Another formula which is used by several photographers for landscape work is ; Ferrous sulphate zo grains Copper sulphate to grains Acetic acid (glacial) 15.20 minims Alcohol quant. suf.
Water ounce This will give very clear and brilliant images, and the exposure is said to be shortened. A formula for a developer giving very intense images is the following : Protosulphate of iron 36 grammes Sulphate of copper grammes Water 1000 C.C.
Glacial acetic acid, 85 per cent so C.C.
Alcohol 40 c.c.
The addition of many organic substances to the developer has been recommended. Gela tine, sugar, glycerine and collocine, if added to the developer, cause the silver to deposit much slower, and greater density is obtained. A developer containing an " organifier," as it is termed, is made up as follows: Ferrous sulphate zo grains Acetic acid (glacial) to to 15 minims Lump sugar to grains Alcohol quant suf.
Water t ounce Developing the Image.—The plate is removed from the dark slide, and held over the sink either by one corner or preferably with a phneumatic plate-holder. The developing solution is placed in a developing clip, and a sufficient quantity of it to well cover the plate is swept over in one wave, entirely covering it in one operation, but if possible without spilling the solution. Practice alone will enable the operator to do this successfully. The developing solution is kept moving over the plate for twenty or thirty seconds, when it is either thrown away or transferred to the residue jar. If the image flashes up quickly, and is of an even gray, the exposure has been too great, and if, on the contrary, it comes up tardily, or in black and white patches, the exposure has been too short. This is, of course, supposing that all the previous operations have been correctly carried out.
If development has not been carried out far enough the plate can be washed under the tap, and a fresh supply of developer applied. If a small quantity (ten drops to each ounce of developer) of a ten per cent. solution of silver nitrate, acidified with nitric acid, be added, it will give considerable increase in both detail and density. This is termed re-development, and should only be practised if the image, after the first application of the developer, is weak and wanting in detail. If, however, it be weak, and yet full of detail, intensification is necessary.
plate is, after development, washed and fixed by pouring on— Potassium cyanide , 25 grains Water i ounce Or— Sodium hyposulphate too grains Water i ounce In one of these solutions the plate must remain until the yellowness disappears entirely from the plate. If potassium cyanide be used as a fixing agent it should be remembered that it is a violent poison ; even its fumes dangerously affect some persons.
After fixing, the plate is well washed in water.
Intensifying the the plates are wanting in density the image must be intensified. The plate is taken on a pneumatic holder and flooded with
Pyrogallic acid a grains Citric acid 2-4 grains Water i ounce Or— Ferrous sulphate 6 grains Citric acid 12 grains Water 1 ounce The pyro intensifier brings up the image much quicker than the iron, which is suitable for a picture that has been properly exposed.
Another method of intensifying collodion wet plates is with an alkaline solution of silver. This method was first pointed out by Abney in 1874, and worked out later by Mr. Farmer. The following is a description of the method : Silver nitrate 1 ounce Water 12 ounces Potassium bromide f ounce Water 2 ounces Sodium hyposulphite 2 ounces Water 6 ounces Add solution B to A, and after washing the precipitated bromide thoroughly by decantation, dissolve it with agitation in C. The liquid will at once become muddy, when it should be either filtered clear, or allowed to stand for a day or two and the clear part filtered off. It is then made up with water to sixteen ounces and kept ready for use. Other intensifiers are given under that heading. Intensifying may be done either before or after fixing. If the image is clear and free from fog, intensification is best accomplished before fixing, but if the plate has been over-exposed it is best done after fixing, as before fixing it acts as a developer and would produce fog.
After intensification and fixing the plate is thoroughly washed and dried. If dried quickly by the application of heat the density of the negative will be slightly increased. When dry the plate is ready to be varnished.
collodion film being very delicate and easily scratched it is necessary to give it some hard protective coating. This is usually a resin dissolved in spirit. This varnish may either be purchased ready for use, or it can be manufactured by dissolving one pound of seed lac in a gallon of methylated spirits. It will require keeping several days in a warm place before it is all dissolved. It must also be well shaken every now and then. When it is quite dissolved the solution is decantered off and filtered. Other methods of making varnish will be found described under that heading.
To coat the plate with varnish heat the former to a blood heat, and apply the varnish in the same manner as described for coating the plate with the collodion. When the superfluous varnish is drained off into another bottle rest the lower edge of the plate upon blotting paper to remove any drops of the varnish. The plate is then heated till the back becomes uncomfortably hot. A good method of heating the plate is by moving it briskly over a lamp chimney or a Bunsen burner. It must not, however, be placed near enough for the solvent of the varnish to catch fire. If amber varnish be used it must be applied cold.
The negative is then ready for the printing operations.