Which preposition to use with unblenching

on Occurrences 2%

But while man aspires after truth, while his brain yearns after knowledge, while his intellect soars upward into the heaven of speculation and "beats the air with tireless wing", so long shall those who demand faith be met by challenge for proof, and those who would blind him shall be defeated by his determination to gaze unblenching on the face of Truth, even though her eyes should turn him into stone.

Which preposition to use with  unblenching