Dull spots can quickly happen if you use the wrong type of cleaner or certain spills are left. Acidic stains such as red wine, coffee, and soda, or alkaline stains like olive oil and green tea can also cause dullness.
These can cause dullness even if you clean the spill right away with water and a mild detergent. Luckily, you can restore the glossy surface using a polishing powder specialized for marble.