These marble lamps have yellowed over the years. (Reader photo/Reader photo)

Q: I gave two marble lamps to my grandmother as a gift many years ago. They were white marble then but are yellow now. My grandmother was a heavy smoker, and I assume the nicotine contributed to the discoloration. I was given these lamps after she died, and I want to restore them to their original condition. How can I get the marble back to white?

Bethesda

A: Nicotine residue does stain marble, so there's a good chance the yellowing was indeed caused by your grandmother's smoking. But from the picture you sent, the surface looks glossy and the yellowing might also be aging of a coating, said Constance Stromberg, a professional conservator in Bethesda whose specialties include dealing with decorative items made of stone (301-263-9298; c.stromberg@verizon.net). There is also a chance that the lamps aren't marble but instead are alabaster, a softer stone that often looks almost translucent; or Ivoreen, a cast and filled resin made to look like marble, she said in an email.

Methods for cleaning marble might damage surfaces that aren't marble. For example, if you try to clean alabaster by wiping it with a cloth, especially a moist one, you are likely to drive grime into the stone rather than remove it. So if you aren't sure what you're dealing with, consider getting advice from a trained conservator. The American Institute for Conservation of Historic and Artistic Works offers a "find a conservator" service, searchable by Zip code and specialty, on its website, conservation-us.org .

But because you bought the lamps originally, if you are confident that they are bare marble, you might test one of these cleaning procedures in an inconspicuous area and then proceed with what works best.

Stromberg's suggestion: Clean with a cotton swab dampened with ammonia diluted in distilled water to a concentration of approximately 3 percent. Janitorial ammonia is 10 percent strength ($2.79 a quart at Ace Hardware, acehardware.com), so if you start with that, mix 1 cup from the bottle with 2 cups of distilled water.

The Victoria and Albert Museum in London's advice: Clean with a non-ionic detergent diluted in distilled water to 2 percent concentration or less. Simple Green All-Purpose Cleaner ($2.29 a bottle at Home Depot, homedepot.com) and many kinds of dishwashing liquid are non-ionic detergents, which mean they have a neutral pH and are particularly efficient at removing grease and oil. There are 48 teaspoons in a cup, so, at most, use 1 teaspoon of detergent per cup of distilled water.

It's important to work quickly, said John Teymourian, part owner of Artisan Lamp (202-244-8900; artisanlamp.com), a store in Washington that specializes in vintage fixtures and often cleans marble lamp bases using the detergent regimen. Immediately rinse off all residue, not by directing a gush of water onto your lamps but by dabbing and blotting with a clean cloth, he said. Teymourian recommended following up by applying a marble wax after the surface dries.