This piece of Nakayama Asagi is about 3.0 x 4.0” and it’s a good barber-hone size finisher or touch up stone. But - it has a thin white line showing on the top that looks like the Grand Canyon here but it can’t be felt when honing.
Objective – Neo Splan 5x
Relay lens – 3.3x
Illumination – Reflected Darkfield Off-Axis Fiber-Optic
In the image below, you can see the line as it looks to the unaided eye.
