The view above is common in Tokyo: rough, old and weathered giant stone block walls. Images of ninja scrambling along them... er I digress.
Walking back to Shibuya from Harajuku a few weeks back, I noticed this wall:
Obviously, some recent repair work had been done and a section of the wall renewed. However, I wondered why these new blocks were so dirty, and the older ones not? There was no puddle of mud on the road that could have splattered, even if so perfectly avoiding the old wall, onto them.
Upon closer inspection:
What is that? Why is there so much crap splattered over all these... oh wait a minute. This isn't dirt splatter; this is half rotten wood! Half rotten wood chips IN the concrete blocks!
Wood chips are mixed into the concrete blocks. Over time, with humidity and rain and temperature changes, the wood expands and contracts and accelerate surface erosion of the concrete blocks, giving them a nice, ancient, weathered rock look and feel, probably within a few months.
How great is that? It's a good thingTM