For investigative purposes, I'm searching for a tool that can be used as a quick visual assessment of the the length of time that blood has been exposed to air after the blood flow has stopped.. Let's say that you walk into a room and see someone unconscious. Where blood appears, it had already stopped any fresh flow & has already dried to a dark brown similar to mahogany wood. That person has been there longer than how many minutes? Please understand that I'm not asking how long the person has been lying there but for at least how long?
You come upon a dazed person unsteady on their feet with an injury to the face. The blood flow has stopped: the person may have smeared the blood when touching their face but you see that the blood has not changed to a deep brown and still retains a bright red color..approximately how much time has likely elapsed between the injury occurring and your encounter with the injured person?
I know there's no exact time estimate possible without testing but simply for quick field assessments, is anyone willing to hazard an opinion?
In summary: How can I tell the age of a blood stain?