Black coal smoke has wafted out of about 200 iron foundries near the Taj Mahal for years, slowly turning the building's white marble to yellow.

Now scientists hope to save the darkening mausoleum with a new type of furnace design that will help the foundries cut emissions, the government's top research organization said Tuesday.Tests showed that redesigned furnaces using natural gas instead of coal drastically cut toxic emissions, said director-general of the Council for Scientific and Industrial Research, R.A. Mashelkar.

In recent years, the Supreme Court has issued a series of orders ranging from moving the foundries out of the area to planting more trees to combat pollution in Agra, the city where the Taj Mahal is located.

Experts say the marble has been stained by pollution and its stones have been chipped, but the 17th century building is structurally sound.