Alessandro Porta, representative for Campolonghi, the Italian firm that delivered the marble to the new Opera, does not believe the stone itself is at fault.
"When marble ages it does not yellow, Porta told Aftenposten.no. I have never seen such a color, a strong vital yellow, on marble. Our theory is that it is due to much dampness in the foundation. The marble lies like a lid over this dampness, which forces its way through the stone, because it has nowhere else to go," Porta said.
Porta said that his company was cooperating with research foundation SINTEF to try and solve the problem.
"We know of no similar cases, and our marble is in use all over the world. It is damp in the foundation, and we believe the problem would have occurred with any type of stone, not just marble," Porta said.
Oddvin Fosse, a specialist from the Norwegian Stone Forum who has worked with laying stone for nearly 40 years, agrees with the Italians.
"From the structure I cannot see that there is anything wrong with the stone, though I would have preferred granite. The mortar SINTEF describes should not be a problem either. I am almost completely sure that it is moisture in the concrete that is the problem," Fosse said.
SINTEF researchers said that the hypothesis was a possible and perhaps even likely explanation, but they were carrying out thorough tests. A report is scheduled for December 10.
