The term 'kinko' refers to 'gold worker' or jeweler as is often used for sword furniture as an art form. One can recognize these items by the used metals such as gold, silver and (high noble metal) alloys such as shakudo and shibuichi.
The golden age of kinko was in definitely in Edo period, where the unusual long period of peace allowed craftsmen to hone their skills, often resulting in astonishing but sometimes also unpractical art pieces.
A very nice example is the following koshirae. Especially interesting is the 'ireko saya' (sleeved saya) where the saya is equipped with an 'inner saya' for easy inner cleaning or the saya itself. Practical for the collector, not so much for the samurai :)
Ireko saya are extremely rare and are mostly found on top quality koshirae. More information about the workings can be found on John Tirado's website www.sayashi.com