I did a study of blood last night before I passed out. I had no samples to work with, so here it is with peliminary rules :
A fresh blood pool (not splatter) is bright red. The edges are beveled as it does have round edges off the floor, but not much. Blood shines along the edge of the pool facing the light.
Several days later, blood turns black and cakes. It breaks like mud and leaves watery stain in between the larger "mud" cakes.