiling water; use in 15 minutes. This will suit Hart's alb.u.minised paper.

_Fixing Solution_ (_for Paper Prints_). Hyposulphite of soda, 8 oz.; distilled water, 1 pint. This solution must only be used once.

_Stopping-out Negatives._ Small, round, transparent spots are frequently found on gla.s.s negatives, which, if not stopped, occasion corresponding black spots on the print. Lay the plate on a slab of gla.s.s, having either direct or reflected light shining up through it. Then cover the spots with a mixture composed of 10 parts of ivory black, 2 parts of saturated solution of gum Arabic, 2 parts of white honey, 1 part of sugar-candy; well mix and apply with a fine camel-hair brush. Should the spots on the negative be black or opaque, white spots will be formed on the print; these are easily tinted with a little water colour, to match the other portions of the print; it is seldom necessary, therefore, to alter the negative on this account.

_Ferrotypes._ In these, instead of a gla.s.s plate being used to receive the picture, as in a positive gla.s.s photograph, a thin plate of black varnished iron is employed. Of course no black backing is required; with this exception the photograph is produced in every particular by the same means and in the same manner as the gla.s.s positive is.

_To Clean Gla.s.s Plates._ (Mr Hughes.) The description of gla.s.s known as "flatted crown" is well suited for positives, but before using it requires careful cleaning. The sharp edges should be first removed with a "corundum" file, or by drawing the sharp edge of one piece over the sharp edge of another; then place the gla.s.s on a clean flat surface, or put it in "a plate-cleaning holder," and pour a few drops of the plate-cleaning solution in the middle. Rub it carefully over every part with a bit of clean soft rag; turn the gla.s.s over, and do the other side the same. Then polish each side with a clean cloth, and finish with a soft chamois leather kept expressly for this purpose. Now breathe on the gla.s.s, and if the breath deposits evenly the plate is clean. If the plate, however, shows patches and marks, it must be recleaned. Let the edges be carefully wiped, and the plate is ready for use.

The following preparation makes a good plate-cleaning solution for gla.s.ses that require mechanical friction to make them clean:--Ordinary water, 5 oz.; alcohol, 5 oz.; iodide of pota.s.sium, 15 gr.; iodine, 3 gr. When dissolved, add tripoli, prepared chalk, whiting, or rotten-stone, in sufficient quant.i.ty to make a creamy paste.

This thin pasty solution is to be rubbed on the plates on both surfaces and polished off as already described. This amount of cleaning will generally be sufficient for new gla.s.ses, but when they have been used they require more labour.

They must then be well washed under the tap, to get rid of all collodion and chemicals, and be wiped on cloths kept expressly for the purpose.

Should the plates have been varnished they must be soaked for some hours in a saturated solution of washing soda till the varnish and film come freely off. The gla.s.ses must then be immersed for a few minutes in a solution composed of common nitric acid, 2 oz., water, 10 oz., and be well washed and treated as already described. It is a good plan when working to have a dish of water at hand, and to place the spoilt pictures in it at once while they are wet, and at the end of the day to wash the gla.s.ses and put them away clean. By thus not allowing the films to dry on the gla.s.ses they are much easier cleaned, and fewer failures will arise from dirty gla.s.ses.

Collodion is a good material for cleaning gla.s.ses when they are not very dirty. Pour a few drops on the gla.s.s and well rub it with a clean cloth, and you will entirely remove all grease; a hint may thus be taken how to use up waste collodion.

_Various Solutions used in the Dry Process._ These are employed in cases where bromo-iodised collodion and the nitrate bath are used.

In all processes in which the bromo-iodised collodion is employed 2 grains of bromide of cadmium should be added to each ounce of the collodion.

Mr Bartholomew advises diluted alcohol to be poured over the plate previous to developing.

_Acid Pyro Developer._ This developer is formed as follows:

Pyrogallic acid 1 gr.

Glacial acetic acid 30 minims.

Water 1 oz.

The plate, after being wetted with dilute alcohol and washed, has this solution flowed over it, to which has been added 2 or 3 drops of a 10-grain nitrate of silver solution.

_Plain Pyro Developer._ The strength of this may vary from 1 to 5 gr. in an ounce of water. Two grains may be taken as a medium. The dry plate being flooded with alcohol and water, and washed so as to well wet the film, this solution is floated over it.

_Alkaline Pyro Developer._

No. 1.--Pyrogallic acid 96 gr.

Absolute alcohol 1 oz.

