The Staining Properties of Motion Picture Developers

Abstract

When Most developing agents become oxidized either by the oxygen in the air or by virtue of performing useful work in reducing a silver emulsion to metallic silver, they are converted to colored products which behave like a solution of a dye towards the gelatin coating on film and stain it uniformly. With developers like pyro, which in alkaline solution readily oxidizes to a reddish brown compound, more or less of the colored oxidation product is deposited along with the silver image during development so that a stain image is obtained. This image increases the effective contrast of the negative but is usually accompanied by more or less general stain. <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sup> Elon and hydroquinone oxidize much less readily than pyro, and in the case of an average elon-hydroquinone motion picture developer which contains a relatively high concentration of sulphite, the rate of oxidation is comparatively slow. The oxidation products of the hydroquinone in this case are most probably hydroquinone mono and di-sodium sulphonates <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> which are colorless. The mono-sulphonate is a weak developer and the di-sulphonate does not develop at all. This explains why certain elon-hydroquinone developers on standing in an open tray for two or three days at room temperature may lose their developing power although they become only slightly colored.