In developing great care should be taken to see that no air bubbles remain in the film surface while being developed, as the presence of such will cause spots or marks on the film surface. For the same reason the film surface must be covered as quickly as ever possible with the developing bath, i.e., do not allow one part to be covered appreciably before another. Again all plate or film washing must be thorough and complete, and, above all, if good negatives are desired, it is absolutely necessary to see that no injurious light gets at the sensitive surface until it is finally fixed. For those who prefer to make up their own solutions, the following can be recommended for developing :-

Solution A.

Water, warm ........ ;10 oz.

Soda sulphite (crystals) .... 240 grs.

Pyro ........ ;.... 40 grs.

Metol ............ ;10 grs.

Solution B.

Water ............ ;10 oz.

Soda carbonate ........ ;1 oz.

Potassium bromide .... 4 grs.

Put each solution into separate bottles, and keep well corked. Use the same amount from each bottle, and mix well together. At the above strengths the average time for normal complete development is from two to four minutes. If diluted for economy, the above times will increase.

Another and popular developing bath is made as follows :-

Stock Solution.

Pyro ............ ;1 oz.

Water up to ........ ;6 ozs.

Nitric acid ........20 drops

Add the nitric acid to the water and then add the pyro, the above stock solution will keep for some time.

Pyro Solution. Stock solution .... .... 1 oz.

Water up to ........20 ozs.

This pyro solution will keep for only a short time.

Soda Solution.

Soda crystals .... .... ;2 ozs.

Sodium sulphite........ ;2 ozs.

Potassium bromide .... ;20 grs.

Water up to .... .... ;20 ozs.

Dissolve the above salts in about 15 ozs. of hot water, wait until cold and then add 5 ozs. of cold water; solution will keep for a long time.

For use mix equal amounts of the pyro solution and the soda solution just before they are wanted. If the method of developing by time be not adopted, then proceed to develop until the high lights are quite opaque and all detail is clearly visible. Development is then complete and nothing is to be gained by continuing. Take the plate out of the developing bath and wash well. If the plate image takes a very long time to appear, then the plate, etc., has been underexposed, which fault is most difficult to rectify in that negative, and unless good reasons exist against it, the plate should be scrapped, the prints off it are not likely to satisfy anyone. Should the image come up too quickly then it has been over-exposed, and if detected in time, take it out of the dish and pour over it some of the pyro solution alone. When the development has then either gone far enough, or stopped, put the negative back in the original bath. It is not easy for the beginner to tell when to stop the development, and experience alone will best leach him. After the negative has been well washed it has to be placed in what is termed the fixing solution, which is made up as follows :-

Hypo ........ ;.... 16 ozs.

Water up to ........ ;80 ozs.

The negative must remain in this until the insoluble silver bromide is converted by the hypo (hyposulphite of soda) into silver sodium throsulphate, which is soluble in water, and is dissolved out of the film on the negative. Make sure that the process is finished and complete, this is really important. A stronger solution of hypo may be used if preferred, but it may separate the film edges from the plate (termed frilling), especially if the bath be on the warm side, due to perhaps hot weather. A plate may show signs of frilling after the developing bath, in which case wash it well and place for say 5 minutes in a bath of

Alum .... .... .... 11/2 oz.

Water .... ........ ;20 ozs.

Reverting to the fixed negative, it is now most important to wash it well, go to the extreme, and when washed well, wash it once more. It is imperative that all the hypo be washed out. Allow to dry preferably in a nearly vertical position, say leaning against the wall with the sensitive surface towards the wall, so that dust cannot settle upon it, while wet. Do not dry before the fire etc., the wet gelatine surface is liable to be damaged, and cannot be improved. Judge the resulting negative as to density and contrast and remember that if it be too thin, it was under-exposed, if too dense, then it was overexposed. If flat, i.e., without much contrast, then it was under-developed, and if the contrasts are too much then it is over-developed. Of course, faults in both exposure and development may occur in the same negative.

It is probable that quite a large percentage of photographic printing paper sold is really wasted in trying to get a good picture from a faulty negative, it is much cheaper to scrap such negatives at once, and resist the temptation to spend money and paper upon them. A description of the developing tank of Kodaks Ltd. for films should be of interest, and is as follows :

The " Kodak " developing tank outfit consists of a wooden box fitted with a spool carrier E, a light-proof celluloid apron A, a flanged reel Y, a hollow spindle, two winding cranks C D, a metal tank in which the film is developed, and a hooked rod for removing the film from the solution. See (Fig. 148).

Fig. 148.

A dummy film spool is also provided, with which you should experiment before developing an exposed spool. Using this dummy spool you should work the apparatus with the cover off, until the principle upon which it acts is well understood, and the mechanism is quite familiar.

Everything must be removed from the box and the apron and reel from the metal tank. The winding cranks C and D (Fig. 148) are to be inserted in the holes in the front of the box ; the front is towards you when the spool carrier E at the end of the box is to your right. Pass crank C through the hollow spindle. There is a cross-piece at one end inside the spindle and also inside the hub of the reel. See that this end of both the spindle and the reel is placed at the back of the box. Pass crank d through the hub of the flanged reel Y. Push both the cranks into the bearing-holes on the opposite side of the box.

Attach one end of the apron to the spindle through which crank C passes, by engaging the metal hooks with the lugs on the spindle (Fig. 149). The rubber corrugations must be downward. Turn to the left on crank C, and wind the entire apron upon the spindle, maintaining a slight tension on the | apron by lightly resting one hand upon it.

Film to be used in the " Kodak " Developing Tank must be fastened to the paper at both ends. All films are fastened at one end at our factory. The other end must also be fastened, thus :

Just before you are ready to develop, unroll the spool carefully until about an inch of the gummed sticker is in sight ; moisten the gum sufficiently to soften it and rub it into thorough contact with the spool paper; make sure that it adheres. Wind up the spool again and it is then ready to insert in the transfer box.