¹ Then the Lord said to Moses and Aaron, “Take handfuls of soot ²  from a furnace, and have Moses throw it ³  into the air while Pharaoh is watching. ⁴ 

So they took soot from a furnace and stood before Pharaoh, Moses threw it into the air, and it caused festering boils to break out on both people and animals.

Now Mount Sinai was completely covered with smoke because the Lord had descended on it in fire, and its smoke went up like the smoke of a great furnace, ¹  and the whole mountain shook ²  violently.