Exodus 9:10

“And they took ashes of the furnace, etc.] Which was near at hand, perhaps in Pharaoh’s kitchen: and stood before Pharaoh; not in his palace, or in any covered room, but in some place open to the heaven, a courtyard or garden adjoining to the palace: and Moses sprinkled it up towards heaven; cast it up in the air; this being again ascribed to Moses, seems to confirm the notion of those who think he only did it; but, for the reasons before given, both may be thought to be concerned: and it became a boil breaking forth with blains, upon man, and upon beast; these failing down in the manner before described, on whomsoever they lighted, whether man or beast, produced sore boils and inflammations,…”

“Moses took ashes from the furnace--Hebrew, "brick-kiln." The magicians, being sufferers in their own persons, could do nothing, though they had been called; and as the brick-kiln was one of the principal instruments of oppression to the Israelites [Deu 4:20; Kg1 8:51; Jer 11:4], it was now converted into a means of chastisement to the Egyptians, who were made to read their sin in their punishment.”

“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, Deu 28:27, as if it were some new disease, never heard of before, and known ever after by that name. Exodus 9:11”

“a boil: Deu 28:27 Exodus 9:11”