This report illustrates a sharpening progression inspired by techniques demonstrated by knife maker Murray Carter in his straight razor honing video:
This series of images is particularly effective in demonstrating the differences between edge leading and edge trailing strokes. A technique for burr removal is also illustrated.
First, a comparison of edge-leading and edge-trailing sharpening on the King 1k stone, starting with edge leading:
Next, edge-trailing. As expected, edge trailing strokes on the King 1k leads to the formation of a foil-burr.
Moving to the King 6k stone, first with edge-leading strokes. The apex micro-chips faster than the bevel is abraded preventing the formation of a burr.
Surprisingly, edge-leading strokes on the 6k stone have reduced the keeness of the apex as compared to edge-leading strokes on the 1k stone in this example. Although the scratch-pattern is finer, this does not correlate to an improvement in keenness. Swarf and loose grit may play a role in this process, as suggested by the second image below.
The above progression was repeated under running water to determine whether continuous flushing of swarf and slurry improves the keenness with achieved with edge-leading strokes on the 6k stone. The image below shows no improvement.
Next, to edge trailing strokes on the 6k stone. Once again, edge trailing strokes lead to the formation and growth of a foil-burr.
The technique described in the embedded video should be expected to produce a standing burr beyond the apex. The next step is to cut into a piece of soft wood several times and observe the effect on the burr. The images demonstrate the result in this example.
The burr above was relatively large and easily folded. The progression was repeated, to create a more subtle burr, shown below.
Cutting into a piece of redwood with the smaller burr also causes it to fold over.
It may have been expected that the burr would be torn off; however, even at the location of a chip, where the burr could be expected to engage the wood, there is no evidence of the burr tearing off.
The next step in the procedure is to perform a few edge-trailing strokes on the 6k stone. As an aside, the three images below show the effect of going directly to stropping on a single sheet of newspaper on the 6k stone.
Returning to the procedure (as described in the video) another blade was honed and a small burr was formed with edge-trailing strokes on the King 6k, the burr was folded by cutting into a piece of redwood. The blade was then given 3 edge-trailing strokes on the 6k stone to break-off and/or stand-up the burr.
The blade was then stropped on a single sheet of newspaper wrapped around the stone (6k side up). The residual burr is effectively removed by this step.
At this point, the blade easily passes Murray’s 3-finger test. The blade effortlessly draw-cuts paper and push cuts with some effort. Scrape-shaving arm hair can be achieved, but it does not catch hair above the skin. This is an excellent working edge for a knife but I have failed to produce a “shave-ready” straight razor by this technique. It appears that the greatest variable in this progression is the amount of metal removed during the post-wood-cutting step of edge-trailing strokes on the 6k stone. A few more strokes or greater pressure may have been beneficial.
Finally, the blade was stropped on a chromium oxide loaded horsehide strop, laying flat on the 6k stone.
It appears that the apex does not make contact with the strop on the right side and that the improvement is minimal. Perhaps a thicker, more compressible strip of leather would have a greater effect.
The above results should not be generalized to predict the capabilities of this sharpening technique. In particular, this blade was sharpened at a fixed angle, precluding the advantages of increasing the angle by freehand sharpening (making better contact with the apex). Also, low-angle straight razor blades will be deformed to a greater extent by the burr folding step than a 30 plus degree (inclusive) knife blade would be.