How best to clean a marble hearth?

Go to home depot, in the tile aisle there is a series of products called Miracle. They come in a blue bottle. One is a specialty Marble Cleaner. I forget how much it costs, but that is going to be the best thing. Also, if you haven't sealed the marble, get the Miracle marble sealer, "511 impregnator" and seal it well.

You don't want to get a real harsh abrasive cleaner because you will ruin the marble. (This includes some of the products people have suggested above) Only use specialty products on marble, you don't ever want to guess that something is ok. Marble is such a "tempermental" stone.

For heaven's sake DON'T use any acid. That includes vinegar, citric acid, lemon juice, muriatic acid, spirits of salts, hydrochloric acid, battery acid, etc. These dissolve marble and your fireplace will lose any polish it has. Moreover acids don't attack grime very well.

You CAN use alkaline cleaners, I have found that marble objects soaked in a mixture of laundry detergent powder and water for several days come up clean. This is probably not practical with your fireplace unless you can take it apart and have big enough containers for the parts.

In the absence of a proprietary marble cleaner, try scrubbing, soft brush, with a sludge of laundry detergent powder in water. This will be hard on the hands so wear gloves. Leave the detergent sludge on for a while, maybe an old wet towel over it to keep things damp as long as possible and repeat as required. You can also try "sugar soap" which is a highly alkaline soap/detergent or maybe it's called "lye soap" where you live.

Marble is a very soft rock and is very porous, so do not apply any highly coloured material or you will have to get that out as well. Unfortunately years of smoke and soot will have been absorbed by the marble and it may never be "as new" clean.

1

Spray it with WD.40 then wipe, it works a treat on my slate hearth (beware as it's flammable, so use it when the fire's out)

Vinegar diluted with wam water and a soft cloth

Lowe's or Home Depot has cleaner cream for marble.

Works well.

Just a damp cloth.

with a tissue

baking soda and water