Here is one of our CD 327s with a flashover. As you can see the carnival coating was blistered away. The rough texture at the top of the mark appears to be metal fused into the glass. The wrinkling you see was caused by the heat and is actually in the surface of underlying glass. Keep in mind this is boro-silicate glass, similar to your glass cookware. We do not know if this was caused by a direct lighting strike or an over voltage from a strike or other source.