To make coating properties of an entirety uniform with high coating properties by specifying a ratio of a dihydrate gypsum to a hemihydrate gypsum as a material for a mold to be used for molding or the like of an unbaked molding for a pottery product and adding the dihydrate gypsum.

In the case an adding amount of a dihydrate gypsum to 100 wt.% of a hemihydrate gypsum is less than 0.1 wt.%, there is a fear of obtaining no effect of coating properties and uniformity. Meanwhile, a viscosity of a gypsum slurry manufactured by adding water to a material for molding a gypsum mold is increased with a time. The dihydrate gypsum has an action of accelerating an increasing velocity of the viscosity of the slurry. When an adding amount of the dihydrate gypsum exceeds 3 wt.%, there is a fear of impossibility of casting the slurry in the mold so as to spread the slurry to the overall mold due to an acceleration of the increasing velocity of the viscosity of the slurry. For example, in the case of using a material obtained by adding 0.5 wt.% of dihydrate gypsum to 100 wt.% of the hemihydrate gypsum, a gypsum mold having 65% or more of a mixed water amount and a range of 0.015 to 0.035 cm2/sec of a diffusion coefficient can be obtained.