Which preposition to use with illuminative

of Occurrences 2%

It was illuminative of her real character and of her real mind as to Ross, and as to Dory also, that, instead of being crushed by her brother's look of downright horror, she straightway ejected the snobbish suggestions with which her vanity had been taunting her, and called her heart, as well as her pride, to the defense of Dory.

Which preposition to use with  illuminative