How to use Oxalic acid

How to use Oxalic acid

How Oxalic Acid Is Made

Oxalic Acid derived from common vegetables such as spinach, rhubarb and sorrel. The extraction process typically means oxidizing carbohydrates and glucose in this plant vegetation with either nitric acid or vanadium pentoxide. This process creates powdered crystals that activate completely when mixed with hot water, making it simple to store between uses and mix when needed.

What Exactly is Oxalic Acid (and how it works)

Now that you know how to bleach wood with it, it would be helpful to understand what exactly is Oxalic acid. Usually, oxalic acid comes packaged in a crystalline form that is to be dissolved in hot water before use. When dissolved in hot water, Oxalic acid is completely activated.

Chemically, it is known as ethanedioic acid, a compound found naturally in certain plants. When Oxalic acid in the natural form is processed, it becomes inorganic and toxic. This form of Oxalic acid is famous for wood bleaching and commercially available for other uses.

When wood is exposed to water or metal for an extended period, blotchy stains and marks begin to appear on the wood. These blotchy stains are referred to as Iron oxide stains. They arise due to the reaction between tannin present in wood and trace iron oxide from metals or water.

Iron oxide stains are solely responsible for most stains in wood. Other stains may be caused by heat marks, inks, dyes, etc.

Oxalic acid has been shown to produce amazing results when used for wood restoration. It is a preferred choice of bleach because it removes all kinds of stains without tampering with the color of the wood.


Quick Tips for Bleaching Wood

Now that you’ve determined what type of bleach to use for your project, you will need to follow a few quick tips for the bleaching process. Here are a few of my favorite tricks:

  • Follow all safety precautions when using all of these methods. When working with chemicals, you should always follow the product instructions.
  • Use sunlight to help speed up the process. I only have experience to quote here, but I’ve found that bleaching a piece of furniture and leaving it in the sun for several hours helps the final outcome. If anything, it will help it dry quickly.
  • Neutralize and clean the piece after bleaching. It helps when sealing or staining the final piece. You do not want it to continue oxidizing and you’ll want to make sure the final products can be applied effectively and safely. I’ve found a mixture of 50:50 vinegar to water does the job. When neutralizing oxalic acid, you can use household baking soda mixed with water.
  • Lightly sand after bleaching and neutralizing the wood. The chemicals might cause slight damage or rough spots in some places that might not be visible but will show up when stained or sealed.

In conclusion, there are several methods for bleaching wood and it’s important to determine your end goal when selecting a method. Are you looking to clean and remove stains or are you looking to completely lighten the piece? All of these questions will help determine the best method for you!

More Furniture Tips

Photography Credits: Caitlyn Motycka Photography

Alternatives to Wood Bleaching

If you don’t wish to pass through the stress of bleaching wood, other methods can be used for removing stains and restoring an old piece of furniture or wood.

For Really tough stains

  1. White vinegar and bicarbonate of soda: Add a few drops of white vinegar to baking soda and mix until a paste-like consistency is formed. Rub the mixture on the stain and wipe it off with a damp piece of cloth. This mixture is effective for removing dyes and other similar stains.
  2. Sandpaper: Stains that seem resistant to bleaching can be sanded. With fine sandpaper, gently sand out the stain and its surrounding areas. If need be, sand out the whole surface area to keep the color even.
  3. Isopropyl alcohol: Isopropyl alcohol is effective for clearing out stains like pen and ink. Using an old clean cloth, rub isopropyl on the surface and wipe out thoroughly. Once the stain is gone, clean the wood with a damp soapy cloth and allow the surface to dry.

   For less tough stains

  1. Petroleum jelly: Apply petroleum jelly on watermarks and allow to sit overnight before wiping off.
  2. Baking soda and non-gel toothpaste: For heat marks on wood, combine non-gel toothpaste and baking soda. Rub the resulting paste on the wood with a cloth till it begins to feel warm before wiping off. Keep repeating the process until you are certain the stain is completely gone. Smoothen out the wood with oil or polish it after.

How to Use Wood Bleach

When you’re ready to start your wood bleaching project, gather all the necessary supplies in the area you plan to work. Again, when working with strong chemicals, be sure the area is well-ventilated and large enough that you can move around easily as you work through the process.

Cleaning Surfaces

Cleaning Surfaces

Oxalic Acid works on bare wood, so the first step to using this formulation is cleaning your surface thoroughly. This means clearing away old finishes, and The Real Milk Paint Co. has you covered there with stripping products designed for practically any finish you need to clean. For surfaces covered in modern paints and urethane, consider using Soy-Gel Professional Paint Remover, which removes several layers of shellac, paint and other finishes with one application. This low-VOC formula offers powerful stripping yet is safe enough for indoor use. Use Milk Paint Stripper for surfaces covered in Real Milk Paint. Once you’ve stripped the surface or if you’re working with bare wood, then wipe the surface down with Trisodium Phosphate to completely remove any residue.

Mixing Oxalic Acid

When using Oxalic Acid from The Real Milk Paint Co., mixing is simple. For smaller batches, mix 2 tablespoons of our Oxalic Acid powder with 2 quarts of hot water in a glass or ceramic container. For larger jobs, mix the entire package with 2 gallons of hot water. Remember, acids typically weaken over time, so your Oxalic Acid mixture works best when freshly mixed.

Apply Wood Bleach Mixture

Grab an old scrub brush, paintbrush or mop once you mix your solution, then use it to liberally apply Oxalic Acid to your surface. Be sure to wipe off any of the solution that splatters on other surfaces, and keep the Oxalic Acid solution on until the wood reaches your desired level of lightness. If the stain is still there after the solution dries, reapply it with the same technique and allow it to dry again.

Neutralize the Oxalic Acid

When you achieve the look you want, neutralize the Oxalic Acid solution with Borax. To do this, mix 2 tablespoons of Borax with 1 quart of water, then apply the mixed solution liberally over the surface. Though this isn’t a hard step you must perform, it does help ensure a safer working environment and reduces injury risks as you complete your project. Once the solution dries, you’re ready to rinse the surface with water.

Rinse the Treated Area with Water

Once the wood achieves the lightness level you prefer, rinse the treated area with water. You likely need to rinse the area multiple times to be sure you’ve removed all the Oxalic Acid, so don’t be shy about rinsing. When you finish, allow the bleached finish time to dry. It’s very important to remove neutralize and rinse away residual Oxalic Acid. So, don’t be afraid to repeat these steps if necessary.

Check for Residue

Once you’ve treated the wood, rinsed it clean and allowed the surface to dry, use the dark rag in your supplies to check for residue. To do this, simply run it across the dried surface, then check it for any powder left behind. If you find residue on the dark rag, then repeat the rinsing step and check for residue again. Once your rag comes back clean, move on to the next step.

Complete Your Build or Restoration

Once your surface reaches the desired level of lightness and you’ve rinsed, neutralized and removed all residue, you’re ready to add color or shine to the wood. Because your wood is bare and now clean, you can simply work as usual with your choice of Real Milk Paint colors, finishing creams or glazes or waxes such as Good Ol’ Brown Wax or Soapstone Sealer and Wood Wax.

Getting the look you want from the original wood used to build antiques doesn’t have to be tricky when you use Oxalic Acid to remove stains or restore surfaces to their original beauty. Safe and effective when you take the proper precautions, Oxalic Acid works equally well for experienced and beginner DIYers, with a forgiving formulation that doesn’t make your surface lighter than it was originally. By combining Oxalic Acid with other products from The Real Milk Paint Co., you can beautify vintage pieces with ease and create new furnishings or flooring that mimics the look of antiqued items without breaking your back or your budget.


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