Shorts

The final polish of a cast gold alloy to achieve a smooth polished surface is done by

1) Pickling: This is a process used to remove oxides and impurities from the surface of a metal before applying a final finish. However, it does not provide the final polish.
2) Electropolishing: This technique uses an electrical current to dissolve the metal surface and create a smooth finish, but it is not commonly used for gold alloy restorations.
3) Sandblasting: This method involves propelling an abrasive material against the metal surface to smooth and clean it, but it is too aggressive for the final polish of a gold alloy restoration.
4) Rouge: Rouge is a fine abrasive paste used with a polishing wheel or point to achieve the final polish on a cast gold alloy restoration. It removes minor imperfections and gives a high luster to the metal.

The correct answer is 4) Rouge, as it is the standard technique for achieving a smooth, polished surface on cast gold alloys.