No. 2.--Carbonate of ammonia 96 gr.

Water 1 oz.

No. 3.--Bromide of pota.s.sium 10 gr.

Water 1 oz.

At the time of using, make up the following solution:

Water 1 oz.

Solution No. 1 10 minims.

Solution No. 3 5 "

Pour this over the wetted plate, allow it to remain on a few seconds only, and then pour back into the developing cup, and add to it 5 minims of solution No. 2, and apply again.

_The Collodio-Alb.u.men Dry Process._ (Mr Mudd.) In this process the ordinary bromo-iodised collodion is employed. The plate being sensitised is washed well first with distilled, then with common water, and placed in a dish half filled with solution of iodide of pota.s.sium (3 gr. to the oz.), and allowed to remain while the next plate is being prepared. It is then removed from the solution and well washed with clean water, after which the following solution is poured over its surface:

Distilled water 2-1/2 oz.

White of eggs 10 oz.

Iodide of pota.s.sium 50 gr.

Bromide of ammonium 10 gr.

Strongest solution of ammonia 120 minims.

Introduce these materials with some pieces of broken gla.s.s into a bottle capable of holding twice the quant.i.ty, and agitate till the whole forms a froth, and then, when settled, it is ready. A piece of camphor placed in the solution will help to preserve it. It must be filtered before using.

After the plate has been coated with the above it is finished by drying before the fire.

In this process all the above operations may be performed in ordinary white light. To render the plate sensitive, heat it as hot as the hand will bear, and when cool immerse it again in the following aceto-nitrate of silver bath for one minute, using only a yellow light, then wash thoroughly in clean water, and dry in the dark.

Nitrate of silver 30 gr.

Distilled water 1 oz.

Glacial acetic acid 1/2 dram.

The development may be commenced by either plain or alkaline pyro; Mr Mudd gives the preference to the plain, and intensifying after with acid silver.

Dr RYLEY'S _Modified Collodio-alb.u.men Dry Process_. In this method the plate has to be sensitised as usual, and washed thoroughly. When the plate has been well drained, and while still wet, it is coated with the following solution:

Alb.u.men 1 oz.

Water 2 oz.

Ammonia 30 minims.

The solution is beaten to a froth, allowed to settle, and filtered before using. Pour sufficient over the plate to cover it, letting it flow backwards and forwards so as to soak into the film. Pour the alb.u.minous solution away and thoroughly wash the plate, the last rinsing being with distilled water. Let the plate dry; when perfectly dry, moisten the plate with distilled water, and pour over the following solution:

Gallic acid 2 gr.

Water 1 oz.

Filter the solution before using. Pour it on and off the plate to well permeate the film, then set the plate up to drain, and dry without washing off the gallic acid solution. When the surface is dry finish by the heat of a dull fire.

_Bromide of Silver, Wet Process._ To every ounce of good collodion add 8 gr. of bromide of cadmium. The nitrate bath must be made 80 gr. to the oz., and slightly acidulated with nitric acid. The plate must remain in the bath the full time it requires to form a dense opaque film. When the plate is ready (it must not be removed from the bath until the film is much denser than in the ordinary wet process) it must be washed thoroughly to remove all silver. It must then have poured over it a 3-grain solution of gelatin made slightly alkaline with carbonate of soda, or diluted alb.u.men (alb.u.men, 1 oz.; water, 4 oz., well beaten together). When the plate is in this condition it may be exposed wet, or it may be allowed to dry. Prior to development it must be well washed, and the alkaline method must always be adopted. If the plates are used dry, a preliminary coating of dilute alb.u.men is necessary, but if used wet, this is not necessary.

_Bromide of Silver, Emulsion Process._ By this method the nitrate bath is not necessary, as the sensitive material is contained in the collodion.

The purchase of the material ready-made for working this process is recommended in preference to its direct manufacture, as its preparation demands the use of considerable technical skill, together with the employment of a gun cotton not usually attainable. Mr Hughes says the 'Liverpool Dry Plate Company' supply an excellent emulsion. It is only necessary to pour the emulsion on to a plate and to allow it to dry, when the plate is ready for use. The development is by the alkaline process.

_Gelatino-bromide of Silver, Emulsion Process._ In this process the use both of the nitrate bath and of collodion are abolished.

The material employed is very troublesome to prepare, and on this account, as well as because of the risk of failure attending the use of home-made articles, it is far preferable it should be purchased. It may be obtained under the name of 'Kennett's Sensitised Pellicle.'