This is a view of the old part of the Royal Scottish Museum, and you can see how dirty the facade is. Many buildings in Edinburgh from the Georgian era are made of sandstone, which has blackened over the centuries from coal dust and burnt fossil fuels. Amazingly, the oily deposits actually help preserve the sandstone. Buildings that have been scrubbed clean are apparently far more likely to suffer from rot and ruin some twenty years down the line. Photo 4 of 17 in Scotland: Day 1 by Aaron Britt

Scotland: Day 1

4 of 17

This is a view of the old part of the Royal Scottish Museum, and you can see how dirty the facade is. Many buildings in Edinburgh from the Georgian era are made of sandstone, which has blackened over the centuries from coal dust and burnt fossil fuels. Amazingly, the oily deposits actually help preserve the sandstone. Buildings that have been scrubbed clean are apparently far more likely to suffer from rot and ruin some twenty years down the line.