Abstract—A comparison of the effect on mold filling of using vacuum vs. a protective gas of Ar during casting has been carried Out. A conventional gold casting alloy and a NiCr‐alloy without Be have been cast at three temperatures into two different mold patterns: a mesh screen and a cylindrical crown with a 30° sharp margin. In all cases the application of vacuum rather than a protective gas of Ar was found to be beneficial for the mold filling. A reduction of the back pressure due to the trapped gases in the last part of the mold to be filled with metal was assumed to be the major reason for this effect. A reduced surface tension of the melt may also contribute. An improved mold filling was also observed for both nets and crown margins with increasing supertemperature of the melt. Physical reasons for this effect have been sugge