The conservation architects I used to live with spoke of soaking bricks in ox blood to get an authentic colour and spreading milk and yoghourt on walls and benches to encourage the growth of mosses and lichens.

Does that even work? There’s only one way to find out. Tho my sister and co-owner says you need to mix in manure for best results. And this web site says you need to throw in some moss and mix it in a kitchen blender (like you keep a spare one for stomach-churning experiments). More to this than meets the eye.