The methods of working described for papers apply equally to the same emulsions coated on opal glass.
563. Developers for Bromide Papers. Either of the following developers may be used with advantage.' M etol-hydroquino lie Developer Metol . . . g gr. (1 grin.) Soda sulphite, anhydrous 4 oz. (25 grin.) Hydroquinonc . . . 35 gr. (4 grin.) Soda carbonate, anhydrous 130 gr. (15 grin.) Potassium bromide, x o% solution - • • 45 min- (5 c.c.) Water, to make . . . 20 OZ. (1,000 C.C.) This developer, which keeps well, can be prepared in the form of a stock solution of double strength. This is diluted at the time of using by taking a given quantity of the solution and adding an equal volume of water. 2 When this developer is used at a temperature of about 6° F., the image appears, as a rule, in about 30 seconds, and development is complete in from 2 to 3 minutes.
Amidol Developer— Soda sulphite, anhydrous 1 oz. (25 grin.) Amidol (hydrochloride) 55 gr. (0 gum) Potassium bromide, xo% solution . . . 45 min. (5 c.c.) Water, to make . 20 OZ. (1,000 C.C.) This developer should be prepared at the time of using. At a temperature of 65° F,, the image appears in about 15 seconds, and develop ment is complete in from 2 to 3 minutes.
All the quick-acting developers previously given for the development of negatives, can be used for bromide papers, provided that the proportion of bromide is suitably adjusted.
564. Development. Development is usually controlled by inspection. A number of prints are immersed successively in a dish sufficiently large and with a quantity of developer which will allow of ready handling of the prints. As soon as several prints have been immersed, they should be kept in constant motion. The lowest should be brought to the top, each print in succession, until, the image being correctly developed, the print is transferred to the acid stop bath.
In proportion as fresh prints are developed, the developer becomes charged with increasing quantities of soluble bromide, and especially so as positive emulsions usually contain an excess of potassium bromide. Even if the tem perature of the solution is constant, the speed of development falls off, and the colour of the prints tends to change progressively.
In order to ensure that prints from the same negative are as similar as possible, they should be developed together and for the same time. The beginner, and also the amateur who only prints occasionally, will avoid all uncertainty by exposing and developing a test piece when ever using a new brand of paper or a different type of the make usually employed. This will enable them to ensure correct exposure (§ 553). In order to derive full advantage from this test, it is necessary to ensure that the temperature of the solution is constant, not only as between the test and the development of the print, but equally during the development. This requires that the temperature of the solution should be the same as that of the work-room. Further, the composition of the solution should not be modified progressively, that is to say, fresh developer should be used for each print devel oped separately, or for each batch developed together. Solutions used for developing cost so little that no one should ever hesitate to use a fresh quantity if the finest results are desired.
565. For developing the test piece, the Watkins arithmetical coefficient or " factorial " method may be used with advantage 344), but the " factors " would have to be determined experimentally for this special use. The " fac tors " to be used may be taken as roughly about half those used for negatives with the same developer.
For the two developers given in § 563 the value of the Watkins " factors " for prints on bromide paper are respectively Metol-hydroquinone developer . . A m idol developer . . X If) (B. T. J. Glover, 1921.) The total time of the development of the test piece will be, under these conditions, 5 or re times the interval between pouring on the developer and the appearance of the first details ; and the time of development thus determined should be the same in all cases for the develop ment of prints in the same developer.' 566. Local Control of Development: Brush Development. A worker who combines the qualities of a skilful technician and capable artist can produce excellent results by local development of bromide papers by means of a brush. But such methods are not in any way advisable for beginners.