Border occasionally seen between Light and Dark Regions on Photographic Plates

Abstract

THE reason mentioned by Sir Oliver Lodge (p. 5) for the border seen between light and dark regions on photographs is not the only one. In the denser regions of a negative the developer gets more exhausted or restrained than in the thinner regions, and this affects the adjacent parts. At the junction of a dense and a thin area the edge of the thin part is made thinner by the restraining compounds (bromide, oxidised pyrogallol, &c.) derived from the denser part, while, on the contrary, the edge of the denser part is made denser by the less exhausted developer flowing from the thin area. This effect is apt to be the more marked when the developer is already well restrained, as by staleness or the addition of much bromide.