Messrs. Lumiere have urged that if the alkaline salts of the tribasic acids, as for instance the phosphates of soda and potash, were employed as accelerators, the danger of stains occurring would be greatly diminished.
Paramidophenol developer is very widely employed under the name of Rodinal, a proprietary article said to consist of a solution of paramidophenol hydrochlorate with sulphite of soda, to which sufficient of a caustic alkali has been added to redissolve the precipitate at first formed. The concentrated solution is cheap, keeps well, and produces a developing agent of considerable range, but slow in acquiring density. The image appears more quickly than with pyro, and details are distinguishable almost at once, but development is not complete for a con siderable time. For ordinary use take Rodinal . . . . . . . i part Water . . . . . 30 parts For under-exposures or greater detail add more water ; to increase contrast strengthen developer. Bromide acts as a mild restrainer, and may be freely added. The hydrochlorate is generally the salt of paramidophenol con sists of needle crystals which easily turn a dark colour, but this does not materially affect development. A good stock solution is Paramidophenol . . . . . . 6o gr.
Sodium Carbonate . . . . . . . . 2 oz.
Sodium Sulphite . . . . . . 2 oz.
Water . . . . . . . . . . 20 oz.
Dilute with from 3 to 5 times the bulk of water before using.
Metol is a very powerful and energetic developer, producing density very rapidly, and bringing up detail in the shadows almost simultaneously with the high lights. Softer results are obtained for short exposures than with most other. Unfortunately it produces a very painful affection of the skin. Rubber gloves should be used, and the fingers washed immediately after develop ment. The usual formula is : A. Metol 1. . . . . . f oz.
Sodium Sulphite . . . . . . . . z Water . . . . . . . 25 B. Sodium Carbonate Water . . . . . . . . zo Metol is generally preferable as an addition to hydro quinone or pyro, when it acts as a useful corrective. For an example we will give the Imperial Dry Plate Company's developer of this class (single solution) : Metol . . . . . . . . 5o gr.
Hydroquinone . . . . . . . 40 Sodium Sulphite . . . . . . soo Jot Potassium Bromide . . . . . . 25 Sodium Carbonate . . . . 500 8 2.
. . . . . . . 20 oz. ..5" Or for two solutions (Metol Pyro) : A. Metol . . . . . . . 45 gr.
Potass. Metabisulphite . . . . . Ito . . . 55 ,, Potass. Bromide . . . . . zo Water 20 oz Sodium Carbonate . . . . . . 4 oz.
. . . . . . zo Hydroquinone from this de veloper tend to rather harsh contrasts, detail in the shadows not appearing until the high lights have acquired considerable thickness. Its chief value, especially in solutions with bromide, is for the necessary contrasts when copying prints and drawings, and for some of the photo-engraving processes. When hard negatives are desired, try : A. Hydroquinone . . . . . . . . 4o gr.
Metabisulphtte of Potash . . . . . 40 I3romide of Potassium . . 5 nWater . . . . . . . . . to oz.
B. Caustic Potash . . . . . . . . too gr.
Water . . . . . . . . to oz.
Amidol developer is slightly acid in solution and acts very energetically without any alkali. The image appears almost at once in full detail, but requires long development. It produces good black negatives, and is often recommended for instantaneous work. Amidol does not keep well in solution but a stock solution consisting of Amidol . . . . 8o gr.
Sodium Sulphite . . . . . . 800 Water . . . . . . . . 8 oz.
will keep for a few weeks if well corked. For use dilute t part with 4 parts of water. Old amidol developer sometimes leaves serious stains behind it. The best way of all is to make a stock solution of Sodium Sulphite . . . . . t oz.
Potassium Metabisulphite . . . . 8 IP Water . . . . . . 20 and with a horn spoon measure out 5 gr. of dry amidol for every two ounces immediately before using. A very weak solution of citric or acetic acid is a better restrainer for this developer than bromide of potassium.
Diamia'ophend F1,0 variation of that previously described, as Nvi 1 1 be seen by the symbol. It will give an excellent black image with good gradations, and is not so likely as amidol to produce stains, but it does sometimes cause inflammation on delicate skins.