KODAK professional B/W Duplicating Film/4168 (formerly KODAK Professional Direct Duplicating Film SO-015 (ESTAR Thick Base) is used for one-step duplication of continuoustone, black-and-white negatives and positives. Using current recommended processing procedures, good dark-keeping properties are obtained at 70° F (21°C), 40% RH; projection of the Årrhenius temperature-time tests indicates that the negatives stored at 70°F, 40% RH will be useful for making prints for well over 100 years. When subjected to dark-keeping conditions 140°F (60°C), 70% RH for 30 days, the film passes the ANSI PH 1.41-1981 tests. However, there is an image-tone change from almost neutral to a slightly brown tone, but prints made from these negatives are indistinguishable from those made from the original negative. Lightstability tests show that when 4168. Film negatives are subjected to extremely high levels ofradiant energy for an extended time, or exposure to oxidizing gases such as hydrogen peroxide vapor the silver images that were originally close to neutral will change in tone to yellow-orange color in the same manner as many other black-and-white photographic images.