And they took ashes of the furnace,.... 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, and raised blisters and blotches; and hence arose those lying scandalous stories of the Israelites being a scabby people, and of their being driven out of Egypt on that account, affirmed by Manetho, Lysimachus, Diodorus Siculus, Tacitus, Justin, and others; See Gill on Exodus 4:6 with this plague the first vial poured forth on mystical Egypt, or antichrist, has some agreement, Revelation 16:2.

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.

9:10 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.

10. 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 [De 4:20; 1Ki 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.

9:8-12 When the Egyptians were not wrought upon by the death of their cattle, God sent a plague that seized their own bodies. If lesser judgments do not work, God will send greater. Sometimes God shows men their sin in their punishment. They had oppressed Israel in the furnaces, and now the ashes of the furnace are made a terror to them. The plague itself was very grievous. The magicians themselves were struck with these boils. Their power was restrained before; but they continued to withstand Moses, and to confirm Pharaoh in his unbelief, till they were forced to give way. Pharaoh continued obstinate. He had hardened his own heart, and now God justly gave him up to his own heart's lusts, permitting Satan to blind and harden him. If men shut their eyes against the light, it is just with God to close their eyes. This is the sorest judgment a man can be under out of hell.