polishing process; glazing process
A finishing process that imparts a glossy, lustrous surface to materials such as ceramics, metal, or wood.
This pottery has a beautiful luster from the glazing process.
Metal parts that have undergone a polishing process have a luxurious feel.
研磨 is a general term for grinding or polishing, while 艶出し加工 specifically refers to a process aimed at producing a glossy finish.
光沢仕上げ is a near-synonym also meaning glossy finish, but 艶出し加工 is more commonly used in industrial and manufacturing contexts.
Compound of 艶出し (tsuyadashi, 'bringing out luster') + 加工 (kakō, 'processing'). The exact historical derivation is uncertain, but the term is transparently formed from its components.