I can definitely see why. In Rome you can see 2000-year-old buildings covered in soot. It's heartbreaking to see what 50 years have done to such illustrious landmarks. They can be cleaned through sandblasting, but that process damages stone further. Most historic buildings in DC are covered in porous marble, am I correct?

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[GONE] - 1995 Mercedes E300 Diesel - 130k miles - Smoke Silver (702) over Mushroom leather (265) - Bladder blasting, coast-to-coast work machine.