If the black stains on the ceramic are caused by mold and cannot be removed with general cleaning methods, you should choose a cleaning product or mildew killer specifically designed for ceramic surfaces and strictly follow the instructions on the label to prevent potential damage to the piece.
Before using any cleaning product, test it on a small, inconspicuous area first to observe whether the cleaning agent affects the color, pattern, or glazed surface of the ceramic. Additionally, wear gloves while cleaning and use in a well-ventilated area.
Caution: Do not mix bleach with vinegar, ammonia, or other cleaning products, as this can produce gases that are harmful to the respiratory system.
For valuable ceramic pieces, artworks, or those with special glazed surfaces, avoid using strong chemicals and consult the manufacturer's instructions before cleaning to help preserve the color, pattern, and surface condition of the piece.