Marble provides a durable fireplace trim and a traditional, timeless appearance. Marble is a soft, porous stone and over time will become grimy and grey because of the smoke and soot that fireplaces emit. Although many consider ageing marble beautiful, there are several steps you can take to ensure your marble doesn't look dingy and dirty.
Mix 1 qt. of warm water and 1 tsp of dish washing liquid in a bucket. Dampen a soft cloth with the mixture and then use it to wash the marble. If the marble is very dirty, you may need to use a soft-bristled brush to clean it. Rinse with clear water. This should remove the surface dirt, but in most cases you will see sooty stains in the marble and on any grout around the stone.
Measure out 2 tbsp baking soda and ½ tsp lemon juice. Add just enough warm water to make a thin paste. Do not increase the amount of lemon juice, since too much of it can etch and stain the marble. Rub the paste onto any stains on the marble, allow it to sit for about 10 minutes, then rinse with clear water. Dry it with a soft cloth.
If the marble is now less stained than previously, repeat the application in Step 2 until the stain fades as much as possible. If the paste has had no affect on the stain, several commercial marble cleaners containing strong chemicals are available, if desired.
After removing as much of the smoke and soot stain as possible, thoroughly rinse the stone, changing the rinse water often. Dry it using a soft cloth or a chamois so no water marks will appear on the marble.
Use high quality, non-yellowing paste wax, such as furniture wax, beeswax or a marble wax (found in hardware and fireplace stores), to polish the marble. Spread the wax with a soft cloth, wait about 15 minutes and then use a fresh cloth to buff until it is shiny.
Because marble stains and scratches easily, do not use common cleaning agents, such as bleach, vinegar and cleansers.