1. Mild cleaner: Use mild cleaner and soft cloth to gently wipe the area affected by black stains. Choose a non-corrosive and low-acid cleaner, such as mild soapy water or diluted detergent.

2. Lemon juice or white vinegar: Apply lemon juice or white vinegar to the contaminated area and gently wipe it with a soft cloth. These acidic substances help to remove stains, but be careful when using metal surfaces to avoid excessive use or long wiping time.

3. Eraser: Try to gently wipe off the black stain with a clean eraser. The rubbing action of the eraser helps to remove some surface stains.

4. Professional cleaner: None of the above methods can remove the black color of the golden seal. You can consider using a professional metal cleaner, choose a metal cleaner suitable for ancient gold seal and use it according to the instructions. Steel seal is a seal made of steel plate engraved with two seals: upper and lower yin and yang. It is covered on special documents or photos, with no color, only raised words, numbers and icons.