I really pondered how gross festering boils would be: all of the puss and fluid and oozing. I feel pretty confident that I managed to capture that in this rather icky painting.
Then the Lord said to Moses and Aaron, “Take handfuls of soot from a brick kiln, and have Moses toss it into the air while Pharaoh watches. The ashes will spread like fine dust over the whole land of Egypt, causing festering boils to break out on people and animals throughout the land.”
So they took soot from a brick kiln and went and stood before Pharaoh. As Pharaoh watched, Moses threw the soot into the air, and boils broke out on people and animals alike. Exodus 9:8-10