Wooden furniture and flooring can stain and darken over time. Or sometimes, it's just too dark in the first place. Here's a simple way to lighten it.

A: Oxalic acid is a potent but toxic cleaner that removes rust and stains caused by iron, water and tannic acid. It's available in dry crystal form, to be dissolved in warm water for use.

But, if it's been a long time between refinishes, a commercial deck cleaning solution with oxalic acid (wood bleach) may be necessary to remove the dirt, gray coloring, mildew, and stains.

Instead, use a cleaner containing oxalic acid (wood bleach), such as Flood Wood Cleaner or Behr Premium All-In-One Wood Cleaner. In most cases, apply it with a paint roller, paintbrush, or garden ...

The classic treatment is oxalic acid, which is sold at some paint stores for use as a wood bleach. It is often sold in small bags. To use oxalic acid, mix one-half cup of the powder in a gallon of ...

(Behr All-in-One Wood Cleaner, which has oxalic acid as its sole listed ingredient, is $9.98 a gallon at Home Depot.) Be sure to read the label for safety precautions, ...

Make a solution of oxalic acid crystals (available in paint stores) to saturation in hot water in a plastic bucket; never use metal with oxalic acid. Apply it to the stains with a paintbrush.