Giorgio Vasari, Lives of the Most Excellent Painters… (1850)
“ So powerful indeed were these emotions of anger and bitterness, that Andrea began to consider if he could not by one means or another remove this competitor from his sight. Andrea dal Castagno was no less subtle in dissimulation than clever as a painter; he could assume a cheerful countenance at his pleasure, had a ready tongue, was a man of a bold spirit, and was as decided in acting as in resolving; he had the same dispositions towards others as towards Domenico; and when he perceived a fault in the work of an artist, would mark it secretly with his nail. ”
