What treatment process would be used to achieve a shiny surface finish on metal?

Achieving a shiny surface finish on metal is primarily accomplished through the polishing process. Polishing involves the use of abrasives or polishing compounds to smooth and refine the surface, effectively removing imperfections and enhancing the reflectivity of the metal. This process can be done manually or with machines, and it is essential in industries where aesthetic appearance and smoothness are critical, such as jewelry, automotive parts, and home appliances.

In contrast, hardening refers to strengthening metal through heat treatment but does not directly contribute to surface appearance. Aging is a treatment that alters the microstructure of metals to improve properties like strength and toughness, but it does not focus on refining the surface. Quenching is a rapid cooling process often used after heating to set certain properties in metals, usually resulting in increased hardness, but it does not have an impact on creating a shiny surface finish. Thus, polishing stands out as the correct technique for achieving that desired aesthetic quality.