Recently,spark-plasma-sintering(SPS)technique has widely been utilized to fabricate transparent ceramics.As compared with HIPed ceramics,however,the transmission of the SPSed ceramics seems to be limited,particularly in the visible range.The limited transmission is likely to be related to the discoloration caused by carbon contamination and/or oxygen vacancies during SPS processing.The present study was therefore performed to examine the effects of the discoloration on the transmission.In order to examine the effects of carbon contamination,transparent spinel was characterized on the basis of spectroscopic techniques.