The Myth Of Fast Cutting Diamond Stones

Often, you hear about sharpening, that the fastest way to remove steel from a knife is to use Diamond plates. This, in fact, is not exactly true. Yes, an XC diamond plate has a coarse grit, and given if it is clean and lubricated, it is an effective sharpening tool. But, compare it to an oil stone, like a Norton Crystolon (SiC) or India ( Al2O3) Stone, freshly conditioned, it is slow cutting. The reason is pressure. You should never use pressure on a Diamond or CBN stone, as it will prematurely wear the stone out. But a Norton Crystolon or India Stone, freshly conditioned, can be used with a lot of pressure, and will remove steel very quickly.

Thank you for saying what I’ve been thinking. I’m very close to relegating diamond stones to the finishing stone realm. They are great for that final edge at whatever grit you choose. They are not great for rebeveling.

I have come to a similar conclusion about diamond plates for sharpening, though I hadn't really thought about it. I was just disappointed in the Atoma 140 for thinning edges.

Diamond plates are often marketed for flattening other stones. Should we consider that maybe a SiC stone for flattening AlO is faster? Or perhaps a steel lapping plate with loose grit?

William,
I guess it depends on what is convenient for you. I have a DMT Black XC stone that I use to recondition my Wayne Goddard Norton M Crystolon (SiC)/Norton F India (AlO) just because it is fast, not messy, and I usually have the DMT stone at the ready. SiC Wet/Dry works, and so does the loose grit. The late great Stefan_Wolf had a bunch of videos of him conditioning his stones, using a few different methods.

I like using loose grit on ceramic pavement slabs, a bit messy but works very well in my experience, readily conditioning and flattening even hard bonded Alox stones like Norton India or spyderco ceramic in a matter of seconds, I use 36 grit Alox blasting grit to flatten and then various grades of Sic, never felt the need to have a proper flattening stone.
That say, I I mainly use vitrified alox and Sic with oil, so your mileage may vary
About the original topic, the few plates I owned over the years always ground fast, but not as fast as an hard, very coarse stone used with pressure, unless you are willing to buy new plates every few thinnings(costly) doesn't feel to me as a sensible use of money.
I pretty much only grind simple steel at moderate hardness, so your mileage may vary also on this

Todd from Science of Sharp showed that diamond plates tend to break carbides and reduce edge durability. Any carbide can be broken by diamonds. Vanadium, Tungsten, Molibdenum, and Vanadium.

Carbide break may cause loss of initial sharpness but not always. Edge may be perfectly formed and only the carbides are broken. When this happens they function as fracture initiation points and reduce edge durability.

This seem to happen quite often but it's not a rule that always applies. If you have good durability with diamond then no need to change.
Maybe I should test this to see how much of an impact it has but I'm laisy on edge retention tests so I tend to just avoid diamonds as finishing stones.

I got two resin bondended Diamond stones. They are quite hard, not the best cutting speed but good enough for light thinning and aesthetics sharpening. After using them I finish with something else to get rid of broken carbides.