I have. I wouldn't call the results Bad, but it's kinnda a waste of good auqafortis. Most walnut is dark to begin with and show's it's own natural grain in darker tones. The auqafortis will/can turn the wood almost black after it's neutralized and the first coat of linseed or clear coat is put on. Then it's too late! Unless you want super dark, and little to no grain showing, your better off to just finish the Walnut natural