Enigmatic!
Some time back I purchased a Chinese Hone rated as 15,000 grit. I had not used it, and happily so, when I discovered that one should check the flatness of their hones. Fortunately for me I possessed an engineers straight edge (used it to assure the flatness of an engine block and head for a proper fit). I laid the straight edge down on the Chinese hone--parallel to the long edge of the stone and noted that either end displayed light indicating that the central part of the stone was not flat, but rather convex. I contemplated the purchase of a flattening hone but opted for my table belt sander. With the straight edge, and patients, I finally achieve what I believe to be a perfectly flat "Chinese" 15,000 grit stone. The opposite side was the opposite. The edges were high creating a bowl like center. The process of eliminating the bowl center took as much caution and patients as the opposite side but with time and patients the bowl was eliminated and I created a hone "engineer level" flat.
The ease with which the stone was removed makes me wonder if the hone is truly a 15,000 grit. Since the stone was inexpensive the belt sander worked fine despite the finish using a 400 grit sand paper on a flat granite surface.
Anyone ever have the occasion to flatten a hone? How did you do it? How long did it take? What are your suggestions?