Cleaning marble sink
Regularly clean your marble with a mild dish detergent or cleaner specifically meant for stone or marble. This can be purchased at a local hardware store. Apply a small amount of cleaner to a soft cloth and rub evenly over the marble. Thoroughly rinse with water. Completely dry with a cloth afterward to prevent water from seeping into the marble or water spots from forming on the surface.
Maintenance
Wipe up spills on the marble immediately. Because of the porous nature of marble, it will absorb liquid and possibly could form a permanent stain. Once water spots or stains appear on the surface, they are difficult to remove, but not impossible. Do not allow mineral deposits such as iron, salt, lime, or soap to build up on your sink as this will dull the finish and possibly stain the marble.
Sealing/Polishing Marble
Polish your marble sink by hand occasionally with a product specifically designed for marble, which can be purchased at any hardware store. Just use a soft cloth or pad, and polish evenly over the entire surface to keep your marble sink looking shiny and new. Use a sealer on your sink at least once a year, which will help deter elements from seeping into it. The lifespan of marble sinks that are not sealed will be greatly diminished compared to those whose surfaces have been sealed.
Considerations
Do not use acidic products or abrasive cleaners on the marble, such as ammonia, vinegar, alcohol, window cleaners or lemon juice as these can cause permanent etching on the surface and can eat away at the marble.
When exposed to acidic materials such as orange juice, the pores in the marble open up, and the marble becomes more absorbent.
In addition, avoid using abrasive scouring pads such as steel wool or metal brushes as these could also scratch the marble surface.
If water rings form on the marble, it may be best to have the sink re-polished by a professional to help remove them.