[The use of remission analysis for direct colorimetric determination of age of blood stains (author's transl)].

A review is given of the conventional methods of determining the age of blood stains by forensic examination of trace evidence. Detailed analysis of the samples in several steps, which destroyed the traces, and the widely differing results do not appear satisfactory with regard to their use in forensic investigations. Considering the change in color with increasing age the three coloric parameters (chroma, hue, and value of the blood stain) can yield exact numerical measurements which allow to draw relatively reliable conclusions as to the age of the blood stain. Of the three colorimetric methods, based on equalization, three regions, and spectral analysis, respectively, only the last may be considered really satisfactory and up to the requirements of forensic medicine. It has the additional advantage of being independent of the visual acuity of the examiner and of the type and quality of the source of illumination. The aging of freshly taken venous blood, which has been deposited on filter paper or linen, can last up to 33 days, either in the dark or in day light, with due regard to temperature and humidity. The spectrophotometric color measurements taken place on the immediate surface of the blood stain in the range of the visual spectrum between 400 and 600 nm. The continuously drawn spectral curves are then subject to remission analysis the first step. The second step consists in a mathematical computer analysis of color valence measurements.