Double casting method (cast on technique) is sometimes used for attachment work. As to this method, the present study was conducted to investigate the partial deformation of casting and the castability of the second casting. A wax sheet stuck on the first cast plate of a gold alloy was invested with a gypsum-bonded investment. Using a centrifugal casting machine, two kinds of alloy were cast in the mold heated to 700°C: one was the same alloy as the first casting and the other was a silver-palladium-gold alloy.
Protuberances on the first casting and the corresponding concaves on the second casting were found approximately beneath the sprue. Some protuberances appeared to be wavy, while the others appeared to be hemispherical, with a maximum height of 220μm. There were no differences in the size and shape of crystal grain as well as the composition between the protuberance and the body of the first casting. Therefore, the protuberances did not result from the adhesion of the molten metal to the first casting, but from the partial deformation of the first casting. In case of using a silver-palladium-gold alloy for the second casting, some of the first castings had concavities.
The castability of the second casting was significantly low, compared with general casting.