PHILADELPHIA -- The Tomb of the Unknown Soldier of the American Revolution has been defaced and the National Park Service states they are coming up with a solution to remove the vandalism. CBS reports the vandalism could be gone in about two weeks.

As stated on Facebook:

Preservation at Work: The National Park Service is working to remove this graffiti on the Tomb of the Unknown Soldier of the American Revolution (at Washington Square) safely. We appreciate the offers to help that we've received, and we ask your patience while professional conservators continue this delicate task. Thank you for your encouragement and support.

The Problem: The wall of the monument is a very soft and porous limestone that's susceptible to pitting and discoloration. To clean this stone without damaging it, we've tried non-abrasive steam cleaning and a gentle solvent. But, some paint on the wall remains.

The Solution: A professional stone conservator is now addressing this graffiti. The treatment saturates the painted stone with a mild solvent held in place by poultices (soft masses). After about two weeks, the stone's appearance should improve.