Apply with a prop or cloth disc to polish limestone.
For wood:
Oxalic acid is also suitable for removing black circles and other discolourations from wood, for removing rust, for descaling ships or for other applications you have found.
We use oxalic acid, also called design water or weather stain cleaner, on wood to remove black circles or other discolouration as follows:
- Dissolve about 100 grams of oxalic acid crystals in one litre of water. Hot water is the fastest; for cold water, let the solution sit for a day and shake occasionally.
- Apply the oxalic acid to the circle with a brush and let it soak in.
- If necessary, repeat the oxalic acid treatment until the black discolouration has disappeared.
- If the circle / spot has disappeared, it may have been replaced by a bright spot.
- Now treat the entire surface (not just the circle / stain) with the oxalic acid and let it soak in again.
- Finally, rinse well with clean water to neutralise the oxalic acid.
- Let it dry and treat the surface further, for example with Stone Wax or Stone Wax Pro, these are also very good for wood.