Richard alerted me that you were discussing my photo of Emily Watrous's dad's boots. I will post two other photos. One a slightly closer stereo view and the other, an extreme closeup.
I know imprecisely the history of these boots. They were in Emily's dad's backyard somewhere in the Shohomish River valley (up along Rt. 2 east of Everett, WA) for a great many years (more than 10). If Emily is still living over where she was 2 1/2 years ago, I will attempt to find out more information AND, if the boots are still on the front stoop, get a new photo to see if there is any additional growth. Of course, we all know that lichen growth is very site-specific, so any growth in Bellingham would not necessarily correspond to growth in the Snohomish valley. But it would be a start.