In my brother's head for example. (he's an engineer in a hone factory)
He made me two (different grits) that are quite allright.
Buddel has one of them (the coarser one) and I got some more here now.

He said its a very old recipe they used to manufacture for Solingen.
Reminds me a lot of my Tojiro 4000 in a many aspects.
The cracks for example, the milk and the sound when you knock on it as well.
Cuts fast, but not too coarse. Good for restos.