Using Yogurt to Grow Moss on Terra Cotta Pots?

I loved all of your suggestions on how to age my terra cotta pots for my new herb garden! I did the one using lime and had great results, then tried the yogurt/moss technique and followed the instructions exactly. It's been four days now, and instead of moss, all that seems to be growing is black fuzzy mold. What went wrong? Has anyone else had this happen?

By Becki A.