Spectroscopic techniques have been used to identify oxidation states in manufactured pieces for some time. Light used as a signal is potentially more reliable since it is not prone in the same way, to interferences that can affect electrical signals. While using light at low temperature has been common practice, the emissivity of glasses at high temperature has restricted its use. Absorbance spectroscopy is the commonly used method. However, reasonable concentrations of absorbing species are required for identification, which quantitatively depends on the geometry of the sample. Optical absorption measurements for glass samples from ambient temperatures up to 1300 deg C have been made. The ferrous band at 1050nm was the only species measured, and therefor the ferric/ferrous ratio could not be determined with changing temperature.
