Marble is a relatively soft and sensitive stone that can be easily damaged if you put acid on it. Common acids that can damage your marble are citrus juices, vinegar or wine. Avoid using these substances around marble. If you've spilt these items on the marble and it's been etched (small scratches that damage its lustre and shine), you'll have to polish out the acid damage. Polishing powder, which is mildly abrasive, will wear down the marble around the scratches to restore an even surface.
Add a few drops of liquid dish soap to a cup of lukewarm water. Mix until suds begin to develop.
Dip a sponge into the soapy mixture and rub the walls of the shower. This will remove all of the soap scum and hard water stains from the marble shower walls.
Rinse the walls with clear water.
Gently sand the acid damaged shower wall with coarse wet/dry sandpaper. This will smooth out the etch marks. Use wet/dry sandpaper because it will not get clogged with sawdust. Sprinkle the marble walls with water once you notice that they're getting drier.
Gently sand the acid damaged shower wall with 320-grit wet/dry sandpaper. This will blend the etch marks and make the marble appear smoother.
Gently sand the area with 600-grit wet/dry sandpaper. This will ensure that the shower is as smooth and soft as possible.
Make a paste of polishing powder and water according to the manufacturer's instructions. The paste should be the same consistency as thick frosting.
Apply the polishing paste to the area with a clean cloth. Rub the cloth in circular motions until the marble appears smooth and the area is blended with the rest of the marble.
Rinse the area and dry it completely with a clean cloth.