Thread: Slurry Edge Dulling, Convexing and Micro Chipping

Slurry Edge Dulling, Convexing and Micro Chipping

There has always been an on-going discussion about slurry and edge dulling vs sharpening. And the art of creating, and use of slurry for cutting vs polishing.

The “Art” part is the ability, to read slurry and creation for a specific use, cutting and or polishing, (they can be very different), thick/thin, Diamond vs Tomo slurry or other slurries.

The old school, of creating a thick slurry and thinning to clear water has always produce mixed results, hence the mystery and Art. But why?

Recently, I viewed the Micro Graphs of swarf posted, on the Science of Sharp website, in the (Swarf post).

It was interesting to see the shape and size of swarf at magnification, but makes a lot of sense. Based on what we see from grading body filler, probably the most graphic example of a similar process in a larger scale the metal swarf is shaped in curly cues, almost like micro springs, where metal is scraped from the bevel to form a groove/stria by the grit of the stone.

This post, also is in keeping with Alex Gilmore’s theory and post (on honing on slurry and swarf and search for the cause of edge blunting), on his site, and his findings on, making a bur intentionally, then removing it to, re-set and make a solid v shaped edge, (the japanblade.com/blog), (Why Develop a False Edge on Purpose?)

Alex theorizes about a wave of thick slurry, forming at and under the edge, in an edge leading stroke. The aggressive cutting power of thick slurry can convex the very edge by aggressively honing at the edge. The results can be the edge worn and micro convexed.

But added to Alex’s observation, is swarf. In effect the edge is hydroplaning on slurry and the rounded (springs) of swarf. Especially if light pressure is used in the final laps, while using the same slurry, the edge can become both convexed and damaged, (Micro-chipped).

While the conventional, theory for the slurring naturals, has been to break down the slurry, with repetitive strokes, there is a fine line where the slurry is getting finer, swarf is added to the slurry, and the edge burr/fin lengthens, further impacting the edge and convexing the very edge and possibly weakening the edge.

When, then a clear water honing is performed, with light finishing strokes, the edge is not in contact with the stone, and may be damaged by the swarf and can fracture and micro-chip and not touch the stone.

A lot is going on at the edge, of a slurry honed, edge leading stroke, none of which we can observe, in real time.

While slurry thinning, and working with repetitive laps, will break down some slurry, there is a point of minimal return, where breakdown is maxed, addition of swarf is detrimental to the edge and additionally, the fin is lengthened, especially with large number of laps and not re-newing the slurry.

Alex recommends fewer laps and making new slurry to keep the cutting power of the slurry maximized, (and free of contaminants, swarf). Of course, knowing your slurry, how aggressive it is and how quickly it breaks down and feeling, when cutting is minimized, is literally in the hands of the honer and formulaic honing goes out the window, as it should.

What are your thoughts on these two theories and the combined effect on the edge, and what is your experience?


Sorry forgot to link the two post in question.