The GC Nagura is a synthetic auxiliary stone made of Green Carbon (green silicon carbide) designed to maintain and optimize fine sharpening stones, typically from #3000 grit. It cleans the stone's surface, creates a homogeneous abrasive slurry, and improves the finishing quality.

Compact and easy to use, it revives the abrasive power of finishing stones and promotes more consistent and precise sharpening. To preserve its performance, it is recommended not to leave it constantly immersed, as prolonged soaking can soften it.