495. A pyro bath can be used continually during one day, so long as it produces proper results, and develops in the given time; usually a twenty-minute bath of ninety-six-ounce solution will develop twenty-four 5 x 7 plates before showing signs of weakening. A pyro bath should never be strengthened when it becomes weak but replaced by a fresh bath.

496. The metol - hydroquinone developer can be used continuously for days, for with these agents the action is continuous for a considerable length of time, and only needs renewing when the bath ceases to produce the proper strength, and quality in the given time.

497. The required time for development for either pyro, or metol, is greatly governed by the temperature of the developer, and where the factorial methods are employed the temperature is of the utmost importance. For example: If it requires twenty minutes with the pyro formula to fully develop a plate with the temperature of the developer at sixty - five degrees, it would probably take forty minutes if the temperature were forty-five degrees. This change of temperature changes the time of development, for the warmer the bath the quicker the development is completed, and the colder the bath the slower would be the action of the developer.

498. Caution. It is not advisable to depend entirely upon the normal time for developing, especially where all classes of exposures are developed at once, for after a bath is used for some time it is liable to work a trifle slower, but there is one thing you can be certain of, no plate, whether under or over-timed, will be completely developed in less time than those of normal exposures. Therefore, your developer being prepared for a normal exposure, plates of all classes can be placed in the bath at the same time, and when the time for the proper developing of a normal exposed plate is up, all plates can be removed from the bath and examined one at a time, and if any of them lack the required strength, or are not completely developed, place them back into the tank for further development, and examine again from time to time, and as each plate reaches the proper strength remove to the hypo bath.

499. Bear in mind too that the best negatives are obtained from fully-timed plates, and that you should also endeavor to make all your exposures as even as possible, for where the exposures are very near the same the development will be more accurate. Slow development with pyro is preferable to quick development, as the addition of water to a pyro developer produces finer grained negatives, and the detail and gradation in the highlights and shadows are better.

500. In tank development the plates are placed in a vertical position. This accounts for the fact that the developer accomplishes a quicker and more even action. By this we do not mean that it develops quicker, but the action of development sets in quicker, and more evenly than if the plates were placed in a horizontal position; and it, of course, also overcomes the necessity of rocking the trays or agitating the developer, for this agitation of the developer, unless done gently, causes harshness and a coarse grain. The tank developing is uniformly even, without a tendency to double the tones, producing negatives that are clear, with fine highlights and remarkably fine grain.

501. If you are in the habit of developing a large number of plates at a time, you will find a developing tank or stand method a great time saver, for after loading the tank and taking the time, you can be working at something else until the plates are ready for fixing. In order to make certain that you do not forget the time, an ordinary alarm clock can be brought into use by simply setting the alarm at the time plates should be developed. When the alarm rings take out the plates and place them in the fixing bath, and if you have more plates to develop fill up the tank and again set the alarm. Where a large amount of developing is done more than one tank can be used.

502. The principal requirements for successful developing with the tank method is to ascertain the proper strength of the developer, which will develop the plates completely in a certain length of time. This can only be obtained accurately by the factorial method, as explained in previous instruction, always bearing in mind that the time of appearance is also governed by the temperature of the developer. The temperature, therefore, should be as uniform as possible.

503. We give below two formulae, the pyro is a twenty-minute developer, and the metol - hydroquinone will develop in twelve minutes, which time, however, can be shortened or lengthened by strengthening or reducing the developing solution. The stock solution prepared for this pyro formula is exactly the same as that given in formula for universal developer, and the same proportions are used, only we dilute the solution twice that of the normal bath. That is, we add three times as much water as we have bulk of solution in the normal bath.

504. Formula For Developer. - Pyro Stock Solution No. 1

Water.....................

6 ounces

Sulphuric Acid............

................ 1 dram.

Pyro......................

................ 1 ounce.

Stock Solution No. 2

In a 36-oz. bottle pour 2 ozs. Stock Solution No. 1, and add thereto 32 ozs. water.

Stock Solution No. 3.

Sulphite of Soda ( Anhydrous ), 40 hydrometer test, or if by weight,

Sulphite of Soda (Anhydrous).

........... 1 ounce.

Water.........................

13 ounces

If crystal sodas are used it will be necessary to use two ounces, as anhydrous is twice as strong as the crystals.

For uniform results we would advise that the solutions be prepared by hydrometer test..

Stock Solution, No. 4

Carbonate of Soda, 20 hydrometer test, or if by weight,

Carbonate of Soda (Anhydrous)..

1 ounces

Water..........................

23 ounces

If crystal sodas are used, two ounces of carbonate will be necessary. We would advise that this solution also be prepared by hydrometer test.