Yellow Screens for Orthochromatic Plates. For general landscape work fix an ordinary lantern plate, wash and dry it, and then soak it for one minute in •—
Napthol yellow dye Water.
Rinse it in clean water, and dry.
Methylated spirit Water Formalin .
A solution Hydrofluoric acid.
Cut through the film of the negative all round about 1/8 inch and place on a flat bench, and pour on to it just enough of B to cover it, letting it remain until the film appears quite loose; remove the strips all round. Now pour on about 1/2 ounce of A solution and gently spread all over ; lay a piece of clean white paper on negative and gently squeeze down. The paper can now be carefully removed; carry the film with it. Now place the paper film side up on to a piece of glass and pour on another 1/2 ounce of A solution, and squeeze another piece of paper on to it. Now remove the first paper by gently pulling it, when the film will be left on the second paper. Now pour again on to the film another 1/2 ounce of A solution, and place the film side down on to a piece of clean glass, and squeeze well and carefully. Now raise one corner of the paper and gently pull it off, leaving the film on the glass, but reversed for carbon printing.
The following approved formula;, gathered from various sources, are here given, that the reader may have them ready for reference:—
Sodium hyposulphite ... 4 ounces Sodium sulphite 1 ounce.
When dissolved add 30 drops of sulphuric acid. If preferred, citric acid may be substituted for sulphuric, in which case dissolve 1/4 ounce citric acid in 4 ounces water and add the whole to the solution of hypo and sodium sulphite. For bromide paper dilute the above with 24 ounces of water.
In some circumstances, as, for instance, in warm weather, it may be convenient to combine hardening effect with the fixing-bath. The simplest formula is as follows:— Common alum ..... 1 ounce Water......40 ounces.
When dissolved, add—
Sodium sulphite .... 1 ounce.
When this is dissolved, add —
Sodium hyposulphite ... 8 ounces.
For bromide paper dilute the above with 40 ounces water. Barnet Alum Hardening-bath for Plates and Papers.
Alum ...... I ounce.
Water ...... 20 ounces.
Soak and well wash negative or print for ten minutes.
Gum sandarac .... 2 ounces.
Gum benzoin f ounce.
Oil of lavender . . . . ^ »>
Methylated spirit .... 20 ounces.
When dissolved, filter. The negative is to be warmed before applying the varnish and then heated strongly.
Orange shellac ..... 2 ounces Sandarac ..... 2 ,,
Canada balsam ..... 60 grains Oil of lavender ..... 1 ounce.
Methylated spirit .... 16 ounces.
To be used cold, the plate being also cold. The varnish must dry naturally without heat.
The ordinary " japanner's gold size " diluted with refined benzine may also be used as a cold negative varnish.
A formula giving an exceedingly fine grain is as follows :—
Sandarac (finest white) 2| ounces.
Mastic „ ,, ... -| ounce.
Ether (spec. grav. 725) . . .25 ounces Benzole ..... 14
First mix the ether and benzole and shake well, next add the two gums. When all is dissolved, filter; now add— Methylated chloroform ... 1 ounce.
The quantity of the latter may be slightly increased if an excessively fine matt grain is required.
Celluloid being soluble in strong spirit, a varnish for these must be made with strong or undiluted spirit, and must not when dry be too brittle, or when the film bends the varnish will crack. The following is recommended and can be used equally well for ordinary negatives on glass:—
White hard varnish .... 10 ounces Liq. ammonia -88o .... (seebelow) Water......5 ounces.
Only sufficient ammonia should be added to just dissolve the precipitate first formed.
There are two groups of chemical restrainers in common use—bromides and citrates ; the former are more generally employed, potassium bromide being the favourite, and a 10 per cent, solution thereof should be in every dark room.
Bromides of potassium, ammonium, or sodium may be used, but they all differ relatively in their restraining power. Thus, 98 parts of ammonium bromide are equal to 119 parts of potassium bromide, or 103 parts of sodium bromide.
The effect of the bromides is to prevent excessive density being gained in the high-lights before detail has developed in the shadows or less exposed parts.
