In this study, an attempt was made to mask an inhomogeneous gray colouration featured on the surfaces of the gas pressure sintered alpha-beta SiAlON ceramics containing 50% alpha and 50% beta SiAlONs in the form of spots. For this purpose, tungsten carbide (WC) powder was added to the starting composition in the amounts of 0.25 and 0.5 wt.%. Both a visual examination and L*a*b* measurements with a spectrophotometer showed that 0.5 wt.% WC addition was effective enough in masking the spots completely. The resultant microstructures were investigated using XRD, SEM and TEM techniques in combination with EDX analysis in order to reveal whether the WC addition had an influence on compositional and microstructural development. According to XRD, a W containing phase and alpha-SiAlON and beta-SiAlON were the only crystalline phases present. In addition, electron microscopy results demonstrated that W containing particles were located at the triple junctions and no change in grain morphology was present. (C) 2003 Elsevier B.V. All rights reserved.