What happens to blood as it dries over time?

As blood dries over time, it undergoes a series of changes in color due to the oxidation and dehydration of hemoglobin, the protein responsible for red blood's color. Initially, fresh blood appears bright red, but as it begins to dry, it oxidizes and changes color.

This transition begins with the blood darkening to a red-brown hue as the moisture evaporates and the iron in hemoglobin oxidizes. Over a period of time, as drying continues, the color further fades and can eventually become brown in appearance. This process not only reflects the physical changes in the blood but also indicates the stages of drying and the chemical breakdown occurring due to exposure to air and the environment.

This gradual shift in color provides forensic scientists with important information regarding the age of bloodstains at a crime scene, as well as the conditions under which the blood has dried.