Porcelain composition, porcelain and method of producing the same, and wiring board and method of producing the same

The porcelain of the present invention comprises 5 to 70% by weight of a non-oxide ceramic filler and 30 to 95% by weight of a borosilicate glass having a glass transition temperature of 800° C. or lower, wherein a weight loss per unit surface area of said non-oxide ceramics is not more than 0.15 g/cm after dipping said non-oxide ceramic having purity of not less than 96% by weight for five minutes in a glass melt obtained by melting said borosilicate glass with heating at 1200° C. Since the porcelain composition can be fired at a low temperature together with a low-resistance metal, the resulting porcelain has a high thermal conductivity, a low dielectric constant, a high heat dissipation property and a reduced apparent signal delay in a high frequency signal and is suited for use as an insulating board in a wiring board.