Stained
Wood can be stained with water, oil or with fungi and the discoloration may be hard to remove if more than a light sanding is necessary. Water damage on wood, from wet pots left on porches or interior floors is usually gray brown. Oil can sometimes be poulticed out using damp rags and a formulated clay. Some stains can be lightened with bleach, but often the stain will remain. If the wood has been finished with a penetrating stain, it may be possible to use a darker stain to mask the stain (once cleaned).