Ref: The synopsis of forensic medicine and toxicology-Dr.K.S.Narayana Reddy 28th edition pg no-247 age of blood stain fresh stains on light coloured clothes are of bright red colour,which gradually changes to reddish brown in 24hrs and brown within a few days which may become black after a long time .fresh stains are moist and sticky and on drying, they stiffen the cloth because of proteins. on many mettalic aicles, blood stains appear as dark shining spots or smears or when dry show fissures and cracks . in ordinary condition a drop of blood dries in an hour or two. the recently shed aerial blood is bright red and venous blood is dark red. the fresher the blood the more easily it dissolved in water. fluorescence decreases as stain become older. it can only be stated that the stain is very fresh,recent,some weeks or months or very old-luminol spray-blue flourescence. Forensic investigators use luminol to detect trace amounts of blood at crime scenes, as it reacts with the iron in haemoglobin. Biologists use it in cellular assays to detectcopper, iron, and cyanides, as well as specific proteins by western blot. When luminol is sprayed evenly across an area, trace amounts of an activating oxidant make the luminol emit a blue glow that can be seen in a darkened room. The glow only lasts about 30 seconds, but investigators can document the effect with a long-exposure photograph. Crime scene investigators must apply it evenly to avoid misleading results, as blood traces appear more concentrated in areas that receive more spray. The intensity of the glow does not indicate the amount of blood or other activator present, but only shows the distribution of trace amounts in the area.