They are good photos. They clearly show the obvious difference between white blobs and lichen. Also does lichen grow on all surfaces or is one type of stonework more prone than others?
This morning, near a tube station on my way to work I found a blob "work in progress".
There were several dark "old'uns", one which had spread smooth - with a dark outline or damp patch, a couple which had started to brown and a fresh lump, still with teethmarks. I shall of course attempt to photograph this cluster and, in a scientific but sad way, try to study it's progress.
Naturally, I'm going to find it tricky to explain to my workmates who already consider me dangerously odd since my knuckles don't drag along the ground and I read for amusement rather than necessity.