Pittsburgh used to be a city of massive black stone buildings, but, since the end of the age of steel, the buildings have been cleaned one by one, revealing the actual color of the stones as they came out of the quarry. Few of the black stone buildings are left. Here is one of them: Fourth Presbyterian in Friendship. Over the years, the stones are gradually losing their sooty coating, revealing what looks like red sandstone underneath. But they are still strikingly black, the way all proper Pittsburgh stones used to be.