PHOTOGRAPHY.

Auckland Star, Volume XLII, Issue 299, 16 December 1911, Page 15

PHOTOGRAPHY.

THE PERCENTAGE SOLUTION. Many photographers seem to think that there is some special virtue or advantage in percentage solutions, so that at times a formula is published in a very roundabout way. The following formula, which was published a few days ago, is a typical example. First we are told to make three 10 per cent solutions of salts, A. B, and 0. We now take 2oz of A, loz of B, and loz of C, and add 6oz- of water to make lOoz all told. For all such practical purposes we may reckon the ounce (of solids) as 440gr, so that loz of 10 per cent contains 44gr. We thus have BSgr of A, 44 of B, and 44 of C ; n lOoz of water. This last sentence gives us all we need know, and is in many cases a far more convenient way of giving a formula.

BLEMISHES ON ALL NEGATIVES. This Ls essentia..,, -e day of the small negative, made with a view to subsequent enlarging; consequently, the presence of defects in these small negatives is a very frequent source of anxiety and queries. One of our chief, because most frequent, troubles is the minute clear pinhole like round spot with sharply denned edges, caused by a speck of opaque dust adhering to the film, andSeo preventing the light affecting this particular part of the film so that it fixes out as a little circle of clear gelatine on the glass. If the spot is fairly large, one can often tone it out on the fißm side with a little Indian ink or lamp-black (water-colours), using either a finely-pointed small camel's-hair brush, or, what is easier. Viz., a mapping pen. If the spot is very small it is not very likely to show at all on the enlargement. It should be noted that a rough, or even matt, surface is not nearly so likely to -show pinhole spots as is a smooth or glossy surface.

DIRT IN SOLUTIONS. The cause of numerous defects 5n both plates and papers may often be, accounted for by dirt in solutions. There is always an accumulation of dirt in solutions which is inclined to settle on the surface of the film, and which is frequently omitted to be removed. The surface should be carefully swabbed with a tuft of absorbent cotton wool after each process of developing, fixing and washing. The final swab is especially useful, as it not only cleanses the surface but removes all surface water. The cotton wool wetted in clean water and pressed nearly dry will not be in any way harmful to the surface. In the drying every care must be taken to avoid dust settling on the film side of the negatives, as pinholes and other defects are caused in this manner. Frequently such defects arc credited to the quality of plates and dust in plate carriers, etc., whereas they may often be caused by dust setting during the process of development.

TANK DEVELOPMENT. Stand or tank development is so popular just now that no excuse is needed for referring to this subject again, in order that I may quote a formula which is given by Mr. H. B. Ward in this week's issue of the "AJ > ." The writer communicates a useful and suggestive article on this method of dealing with lanternslides, and commends the following for sepia or cool brown colours: (A) Pyro 20gr, potass metabisulphite 60gr, potass bromide 20gr, water 30oz. (B) Ammonia (.880) ldrm, water 30oz. A and B combined (i.e., 60oz) suffice for thirty slides in ten-twelve minutes, with Paget slow lantern plates and 3in of magnesium ribbon burnt at 4ft. For warm brown to red colours burn sin of ribbon at Ift, and use ; the following developer: (A) Pyro 30gr, potass metabisulphite 30gr, water 30oz. (B) Ammonia (.880) ldrm, water 30oz. (C) Ammonia bromide loz, ammonium carbonate loz, water lOoz. For warm brown colours combine A and B and add 3oz of solution C. The time required is ten to fifteen minutes. For still warmer, i.e., more red, colours Soz of C solution may be used. For workers who use other brands of plates it will be advisable to make one or two trial exposures with a couple of average or fairly representative negatives before making a big batch of exposures, i