When restoring older wood furniture you will probably encounter dark rings and black spots, which are caused by water stains. Oxalic acid is a moderate bleach that will remove these stains even if they have penetrated the wood surface. Oxalic acid will also remove finish stain applied previously and lighten the wood for a fresh new look. Restoring wood furniture takes time and patience, but the results of your labor can be enjoyed for years, even generations. The restoration process usually involves stripping off old finishes, bleaching, staining and then varnishing.
Once you have stripped the old varnish and paint from a piece of furniture, you will most likely encounter stains in the wood surface that should be removed before applying a new finish. Bleaching is a good technique for getting out these stains. However, different types of stains require different bleaching techniques. For a solution to suit your own DIY wood restoration project, consult this great how-to.