526. The plain fixing bath has the disadvantage of becoming dark and discolored when organic developers are used, and consequently, it is liable to stain the plate. This is overcome by using the acid-fixing bath according to the following formula : -

Dissolve, and then add citric acid 11/4 ounces. After this has been dissolved add hypo 16 ounces. When the ingredients are all dissolved the bath is ready for use, and plates should be fixed at least ten minutes after all the free silver or milky appearance has been removed.

527. Life Of The Developing Solutions

Life Of The Developing Solutions. The pyro developer should only be used for one day's developing. The metol - hydroquinone developer can be used repeatedly, so long as it gives good results. You must, however, make due allowance for the fact that each lot of plates is adding bromide to the developer, the bromide being eliminated from the emulsion of the plates previously developed. The developer dissolves the bromide in the plate, and it therefore becomes a part of the solution and will retard the development. This will especially be noticed after the bath has been used for some time, and with short factor developers will tend to materially alter the factor. Carefully watch your negatives and when you find that the developer is acting slow or developing contrasty - in other words, when the bath fails to produce the proper results, make up a new one. Always keep the bath covered, excluding all light, whether in use or not.

528. If you are using a zinc developing tank, carefully rinse it after you are through developing and turn it bottom side up so that it will become dry. A little care will enable you to preserve this tank for years.

529. Practice Work

Practice Work. In preparing the lesson on tank development first provide yourself with a tank holding six 5x7 plates, or their equivalent. Next make a few exposures, which you know to be normally exposed, then prepare enough of the pyro developer to make solution sufficient to fill your tank. If a small tank, twenty - eight ounces will be sufficient. If the developer was made according to formula, you can be certain that the plates will be developed in twenty minutes; but you should prove the accuracy of this and for the benefit of your own experience make a practical test. By watching the plate carefully from the moment it enters the developer, and noting the time of appearance of the strongest light with general outlines slightly visible (which should be thirty seconds), see how near your judgment was right; then, the next step is to examine the plates at the expiration of twenty minutes and see if in your judgment the plate is completely developed. This will supply you excellent practice and will train you in the accurate judgment of the correct development of the plate under all conditions. After each experiment dry the negative and make good solid proof prints, untoned, from the plate, and note the quality of the proofs produced. Make notes on the back of each proof, naming the formula employed, which in this case would be pyro, the time for complete development, and any other data concerning the development of that plate. Note also whether the plate was normal, over or under-exposed. File these proofs in your letter-file for future reference.

530. After trying out the pyro formula prepare the metol-hydroquinone formula, and observe the results in the same manner, making proof prints in every instance, and filing the same with all data connected with the producing of the results. This data will be for your future guidance. After completing your experiments compare the results and judge for yourself which formula you prefer to use regularly; and by this time, if you so desire, you may try altering the formula, which is good practice, and will only have the effect of making you more proficient in your judgment.

If you meet with any failures make use of the Index, and refer to the Difficulty Department, where you will undoubtedly find a prevention or remedy for your difficulty.