Few things are more frustrating than spilling something on your wood furniture and having to deal with the resulting stain. Simply wiping the wood down with conventional cleaners will almost never do the trick, and using too much water can actually make the situation worse.
Furthermore, improper scrubbing or wiping the wood with the wrong materials can cause further damage, which may be irreparable if the wood is degraded or the stains reach far enough below the polish. Fortunately, if you haven't yet ruined the stained spot with a failed cleaning attempt, it is relatively easy to remove both light water stains and dark iron stains from wood furniture using the following techniques:
Removing Light-Colored Water Stains
First, if you have white stains on your wood furniture, try rubbing some mineral oil onto the spot using a soft cloth. Let the oil sit on the spot overnight, and if it appears to be working the next morning then repeat with another rubbing.
If the stain has been absorbed into the wood's finish but has not yet made its way into the wax layer, and mineral oil isn't getting the job done, then rubbing the areas with mineral spirits on a soft cloth may work. Be sure to wear gloves while doing this in an area with good ventilation. If the mineral spirits get rid of the stain but leave the spot looking duller than the rest of the wood, then cover the furniture’s surface entirely with mineral spirits and then apply a coat of good quality polish formulated for wood furniture.
If mineral spirits aren't effective, try rubbing the spot with a mixture of baking soda and toothpaste. Rub with the grain until the discoloration is diminished and then clean the spot with an oil soap. Sometimes it can take a couple applications of this mixture before the stain will start to come out. Once the stain is gone, use furniture wax to coat the wood.
Use Sandpaper to Remove Dark Stains
Sometimes you can get rid of dark stains by simply removing the stain’s finish with some sandpaper. Rub the spot with #100-grit sandpaper moving back and forth along the wood’s grain. Once you're done with the initial step of removing the finish, the edges of the spot can be feathered with #150-grit sandpaper.
Next the stain itself should be sanded with the sandpaper (#150-grit) and here the edges can be feathered with fine steel wool. Once the stain has been sanded out, use a tack cloth to eliminate the dust from sanding, and then put on varnish, just a couple thin coats, that will blend the sanded spot to the original finish. The edges of the newly varnished area should be feathered to smooth out the difference between the new and old varnish. Finally, polish the wood with a high quality product.
Removing Dark Brown or Black Iron
Stains With Bleach
Should the stain be too far down to reach with aggressive sandpapering, you might need to resort to using oxalic acid wood bleach to penetrate deeper into the wood and remove the stain. Put on the bleach over the stained spot using a brush and wearing rubber gloves.
Next comes the waiting game. Let the bleach sit on the stain for a time, a few hours is recommended. The spot will slowly begin to fade to the original color. Check on the stain periodically, and once the color of the wood has been restored to its original state, wipe the area clean with a wet sponge to prevent excessive bleaching and fading.
After cleaning the bleach off you'll need to counteract the chemicals on the area by applying vinegar. After allowing the wood to dry, the wood can be stained if needed. Finally, apply a few light coats of varnish to the spot, smooth the edges of the varnish with #1000-grit sandpaper, and wax the entire surface with a wood polish.