How Long Does It Take for Blood to Dry?
A study published in the International Journal of Legal Medicine reported that a blood drop on a hard surface in a typical indoor setting at 20 degrees Celsius is completely dry in 60 minutes. Increasing the temperature to 24 degrees Celsius reduces the drying time to only 30 minutes.
HowStuffWorks says that the time it takes blood to dry depends on the type of surface the blood is on, the amount of blood present, the temperature and the humidity. The MadSci Network says that the time required for blood to dry can also be influenced by medical conditions afflicting the blood donor.