BUBBLES ON PLATES AND PAPERS Bubbles or air-bells frequently form on plates and papers during development, and they have the effect of preventing the developer acting on the spots covered by them. The result is clear glass spots upon the negative or white spots upon developed prints. Bubbles invariably arise from stale or frequently used developer, particularly pyro, or they are caused by a care less and uneven flowing of the solution over the surface to be developed. Soaking the sensitive material in water previous to development also causes bubbles to form on the film. A huge crop of tiny clear spots—the result of bubbles—of an irregular form and appearing mostly at or near the edges of the negative, is generally due to an old or oxidised developer, or to one that has been allowed to stand even for a short time after mixing. Larger, round spots are caused by bubbles which attach themselves firmly to the sensitive surface during a preliminary soaking in water, or when the developer is poured on rashly and unevenly. Spots with small black centres are also caused by bubbles ; these form during development and cause the gelatine under them to be harder than the developed portions, and therefore slower in fixing, the result being the small specks of unfixed silver bromide in the centres of the spots. The methods of preventing
bubbles are obvious. The plate or paper should not be soaked in water before the developer is applied ; the developer should be freshly mixed, and poured on to the sensitive surface in an even sweep, first along one edge, and the dish then tilted so as to cover the surface as quickly as possible ; the dish should be rocked slowly and regularly, and not violently and in sudden jerks. Many workers pass a clean broad camel-hair brush, a pad of cotton-wool, or a Buckle brush over the film as soon as the developer is poured on, so as to break up and remove any possible bubbles ; the brush must, however, be quite clean and soft, or the remedy will be worse than the disease.