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150 THE PHOTOGRAPHIC NEWS. [February 20, 1891. Angeli, from whose brush there exists a portrait of Queen Victoria, which, on the occasion of her jubilee, was reproduced in colours by the Illustrated London News. In the brotherly co-operation of painters and photographers there lies a great success, for the latter have long con sidered themselves artists, for which the public oftenlaughed at them. But now a photographic exhibition is to be judged of from an artistic standpoint, and'that must be considered mighty progress, for this jury would have every right to judge of an exhibition of paintings. Hitherto this new International Exhibition has found the greatest support in England. There, where formerly water-colour painting was more cultivated than on the continent, photography found a public trained to appreciate figure and landscape pieces; therefore the hopes that were connected with your countrymen’s taking part in this exhibition were not without justification; but even though, unfortunately, they refrained from doing so, that would not diminish the fundamental importance of this praiseworthy undertaking. Styx. ASTRONOMICAL TETESCOPES. * BY A. A. COMMON, F.R.S., TREASURER TO THE ROYAL ASTRONOMICAL SOCIETY. Note on a Method of Silvering Glass Mirrors. Solidions.—Make up 10 per cent, solutions of pure re crystallised nitrate of silver, pure caustic potash, and loaf sugar. To the sugar solution add } per cent, of pure nitric acid and 10 per cent, of alcohol. The sugar solu tion is very much improved by keeping, its action being more rapid and the film cleaner when the sugar solution has been made for a long time. Make up also a weak solution—say 1 per cent.—of nitrate of silver and a 10 per cent, ammonia (90 per cent, distilled water, 10 per cent, ammonia, "880 specific gravity). Distilled water must be used for all the solutions. Cleaning the Mirror. —Thoroughly clean the mirror. To do this pour on a strong solution of caustic potash, rub well with cotton wool, rinse with ordinary water, wash again with absolute alcohol, and rinse ; finally pour on strong nitric acid, and rub with a piece of cotton wool, inserted in the open end of a test tube. Rinse again thoroughly with ordinary water, and then place the mirror face downwards in distilled water in a dish sufficiently large to leave two inches margin round the edge of the mirror, and to keep the face of the mirror one inch from the bottom of the dish. The liquid should stand half an inch above the face of the mirror, which should not be completely submerged, and care should be taken to exclude all air-bubbles. For Silvering a 12-inch Mirror.—Take 400 c.c. of the nitrate of silver solution, and add strong ammonia until the brown precipitate first formed is nearly dissolved; then use the diluted ammonia until the solution is just clear. Then add 200 c.c. of the caustic potash solution. A brown precipitate is again formed, which must be dis solved in ammonia exactly as before, the ammonia being added until the liquid is just clear. Now add the 1 per cent, solution of silver nitrate until the liquid becomes a light brown colour, about equal in density of colour to sherry. This colour is important, and can only be pro perly obtained by adding the weak solution. Dilute ’ Concluded from page 91, the liquids to 1500 c.c. with distilled water. All being ready, add 200 c.c. of the sugar solution to 500 c.c. of water. Then lift the mirror out of the dish, taking care to keep its face downwards during the time it is out of the water, pour the washing water away, add the sugar solution to the silver potash solution, taking care they are thoroughly mixed, and pour them into the dish. Place the mirror face downwards in this solu tion, taking care to exclude all air-bubbles. The liquid will turn light brown, dark brown, and finally black. In four or five minutes, often sooner, a thin film of silver will commence to form on the mirror, and this will thicken until in about twenty minutes the whole liquid has acquired a yellowish brown colour, with a thin film of metallic silver floating on the surface. Lift the mirror out, thoroughly wash with distilled water, and stand the mirror on its edge, or rest it in an inclined position until it is dry ; if time can be allowed, the silvered mirror may be left to soak in distilled water, over night. Leave it to dry until next day, then the slight yellowish “ bloom ” can be polished off by rubbing softly with a pad of chamois leather and cotton wool. Care fully polish afterwards with a little dry, well-washed rouge on the leather pad. The film should be opaque and bril liant, and with careful handling will be very little changed with long use. Dishes.—Use porcelain, glass, or earthenware dishes whenever possible ; but, if these are not available, a zinc dish, coated inside with paraffin or best beeswax. For small mirrors (up to 12 inches) the easiest method of supporting them during silvering is to attach them to a wooden rod by pitch, and arrange the dish thus— Temperature and Time.—Half an hour is the usual time taken in silvering, but this is shortened by using warmer liquids. About 65° F. is best for silvering. In colder weather longer time must be allowed for the film to be deposited. In very hot weather a smaller quantity of sugar can be used, say 150 c.c. For a 12-inch mirror it is a safe rule to allow four times the time required to get the first indications all over the mirror as the total time for the mirror to be in the bath. In cases when it is necessary to silver face upwards, a band may be put round the mirror, and the solutions poured on. It is necessary, in this case, to leave out the potash solution, and allow a longer time for the silver to deposit; as much as two hours being sometimes neces sary. If a very thick film is required, two silvering baths can be used, the mirror being left in the first for fifteen minutes, then lifted out, rinsed with distilled water, and at once immersed in the second bath, which should be ready in a second dish. The film must not be allowed to dry during the operation of changing from one bath to the other. The North Middlesex Photographic Society.—-Lantern evening, February 23rd, “A Day at the Zoo.,” by Lewis Medland.