When diamond stones are not fine enough, you can finish up with Dia-Paste by DMT. With grits as fine as 1 micron, you can hone an edge to a degree that diamond stones just can't match. 2 grams.
Just put a dab on a flat piece of maple or MDF and use it like you would a sharpening stone for a mirror polish.
Diamond paste is traditionally used to sharpen by applying it to a piece of maple or MDF.
Available in 1, 3, and 6 micron grits. Made in the USA.
DMT Part Numbers
6 micron: DP6
3 micron: DP3
1 micron: DP1
Set of 3 Grits: DPK