PHOTOGRAPHY.

Taranaki Daily News, Volume XLVII, Issue 8135, 15 June 1906, Page 4

PHOTOGRAPHY.

Advantage in derclopmci't is nol all on lilt sido of the very energetic lvagent such as metol; indeed, in ordinary cases it is pretty certain tluit a slow develops! - actually gives a better result, and lor this reason there is much importance to be attached to that dual character of the pyrogallic developer, which may ho expressed by saying that die organic constituent alone will nol develop in any degress (a distinguishing point from amidol, hydioquinonc, etc.), nor will the alkaline constituent. Hence it is that the suddenness of an ordinary chemical reaction may be tempered to any extent, and the most perfect control results. Further, a plea may be put in for the slow penetration of the him by the active mixturOj a state of things realised by immersing che plate in the pyro first, and then gradually adding the alkali. The instructions published by Edwards nearlj a quarter of a century ago are recommended by M. Herve, who has spent aiuoh time in the investigation of de/elopers, to those "who wish to work • ; tii certainty and obtain a satisfactory

~i .. , ;vr wide variations in expo jure; titock pyro solution—A: Water, tOU parts; pyrogallic acid, 10 parts, crystallised sulphite of soda, 10 parts; citric acid, 0.8 parts. B: Stock ammonia mixture —Water, 30 parts; strong liquid ammonia, 5 parts; glycerine, 6 parts; potassium bromide. 0.7 parts. To develop, liiut soak the plate for a few seconds in pure water, and remove any air bubbles by means of a brush, and allow it to remain in tlio miter for two minutes, so as to swell the film. Now immerse it in the pyrogallic bath, compounded of one volume of A with from .seven to nine volumes of water, and in •a minute or two pour olf the liquid, add a duo pi'uportiou of the ammonia solution, and return the liquid to the dish. Tho amount of ammonia added and time of development must depend on the behaviour of the plate, but a eonfeuiont quantity may be made with two parti of the stock ammonia solution, di.uted at tho time with fifteon times its volume.of water. Of course, an extra loso of bromide may be u.ed in oase >f quite excessive over-exposure, but jy soaking the film beforehand, as

tbovs recommended, and by the gradual iddition J the compound ammonia -.olution, sufficient control is obtainable in ordinary cases. Tliere should be no difficulty in reducng over-done 'bromide prints; indeed, ).o.p. prints which have been carried too far in the printing can olten be reJucei if treated carefully. The familial 'Fanner's" reducer, consisting ol hypo and ferri-cyanidc, is apt to attics the delicate detail i)i tlie lightei .ones before the shadows, thus destroying tha range of light and shade, For this reason a mollification was suggested jy nil' A. Haddou, accx-ruing to u iiom a it) per cent, solutiuii ol aininoniuiij sulphocyanide and of potassium fcrrijyanide are first maue, ami tnen 10U jrops of -the former and ten drops of the .atter aro taken with loz of water. This reducer makes but i'ttle alteration in olio tono of the print, but it has the (lis. advantage of acting on the gelatine somewhat, in virtue oi the ol olio sulphocyanide employed; thereioiv [t is sometimes advisame co Harden in lormalin previously to us;)ig. Potassium bichromate ana hypo is of use hi >onie cases, though t»io I'wUitw- arc 1101 very pleasing, it should be. used Ui: follows: Of a 0 per ceiu. bichromate solution, 15 drops; hypo, Joz; water, lOoz. Ammonium p*i'£iiipiiatc when osed in a 3' per oent. «u.<uh>ii is a steady and useful ru-ieay. Vei\ thorough washing must in tim< case Ik given both before and alter its use. or do these exhaust the number of re ducers for prints. Potassium cyaimL by itself or in conjunction w.th-iodm-liavo both been recommended,-bill 'their action is often too rapid- to be under control, besides the natural objection which may exist to employing so deadly a poison. Two other formulae remain. The first is uranium nitrate, which acts evenly provided the hypo it sufficiently strong to prevent the uranium from staining. A 1 per cent, solution of the salt is used; five ounces oi hypo, aro dissolved in ten ounces of hot water. Of these we take Hypo solution, 50 drops, and uranium Milution. loz. Finally, mention should bii made of another reducer —cupro-ammonhiin and hypo. (A) Ten grains of suiphaie u. copper aro dissolved in ten ounces ol water, and to this ammonia is added, till the solution becomes clear blue; (11) then fifty grains of hypo are dissolved in ten ounces of water, ■ and tha Uvu solutions are to be mixed in 'Vj-.ia! parts. Simple as tlie platinotype process is. and uniform as are the results, then are many who hesitate to adopt it because of its possessing a certain quality of finality—a print overdone is perhaps less amenablo to after treatment than the case of a print in silver. It is practically impassible to reduce an overprinted platinum imago, but if under printed it can be intensified,, although obviously the additional image is not platiuni, but silver. A few drops of eilvor nitrate solution are added to a solution of : Pyrogallic acid, 2gr; citric acid, 20gr; water, loz. Or hydroquinone in the same proportion may be substituted for pyro. The print is placed in this solution, and rocked until the desired depth is arrived at, when it is well washed and fixed in hyposulphite of soda, as with an ordinary silver print, and finally Trashed again.