Oiling of Plates for Ultra-violet Photography

Abstract

IT has long been known that a substitute for the Schumann plate for ultra-violet spectroscopy beyond 2500 A. can be made by oiling the surface of the plate. These oiled plates were found by Harrison (Jour. Optical Soc. Amer., vol. 11, pp. 113 and 341; 1925) to be in some respects superior for photometry, as Schumann plates are rather uneven, having spots of greater sensitivity. All the methods so far suggested for oiling the plates are rather messy and involve the cleaning of the plate before development. There is also a loss of sharpness due apparently to the thickness of the oil coating. The following method used by me seems to overcome these disadvantages and may be of interest to other workers in the subject. I use a filtered solution of 5 grams of vaseline in a litre of petroleum ether. The quantity of vaseline may be increased for certain work. The plates are flooded with this solution in a dish and lifted out and rapidly dried. After exposure they can be developed without further treatment by the ‘stand method.’