“cracked glass”

“I wanted to post an update, as we had a little problem with our new clock. I just noticed the other day that the glass is cracked on the bottom, and I'm certain that it wasn't when I unpacked it and hung it. It never fell off the wall. Our only conclusion is that the metal contracted during one of the deep cold spells this winter, as I hung it on an exterior facing wall, and when it shrank, it cracked the glass. The light has to catch it just right to notice it, so we can live with it like this. However, I would advise you not to hang the clock where it might get too cold.”