Rob asks TPP: I like to make picture frames from old barn wood. I recently acquired some wood that has lichen on it and thought it would be cool to have some on the frame but do not know whether or not it would be harmful to humans in a household environment. Also if it isn't I would assume it would maybe dry up and just crumble off or disintegrate or would not last. Any ideas on this. I do not know the name of this lichen, I live in West Central Minnesota and see it all over the granite outcrops, roofs of house, on trees and wood. Thanks for any help.
In answer to your questions: Lichens are not harmful to humans in a household environment. However humans can be quite harmful to lichens; in urban areas they can be the canaries in the coal mine type of indicators of air quality (they don't like pollution). Depending upon the lichen, they would just desiccate and could last on the wood for a considerable period of time, especially crusty lichens. They actually make "living walls" of lichen-covered bark or wood, but your living picture frames would require some occasional moisture (not good for the pictures) and some light, although not necessarily much of either. TPP doesn't know the name of your lichen either having never seen it. On the diverse substrates you mention, there would be multiple kinds of lichens. There is a nice book called Lichens of North America, it has an identification key, but it's rather technical; all the wonderful pictures might prove more useful. Maybe a local university library will have a copy. It's a big book. The image shows several lichens on an old birdfeeder in the Smokey Mountains of North Carolina, so yours would be different.
Kurt Gödel's Open World
14 hours ago in The Curious Wavefunction