I thought I was joining my husband in his kingdom of Pareidolia when I thought there were mold or trace fossils, which I now know as ichnofossils, on some of my sherds from time to time. I have no idea how long it takes for such fossils to form, and I often don't have a guess as to how old a sherd might be or how long it could have been in the ground or water, but I am changing my mind. I see fossils on my sherds and I'm not crazy (well....)! I hope these examples are photographed well enough for you to see them, too. I'm very curious if this is common and if I can date the sherds according to the fossils.