Positives Direct

POSITIVES. DIRECT The simplest method of obtaining a direct positive upon a dry plate is to expose (avoiding over-exposure) and develop in the usual way, but not fix. After washing, immerse in Potassium perman ganate . . . 5 grs. I g.

Sulphuric acid . 10 mills. 2 ccs.

Water . . . to oz. I,000 „ until the image disappears. Next soak in a weak solution of oxalic acid (4 grs. per ounce, or about t g. per too ccs.) until the brown stain is cleared from the gelatine. The plate is then well washed, exposed to actinic light, again developed, fixed in " hypo," and washed. For the re-development the following is excellent :— Metol . . . 5o grs. I x•5 g.

Sodium sulphite . too „ ,, Caustic soda . so „ irs „ Water . . . to oz. x,000 ccs.

The permanganate reversing (or reducing) bath may be replaced by a 5 per cent. solution of ammonium persulphate with 5 per cent. of alum, the weak oxalic bath being omitted.

Major-General Waterhouse recommends re ducing the exposure to one-thirtieth of the normal, developing and fixing as usual, but using the following developer : Lithium carbonate . so grs. g.

Sodium sulphite . so „ I Eikonogen . . 5o „ „ Thiocarbamide (saturated solution) . . Pew dropsWater . . . to oz. I,000 ccs.

Another method suitable for very slow plates is to expose, develop until the image is seen on the glass side, wash, and immerse in— Potassium bromide . 50o grs. I15 g.

Iodine . . . too „ ,, Water . . . 10 oz. I,000 ccs.

until the image is bleached. Then wash, develop with any developer in strong daylight, wash and fix.

Lantern Slides and Bromide Paper.—The above methods may be used, but the late Douglas Carnegie worked out what is considered to be a more certain process. The lantern plate or other slow plate should be backed ; it is ex posed (avoiding over-exposure), developed with metal - hydroquinone, washed, and immersed for about two minutes in the following re versing bath, which, in hot weather, needs to be diluted : Potassium bichromate 75 grs. 17 g.

Nitric acid (pure) . 45 mins. 9 ccs.

Water . . . to oz. I,000 „ After bleaching in this bath for a moment only, replace in the developer, rock the dish for about 3o seconds, and then, while still in the developer, expose to light, for say 20 or 3o seconds, at a distance of I ft. from an ordinary No. 4 burner. The second development must not be pushed to the point of fogging the background. Fix in an acid fixing bath. Bromide prints may be obtained direct in the camera in the same way, using " glossy " paper ; a weaker light (equal to one candle) is placed 2+ ft. distant from the print lying in the dish, and allowed to act until the edges of the paper protected by the rebate begin to darken. The colour is not very pleasing and should be modified by toning, sulphide being preferable.

Balagny recommends developing a plate with acid-amidol (see " Amidol, or Diamido phenol "), washing thoroughly, exposing for 3o to 45 seconds to diffused daylight, and then immersing (in the dark-room) in Potass. bichromate . 15o grs. 35 g.

Nitric acid . . 6o mins. 13 ccs.

Water . . . to OZ. 1,000 „ This converts the image into silver chromate, which is dissolved out by a TO per cent. solution of sodium sulphite plus 3 per cent. of acid bisulphite. The plate is next well washed, when nothing remains but the exposed silver haloids, which are developed with add amidol minus the bromide.