TAKE THE necessary safety rules. IT is an ACID un the range Phofurus Acid and can harm a lot mainly eyes both in unprotected skin and gives burnsOxalic acid works great on grey weathered wood and gray water stains, but not much else. The two component wood bleach is the only thing I've found that will lighten a dark wood-
Don't use steel wool on the wood before bleaching- the tiny bits of steel left behind will turn into tiny black dots that I never was able to get rid of.Amazon.com: Zinsser 300451 Wood Bleach, 8 oz: Home Improvement
Amazon.com: Zinsser 300451 Wood Bleach, 8 oz: Home Improvementwww.amazon.com