Oxalic acid is used to bleach wood when it has been stained by iron. There are many ways iron works it’s way into wood and this is the best remover for those stains when you are working on refinishing wood surfaces. Weighs 16 oz.
Have you ever removed the finish from a piece of furniture and found black stains or black rings from metal pots or prolonged water exposure? Have you ever removed the finish from a floor and found black or deep brown pet urine stains in the wood, which no amount of sanding will take out? These are all iron stains caused by the chemical reaction of tannins in the wood mixing with the trace metals in urine and water.
Oxalic acid is an all-natural, organic compound. It’s found in vegetables like sorrel, spinach and rhubarb. There are many processes to extract it from vegetation, but modern methods manufacture it through the oxidation of carbohydrates or glucose using nitric acid or vanadium pentoxide. It is a relatively strong acid for its acid group. It is important to use protective gear and eye goggles when handling oxalic acid.
The main use of oxalic acid is as a bleach, particularly with wood and to remove iron stains all while not bleaching the wood. (If you do want to remove the natural color of wood, you would need a two part bleach of sodium hydroxide and hydrogen peroxide.) For small spots, it is suggested that users mix about two tablespoons of it in a quart of hot tap water and allow it to dissolve. For larger spots, or entire sections of a floor, there are directions on the next tab. Wood bleach is also great for removing water spots and rust stains.
When dissolved, use an artist brush and paint it in the mixture on the stained areas only. Allow to dry. The stain will lighten. If it does not disappear, then do another coat. You may need to coat it three or four times, allowing time to dry between coats. Once the stain is gone you can sometimes get a slight halo effect around the area where the stain was bleached. To take care of this, saturate a rag with the acid solution and wipe a thin coat over the stain and surrounding area. Allow to dry. This should take care of the stains. Once the stains are gone you need to neutralize the acid so it will not react with your wood finish. Mix up two tablespoons of borax in a quart of hot water. Saturate a rag with the borax solution and wipe the floor and allow to dry. Borax, like oxalic acid, is a natural product.