The effect of the citrates is to check the production of detail, but to allow density to increase, and they are hence especially valuable in cases of excessive over-exposure.
The citrate of potassium, ammonium, or sodium may be obtained from the chemist, and a 1 to 10 solution should be made for use, a small quantity being added to the developer according to requirements, beginning with about two drops to the ounce.
Should a negative develop abundance of detail but refuse to increase in density, the citrate solution may be added, and the plate left in the developer for hours if necessary without its "fogging".
A negative which for any reason is too thin and of too uniform a tint, giving a flat print lacking contrast and relief, is subjected to one or other of the numerous processes for intensification.
The usual method is that in which the plate is first bleached with mercury bichloride, and then treated with a reagent, which reconverts the image, blackening it and increasing its density.
Full particulars of this are given elsewhere, and it is only necessary to here add that the increased relative density of the various tones differs according to the blackening reagent employed.
According to some recently published results, the least degree of alteration is produced by potassium hydrate and the greatest by Schlippe's salt.
The plate having been bleached in bichloride of mercury, the degree of ultimate intensification secured by using the undermentioned reagents is in the order of the following list, commencing with the least powerful :—
1. Potassium hydrate (caustic potash), 2 per cent, solution.
2. Lime water.
3. Sodium sulphate, 10 per cent, solution.
4. Ammonia "880, 20 drops to 1 ounce water.
5. Silver cyanide (silver nitrate and potassium cyanide).
6. Ammonium sulphide (1 part strong solution in 10 parts water).
7. Schlippe's salt.
This last named giving the maximum degree of intensification, it may be useful in the case of exceedingly thin negatives. The formula is :—
Schlippe's salt (sodium sulph.-antimoniate).....3 ,,
Liquid ammonia ..... i part.
The bleached negative, alter thorough washing, is immersed in the above and finally washed.
Instead of hydrochloric acid in the mercuric chloride solution many workers prefer ammonium chloride :—
Mercuric chloride .... 5 parts Ammonium chloride . . . . 5 ,, Water.......100 ,,
Immersion for a few minutes in a bath composed of 1 ounce common table salt in 2 ounces water, or 1 ounce ammonium chloride in 10 ounces water, after bleaching and before blackening, often leads to more brilliant results.
When dissolved, add :—
Hydrochloric acid . . 50 to 100 drops
(Or I ounce citric acid may be substituted for the hydrochloric acid)
This should remove the yellow or brown stain or discolouration which is often found after fixing a pyro-developed negative.
Bright metallic spots and brown or black ones due to silver may be removed by immersing the plate in a solution of iodine in methylated spirits. Just sufficient should be added to produce a solution of medium sherry colour. Or the following formula may be preferred :—
Potassium iodide ..... 1 part.
Iodine (metal) sufficient to make a solution the colour of brown sherry.
To remove such a stain as this the simple alum and hydrochloric clearing-bath may serve, but if not, then wash well and immerse in a 10 per cent, solution of sodium sulphite and finally wash thoroughly.
A universal mountant is made as follows :—A teaspoon-ful of fine powdered Glenfield starch is made with very little cold water into a smooth thick batter; next pour in a very fine slow stream of boiling or very hot water—say, from a kettle—stirring incessantly meanwhile; presently the whole will become gelatinous, and when just so thick as to admit of the spoon standing up in it remove the whole to a cool place. When cold, the starch will be a thick jelly, and it is used in this form by first wetting with cold water the mounting brush and then applying it to the jelly-like mass, as one does with a pan of moist water-colours. This will be sufficient to spread on the back of the print. A pinch of powdered alum may be added whilst stirring. This mountant must only be used whilst fresh, and destroyed when it turns sour.
Soft gelatine.....200 grains.
Soak in 6 ounces distilled water for one hour; dissolve this by means of a water-bath or other evenly distributed heat, and add, a little at a time, 2\ ounces methylated spirit, stirring constantly. Allow to cool and set. Should any spirit separate out, remelt and add a little more water.
We shall now have a thick, white, firm jelly, which must be heated to a condition of solubility and so used.
Should this mountant prove too thin, the amount of gelatine may be increased from 200 to 300 grains.