BRUSH DEVELOPMENT The development of negatives, bromide prints and platinum prints by applying a suitable developer by means of a brush instead of immers ing in the developer. For negatives the slower working developers, such as pyro, are more suit able than the rapid kinds, such as rodinal, metol, etc. It is usual to soak the plate in a very weak developer until the image just begins to show, and then to rinse in water and apply the weak developer, or even a normal developer, by means of a camel-hair mop, giving the partially devel oped negative repeated rinses in water in order that there may be no distinct line of demarca tion. Where a sharp line is wanted, glycerine may be mixed with the developer. The brush method enables parts of the negative to be subdued or accentuated in a wonderful manner. The process is perhaps of the greatest service in portrait work where white dresses are likely to give undesired effects. It is more widely used in the United States than in England, and R. W. Phillips, an American, recommends the following method of brush development for por trait work ; a three-solution pyro-soda formula is used : A. Water 20 oz., sodium sulphite oz. ; when dissolved add enough pure acetic acid to turn blue litmus paper red, then add r oz. of pyro. B. Water 16 oz., sodium sulphite 4 oz. C. Water 16 oz., sodium carbonate 4 oz. To make a normal developer add oz. of each of the three solutions to 8 oz. of water. For brush development two working solutions are made up, one the normal developer given above, the other being the same, except that the car bonate is omitted. Then use a separate solution of one-half carbonate and one-half water, or carbonate and one-third water, which ever is found to suit the strength of the negative desired. In the case of a plate exposed on a sitter in white drapery, develop until the image shows faintly, then pour off this regular developer and wash the plate. Next pour on the pyro and
sulphite solution previously made up, hold the negative horizontally up to the light in the hand, and with a camel-hair mop saturated with the carbonate solution rub over that portion of the negative which is to appear the most pro minently. This must be done the first time very quickly, putting the negative back into the solution immediately. The operation is then repeated, the carbonate being well blended over the plate so as not to show streaks and defined lines.
The principle involved is this : the negative is developed only to a slight extent in the first immersion, and as soon as the pyro and sulphite solution is poured on development practically ceases. Then the high lights are controlled absolutely with the carbonate solution. Some little practice is necessary in order to get a per fect result. Over-exposed negatives are unsuit able for brush development, the control being so difficult.
It is found rather difficult to carry out delicate work of this character in the dark-room, and there is a very serious risk of exposing the plate too freely to the light, and so producing fog and loss of quality.
In bromide printing, brush development is very frequently adopted for large prints. A smaller quantity of developing solution can be employed than most workers could use satis factorily in a dish, though the results produced by the brush method are almost always inferior in richness and quality to those obtained in the ordinary manner. The print is thoroughly wetted, so that it will lie perfectly flat on a sheet of glass, and the developing solution brushed rapidly over its entire surface in the manner described under the heading " Brush Toning " Platinotype prints may be developed with a brush if glycerine is mixed with the developer. (See " Platinotype Process.")