Voids
The following is a basic example of a void. A void is when any object intercepts blood from its intended flight path and therefore creating a void where blood should have landed if not for the object blocking it. This has sometimes been referred to as a ghosting effect. For this experiment I taped a small piece of denim to a white poster board to create a blocking effect. I created this stain by applying a small amount of blood on a board and then smacking that board with another.
Since the blood was intercepted by the square piece of denim, a resulting void pattern occurs.
Close-up of the piece of denim.