Typical amidol formula for tray development from Edmund W. Lowe.

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These developers should be made up just before use, but can be kept for a few days in full, tightly closed bottles if necessary. The keeping qualities are greatly increased if a solution containing ½ gram of stannous chloride and an equal amount of tartaric acid in 10 cubic centimeters of water is added to each liter of developer. A few pieces of bright mossy tin should he then dropped into the solution.

An amidol developer preserved by this method can be used over and over until it is exhausted. Even then it need not be thrown away, for the spent developer acts as a densitizer. To use it as such, the spent developer is diluted with 5 volumes of water and the plate or film immersed in it for 5 minutes in complete darkness. Then the film is placed in fresh amidol developer and developed under a yellow safe-light where the appearance of the image can easily be watched and controlled.

Formula B should he used on negatives that are known to be correctly exposed. Developing times are 3 to 8 minutes at 18.5°C. If there is doubt as to whether negatives are under or over-exposed, development may be started in Formula C and if the highlights tend to become dense before shadow detail appears, the negative should he immediately removed and placed in a dish of water. The dish is rocked two or three times and then left undisturbed. If the negative does not develop completely in the water hath, it may then be finished up in Formula A.