Diesel Patina

On a walk through the park I encountered council workers who'd just replaced a couple of slats on a black bench. They laughed when I asked them if it would have been easier to stain the wood before it was nailed down. They explained the air pollution quickly stained the wood black.

"It's environmentally friendly, innit?" asked one of the workers. "You wouldn't believe the shite that's in them stains."