LIGHT INSENSITIVE PHYSICAL DEVELOPERS

Within the pH range 2.5-6.5 tungstic acid (an isopolyacid) prevents the reduction of silver ions by ascorbic acid or hydroquinone more effectively than either gum acacia or other protective colloids. The colloid state of tungstic acid can be stabilized with nonionic detergents, especially with Triton X-100. For buffering the system a mixture of acetic acid and sodium acetate is optimal. Physical developers constituted on the basis of the observations are, in contrast to those commonly used in histology, light insensitive, and remain clear for about 30 min at mom temperature 2-5 times as long as the time required for development. © 1979 Informa UK Ltd All rights reserved: reproduction in whole or part not permitted.