Oxalic Acid Dihydrate Crystals 99.6% (100g)

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"The most effective way to remove stains from wood, including water, mildew, ink and rust".

Oxalic Acid Dihydrate Crystals. Purity: 99.6%. Size: 100g. Just add water. Will make approximately 1 litre of oxalic acid at 10% solution or 2L at 5% solution.

Oxalic Acid Wood Bleach is a versatile and powerful solution designed to rejuvenate and restore the natural beauty of wood by effectively removing dark stains such as ink or rust, water marks and restoring the wood's natural colour. This product is particularly beneficial for oak, walnut, mahogany and teak woods.

Key applications include:

  • Eradicating black or dark stains on various wooden surfaces such as kitchen worktops, external oak structures, wooden doors, and floors.
  • Removing tannin stains to restore wood's natural appearance.
  • Effective rust stain removal from concrete and metal, providing a clean and refreshed look.
  • Eliminating water marks, restoring the pristine condition of the wood.
  • With a purity grade of 99.6%, our Oxalic Acid Wood Bleach guarantees high-quality performance for both professional and DIY projects.


Table: Required Amount of Oxalic Acid Crystals

Solution Strength
5% 10%  
50ml 2g 5g
100ml 5g 10g
250ml 12g 25g
500ml 25g 50g
1.0L 50g 100g

Material Safety Data Sheet (MSDS) 


How To Use Oxalic Acid on Bare Wood

Wear protective clothing: Rubber Gloves, Face Mask and Safety Glasses. Keep away from children.

The solution can be applied directly to the stained area for spot removal or it can be used as a general wash over the entire surface.


  1. Apply the hot solution to bare wood with a brush, sponge or cloth to help remove unwanted stains and revive the natural colour of the wood
  2. Ensure you rinse the surface thoroughly with clean fresh water to remove any excess oxalic acid. If you don't properly wash off the treated area, there is a strong chance that it will react with any newly applied finish: Preventing drying of the finish and or blistering of the finish
  3. If you are trying to avoid raising the grain of your wood surface you can alternatively use methylated spirits to dissolve the oxalic crystals. The advantage being a quicker drying time for finishing

Can you use oxalic acid on veneer?

Yes you can use it on veneered and solid wood furniture

*Trade Tip* - Soda Crystals
A neat trick I often employ when using oxalic as a reviving wash:

Neutralising the oxalic with a hot solution of soda crystals

  1. Mix the soda to the same ratio as the oxalic 10:1 in very hot water.
  2. Apply the soda solution shortly after you have applied the oxalic and you will see it react immediately.
  3. You can repeat this process but its effectiveness will lessen with each process

**We do not guarantee by using this product it will remove all stains. Some wood species can be resistant to the bleaching process of oxalic acid in solution.

Frequently asked questions

What is oxalic acid, and what is its purpose in woodworking?

It is a naturally occurring organic compound that is often used in woodworking for its bleaching and cleaning properties. It is particularly effective at removing stains caused by water, rust, tannins and at lessening the marks left by ink pens, coffee and tea.
Oxalic acid will often help restore the wood's natural colour prior to refinishing.

How do I safely use it on wood?

When using oxalic acid, it's essential to take safety precautions since it can be harmful if ingested, inhaled, or if it comes in contact with the skin. Use gloves, goggles, and a dust mask when working with oxalic acid. To use it on wood, dissolve the oxalic acid crystals in hot water according to the manufacturer's instructions. Apply the solution to the stained wood using a brush, let it sit for the recommended time (usually 10-20 minutes), then rinse thoroughly with water. Allow the wood to dry completely before refinishing.

Can it damage wood?

When used correctly, oxalic acid is safe to use on wood and should not cause any damage. However, excessive use, incorrect dilution, or prolonged exposure can potentially lead to the wood becoming discoloured, weakened, or damaged. Always follow the manufacturer's instructions for proper dilution and application to minimise the risk of damage.

Will it remove all types of stains from wood?

It is particularly effective at removing stains caused by water and rust. It also can be very effective at removing the other stains as mentioned above, but it’s not guaranteed to work. You may need to seek professional help with removing stubborn stains and marks 

Can I use it on all types of wood?

It can be used on most types of wood; however, it is most effective on woods with high tannin content, such as oak, teak, walnut, or mahogany. On woods with low tannin content, the bleaching effect might not be as pronounced. It's essential to test the oxalic acid solution on a small, inconspicuous area of the wood before applying it to the entire surface to ensure that the desired effect is achieved and to avoid potential damage.

Common misconceptions about oxalic acid in terms of its use in restoration

Oxalic acid is a universal stain remover:

While oxalic acid is effective at removing certain types of stains, such as those caused by water and rust, it is not a universal stain remover. It may not effectively remove 100% of other types of stains, such as grease, ink, or dye, but in our experience it certainly does greatly lessen them. Some stubborn stains may require specific cleaning methods or more aggressive professional wood bleaches.

Oxalic acid can bleach any wood type evenly:

Oxalic acid is more effective at bleaching woods with high tannin content, such as oak, teak, walnut, or mahogany. Its bleaching effect may not be as pronounced on woods with low tannin content. Therefore, it's essential to test the oxalic acid solution on a small, inconspicuous area of the wood before applying it to the entire surface to ensure the desired effect is achieved.

