Reply by a1Jim

Oxalic acid works well on rust and dark spots left on wood

2 part bleach works best of the these two ,one part is a high percentage peroxiode only available through beauty supply stores to Lic hair dressers of in this 2 part bleach

The strongest is swimming pool bleach “Shock it “

All bleaches are dangerous,so eye protection including long sleeves,rubber gloves plus using it in outdoors or a very well ventilated area and a respirator.
Never mix bleaches they can create poison gases.
Before you finish or switch types of bleach you need to neutralize your wood with a 50/50 solution of water and baking soda ,some times more than once and let dry.

-- W James Brokenbourgh Custom furniture maker http://artisticwoodstudio.com/