Ashes of the furnace — Sometimes God shews men their sin in their punishment: they had oppressed Israel in the furnaces, and now the ashes of the furnace are made as much a terror to them as ever their task — masters had been to the Israelites. This is afterwards called the botch of Egypt, Deuteronomy 28:27, as if it were some new disease, never heard of before, and known ever after by that name.
Related Commentaries of Exodus 9:10
Exodus 9:10
10 And they took ashes of the furnace, and stood before Pharaoh; and Moses sprinkled it up toward heaven; and it became a boil breaking forth with blains upon man, and upon beast.