Cored wire including at least one thermal barrier layer, distinguished by the fact that said layer is made of a material that pyrolizes upon contact with a metal bath such as liquid metal. The device also includes an upstream-side trailing edge detector for detecting a trailing edge of the recording medium, a downstream-side trailing edge detector for detecting the trailing edge of the recording medium, and a skip warning region determination unit for determining whether the trailing edge is located in a skip warning region. The frequency of the periodic signal that caused the null or peak may be used to calculated the length of the transmission line or a propagation delay through the transmission line. The light transmitting discharge layer is useful as a surface coating for visual displays such as CRT screens to avoid electrostatic accumulation of dust and scratching.