Will it restore colour to sun-faded bare wood:

Oxalic acid primarily works on stains caused by water, rust, or tannins and may not be so effective in restoring the colour of wood that has been faded due to sun exposure.
However, saying this, again in our experience we have often found it to be very effective at restoring the natural colour of the timber. Sun-faded furniture and wood often requires a combination of actions, such as sanding, treating with oxalic and refinishing. 

Can I use it as a wood finish:

Oxalic acid is a cleaning and bleaching agent, not a wood finish. It can help remove stains and revive the natural colour of the wood, but it does not provide any protection or enhancement to the wood's appearance. After using oxalic acid, the wood should be rinsed, dried, sanded and refinished with an appropriate wood finish to provide protection and enhance its appearance.

Oxalic acid is harmless:

Oxalic acid is a potentially harmful substance if not handled correctly. It can cause skin irritation, eye damage, and respiratory problems if inhaled. It is crucial to take safety precautions when working with oxalic acid, such as wearing gloves, goggles, and a dust mask. Always follow the manufacturer's instructions for proper dilution, application, and disposal.

Is it the best stain remover for wood?

Oxalic acid is considered one of the best stain removers for wood due to its effectiveness in removing specific types of stains, such as those caused by water, rust, and tannins. Its benefits include:

Targeted stain removal: Oxalic acid has a unique ability to dissolve and remove iron and tannin stains from wood. This makes it particularly effective for treating black or dark stains caused by water, metal, or high tannin content in the wood.

Wood colour restoration: Oxalic acid can often help restore the wood's natural colour by neutralising the compounds responsible for the staining and pulling the natural wood colour to the surface. This makes it a very useful tool for preparing wood surfaces for refinishing and enhancing its natural appearance.

Compatibility with various wood types: Oxalic acid can be used on a wide range of wood types, although its effectiveness may vary depending on the wood's tannin content. It is especially effective on woods with high tannin content, such as oak, teak, walnut, or mahogany.

However, it's essential to note that oxalic acid is not universally effective on all types of stains, and it is not necessarily more eco-friendly than other options. Here are some points to consider:

  • Limited effectiveness: Oxalic acid is not as effective at removing stains caused by grease, ink, or dye. Different stain types require specific cleaning methods or  specialised, professional wood bleaches.
  • Environmental impact: Although oxalic acid is a naturally occurring compound, it can be harmful to the environment if not used and disposed of correctly. Large quantities of oxalic acid can be toxic to aquatic life and can harm vegetation if it enters waterways or soil. It is crucial to follow the manufacturer's instructions for proper dilution, application, and disposal to minimise environmental impact.
  • Safety concerns: Oxalic acid can be harmful to humans if ingested, inhaled, or if it comes in contact with the skin. When working with oxalic acid, it's essential to take safety precautions, such as wearing gloves, goggles, and a dust mask, to minimise health risks.

In summary, oxalic acid is highly effective at removing specific types of stains from bare wood, but it is not universally effective.

Customer Reviews

Based on 31 reviews
Reseigh (Hayle, GB)
worked a treat

Beautifully packaged. With a hand written personal note too.
And the product worked brilliantly. Really pleased. Thank you.

Martin Powell (Pudsey, GB)
Starve The Lizards!!!

I was a little bit sceptical with a relatively dilute solution tbh, but how wrong I was. Trying to lift a stain of unknown origin (so not known f it was fat-based or what exactly) out of an internal door prior to varnishing. Only had the stiuff on there 30 seconds tops, prior to neutralising - took the stain and a good bit of the original stain with it, but MUCH better than previous.
Now onto my solid maple kitchen worktops.
Use with some caution ;)

Michaella Allen (Stockport, GB)
Worked perfectly

After an old cake tin had left a great dirty black mark on my oak worktop, I had resigned myself to the heartbreaking fact that it was ruined. As a last resort I took to Google and oxalic acid seemed to be a possible solution, after failing to find this from other retail suppliers I found just what wanted from Gilboys. Alongside the amazing transformation of my ruined worktop, I have never had such a wonderful and thoughtful buying experience. Great communication and I was delighted by the packaging, the hand written note and the wonderful surprise of sunflower 🌻 seeds for my garden, it really made my day, thank you so much!

Kyle Creary-Allen (Lambeth, GB)
Oxalic Acid

Great product, fast shipping. Excellent customer service. Hand written message is a very kind gesture. Will definitely be using again. Highly recommend

Tim Hunt (Reading, GB)
Great product

Great product. Does the job

James (Leyton, GB)

Very fast post, a lovely personal message and some sunflower seeds included. Thank you so much. I planted them straight away.

Kirsty Ruffell (Auckland, NZ)

Excellent product very fast international delivery. I am pleased with the product iI ordered. Highly recommend Gillboys products to others, great company to deal with. Thank you Gillboys!

Dave Crewe (Washington, GB)
Brilliant Service from these guys !!!!!!!!! Definitely coming back to them again.

Very Helpful and quick service and I will be coming back to them in the near future.

Customer in London (London, GB)
Great service

We received our product in good time, and with a personalised note which was really nice. It's worked well for us.

AN (Stroud, GB)
Excellent Company

Good service, and order received promptly. Brilliant product - we got the Oxalic Acid to remove tannin stains from a car port and porch we’ve just had built, and it works a treat! Highly recommend!