Originally posted by Nephthys
I recall that it was said that the venom had eaten a hole in Gregor's flesh, but that was quite a while after the fight and that could just be the wound festering etc. So dunno if its seriously acidic enough to burn through plate mail.
Originally posted by A Feast for Crows, pages 110 - 111
"Ser Gregor." Qyburn shrugged. "I have examined him, as you commanded. The poison on the Viper's spear was manticore venom from the east, I would stake my life on that."
"Pycelle says no. He told my lord father that manticore venom kills the instant it reaches the heart."
"And so it does. But this venom has been thickened somehow, so as to draw out the Mountain's dying."
"Thickened? Thickened how? With some other substance?"
"It may be as Your Grace suggests, though in most cases adulterating a poison only lessens its potency. It may be that the cause is . . . less natural, let us say. A spell, I think."
Is this one as big a fool as Pycelle? "So are you telling me that the Mountain is dying of some black sorcery?"
Qyburn ignored the mockery in her voice. "He is dying of the venom, but slowly, and in exquisite agony. My efforts to ease his pain have proved as fruitless as Pycelle's. Ser Gregor is overly accustomed to the poppy, I fear. His squire tells me that he is plagued by blinding headaches and oft quaffs the milk of the poppy as lesser men quaff ale. Be that as it may, his veins have turned black from head to heel, his water is clouded with pus, and the venom has eaten a hole in his side as large as my fist. It is a wonder that the man is still alive, if truth be told."
Originally posted by Epicurus
Maybe whatever black magic Oberyn performed on the venom caused it to develop corrosive properties.
Then of course there's the issue of the spear tip being unaffected by the speculative corrosive properties of the poison.