Over-Exposure

If a plate is suspected of being overexposed 10 drops of bromide should be added to each ounce of the developer before it is poured over the plate; and if the image flashes out quickly the solution must be returned to the measure, and a further quantity added. Some workers, on finding after commencing development that the image flashes out at once instead of gradually, and is therefore over-exposed, remove the plate at once into a weak solution of ammonium citrate (5 grs. to the ounce), and after about a minute wash and replace in the developer. Others wash the plate under the tap, and replace in the developer to which three times the amount of bromide has been meanwhile added. Unless the over-exposure is very serious it need not occasion anxiety, as the resulting negative will print well enough after treatment in a reducing bath. The great mistake of beginners is to under-develop over-exposed negatives.

When Development Is Complete

Most classes of plates may be allowed to continue in the developer until the lines of the image are plainly visible on the glass side; but with some thickly coated plates the image never penetrates completely through the film. Another test is the commencement of "fog" on the white margin left by the rebate of the dark slide. When held up against the ruby lamp the sky and other portions which are to appear white in the resulting print should be approaching a solid black, and the details in the shadows well marked.

Factor For Timing Development

Mr. Alfred Watkins, the inventor of many valuable instruments for securing exactitude in exposure and development, has prepared a table showing the factor necessary to calculate the time when development reaches a degree found by trial to give a sufficient amount of contrast. To use the table, multiply the time which elapses between the immersion of the plate and the first appearance of the image. Thus, if the image when we are using a pyro developer 5 grs. to the ounce appears in 45 secs., development should be complete in just under 5 minutes.

Factor.

Adurol...............

5

Amidol (2 gr. per oz.)...........

18

Diamidophenol........

60

Diogen .............

12

Edinol...........

20

Eikonogen ...............

9

Glycin (carb. soda) ..............

8

Hydroquinone..................

4 1/2 to 5 1

Pyro Soda (1 gr. to oz.).....

9 to 18 2

„ (4 gr. to oz.).....

4, 82

,. (5 gr- to oz.).....

31/4. 6 1/23

Imogen Sulphite......

6

Kachin........

10

Metol........

30

Metol Hydroquinone.....

14

Ortol.......

10

Pyrocatechin.......

10

Quinomet......................

30

Rodinal................

40

Controlling Development

We have seen that the restrainer increases contrast; we can diminish contrast by diluting the developer. Dilution renders the action slower, and incidentally gives the ehance for more detail to appear in the shadows before the high lights have become too dense, and so a softer negative can be obtained. With the normal solutions, if a plate is removed from the developer before the usual time, the contrasts will be very great, and the prints show only ghostly high lights; longer development improves the shadows and gradations; very long development still further levels matters, till in the end the shadows are so filled up that printing becomes well-nigh impossible.

1 The latter figure with minimum amount of Bromide.

2 The latter figure without Bromide.

Temperature

The normal temperature for solutions is 650 Fahr. In hot weather developers should be used much weaker than the usual strength, and in cold weather some means of keeping the dark room warm is very desirable. Some developers - quinol and ortol especially - will work very slowly at a low temperature, and at 55° action practically ceases. But it is a mistake to warm the developer unless the fixing bath and washing water can also be raised to the same temperature.

Fixing Bath

When development is adjudged complete the plate should be washed in three changes of water, and may then (except in hot weather, or when the gelatine edges show much frilling) be transferred direct to the fixing bath consisting of hyposulphite of soda and water in the proportions of 4 ozs. to the pint. It is an old-fashioned practice to add a few drops of ammonia to the hypo bath. After 5 minutes' immersion in the hypo bath the negative may generally be examined by daylight without serious injury, but fixation will not be complete for at least 10 minutes, or about 3 minutes after all traces of the white bromide of silver have disappeared at the back of the film. The same hypo solution can be used again and again for fixing plates until it becomes discoloured or fixes too slowly; the bottom of the dish must be frequently sponged to remove the black precipitate which collects there. Large firms and clubs collect their stale hypo in a barrel, the contents of which are periodically evaporated, and the residues sent to a refiner, who recovers the silver.

Acid Fixing Bath

Many workers prefer to the above alkaline bath Prof. Eder's acid bath, which is considered to give greater clearness and brightness. Mix tartaric acid solution (1 to 2) 3/8 oz. with sodium sulphite solution (1 to 4) l 1/4 oz., and then add the mixture to each pint of the ordinary hypo bath. Another very good one is made by adding 1/2 oz. of potassium metabisulphite to each pint of hypo solution.

Washing The Negative

On removal from the fixing bath the plate is well rinsed under a tap or in several changes of water, and must then lie either in a washing tank or in running water for several hours to remove the last traces of hypo from the film. Hypo left in the film will not only lead to spots, stains, and premature fading of the negative, but may injuriously affect the printing papers placed in contact with it. Or, after an hour's washing, it may be placed in a clearing solution consisting of alum I oz., citric acid 1/2 oz. (or nitric acid 20 drops), water 10 oz. Five minutes will suffice for this before a final washing under a tap, when the plate may be put away in a rack or some other secure place to dry.