The quality of ceramics product is greatly affected by the mixed and dispersed state of materials. Mixture of hemihydrate gypsum and copper oxide was prepared by dry and wet process, and the cross section of its sintered body was observed to quantitatively evaluate the mixed state by using image analysis. The values of standard deviation of the area occupation ratio of dispersed particles (copper oxide) were measured from 10 independent observation of the four different size of area, which was expressed as (1/2) N·A, where N is the divided dimension and A is the area whose size was about 1000 times of primary particle diameter. The values of standard deviation for different size of areas were constant below the critical dimension (Nc), but those were significantly deviated at the range of N greater than the Nc. The definition of the degree of mixing is proposed in terms of this Nc, whose values are in the range of 0 to 10. Mixing speed can be evaluated quantitatively by using with this degree of mixing. The rate of wet process was 5.4 times faster than that of dry process.
