20 30 100differential aids firedtemperature when pore none none noneunder above forming agentcondition fired max u00b0 c crack generating rate 0 0 55interior melts generating rate 0 0 0 difference in bores in out 0 5 1 0 0 5product u03bc evaluation u25ef u25ef x______________________________________ as is evaluated from table 1 in the case that the oxygen concentration in the furnace atmosphere is not controlled as in the conventional manner it is found that the differential temperature between the interior and the exterior of the molded shaped article turned to be a negative value in the range of temperatures from 200 u00b0 to 300 u00b0 c owing to heat generated from the fired molding aids and that its absolute differential temperature was as large as 100 u00b0 c maximum in contrast however with the samples nos 1 and 2 processed with the oxygen concentration of 10 in that range of temperatures according to the present invention it is noted that the negative range of temperatures were from 200 u00b0 to 400 u00b0 c and from 150 u00b0 to 350 u00b0 c respectively and also its absolute differential temperature was as small as 20 u00b0 c and 30 u00b0 c maximum respectively from the visual check up of thus fired products processed under such conditions for the crack generation rate the interior melt generation rate and the difference in bores formed in the interior and the exterior of the products u03bc it was observed that.