Air Brush Alabastrine Process
brush or pencil before printing from the negative. Air bells in the developer frequently adhere with great tenacity to the gelatine film, and give rise to places of less density than the surrounding parts, or even clear glass. It is always advisable to pass the fingers over the plate when first covered with the developer, or a flat, soft camel's-hair brush may be kept for this purpose. If a brush be used care must be taken that it is well washed after use and does not come into contact with any chemical or foreign matter, which would cause streaks on the finished negative.
Air Brush. This is an American invention, by means of which liquid colours can be applied as spray to enlargements and prints. Air is pumped by means of a foot-blower through a chamber terminating in a fine orifice, the liquid colour being led to the opening by a movable needle or fine tube, where it is converted into a fine spray by the blast of air. A new and more portable form of air brush, similar in form to a pencil, is known as the aerograph. A form of air brush is now occasionally used in painting large surfaces, especially when they are irregular, and the ordinary methods of painting would be troublesome. An air brush may be used in vignetting negatives and in painting back-grounds. The principle of the air brush has been applied to the coating of glass plates with emulsion and to the coating of paper with photographic preparations. With proper precautions and suitable adjustment of the fineness of the spray, it gives an even and not granular coating; but allows of adjustment by which any required degree of granularity can be obtained. An ordinary spray-producer, such as is sold by perfumers, may be used to coat paper with gum bichromate mixture, or any thin sensitive preparation.
Alabastrine Process. An old process for improving the colour of wet collodion glass positives. It can be applied to gelatine negatives in the following manner (absolute freedom from stains and hypo being a sine qua nori): - Soak the negative in clean water till thoroughly moist, and then in following solution : perchloride of mercury, 40 grs., dissolved in pure • hydrochloric acid, 1 drm. ; chloride of sodium, 20 grs.; sulphate of iron, 20 grs.; distilled water, 2 ozs. Allow the positive to soak till thoroughly bleached; wash, dry, and varnish the back with matt black varnish, or back with black velvet.