Originally Posted by
Bart
I think we have to bear in mind that 50 years and longer ago, there were no Nortons, no DMT's, no Shaptons. The bulk of synthetic hones people had access to were much too coarse to be used on razors. Coticules were used as work horses. Loom strops, such as the model that Dovo sells till this day forward, were commonly used with a red paste, to refine the edge further after it came off the coticule. This traditional method of honing is still taught today on various straight razor revival courses in Belgium (and I guess also in other countries).
This use of the coticule is completely different than the on SRP mostly endorsed use of it as a finishing hone, after sharpening on hones that didn't exsist in the "vintage" days.
For the traditional use as a sharpening hone that fits in the realm of the Norton 4K and even of the DMT1200, it is imperative that the coticule in question has good slurry formation abilities. But even that doesn't tell everything. I have used coticules that raised slurry very easily, but still couldn't move hard razor's steel fast enough to be used for serious sharpening of a blunt edge. Those exact same coticules worked just fine on the softer steel of kitchen knifes. The rate at which the slurry darkens while honing is good indication for assessing the rate at which it removes steel.
On the other end of honing, for polishing an already keen edge, the coticule does not need to move steel fast. Slurry is to be avoided so the very softest stones are to be ruled out. After that, we're left with the question how much difference there is between the medium and hard stones and also if the hardness by itself tells the whole story. I don't know.
I have visited different former mining sites, climbed a few fences and took calculated health risks to pick up rocks of raw coticule. Having them cut to strips costed me more than purchasing a few hones at Ardennes (which I have also done, cheers Rob:)). It took me and my pal Kris countless hours to lap a few of the most promising samples completely flat. Among them are a few glass-hard specimen. At first, I thought they were not doing anything. Although under 40X magnification the steel shows a beautiful polished surface, the edges were always unsatisfactory.
It was not before I bought an outstanding high-grit synthetic hone (the Naniwa Chosera 10K), that I discovered the virtues of those hard coticules. They turn a fantastic edge into a freekingly fantastic edge. But, to reiterate, if you 'd expect those particular samples to improove the given keenness of an edge, then you're going to be dissapointed.
Many coticules offer a good comprise between being avid cutters with slurry and smooth polishers with water. In most cases, I am strongly convinced that the final results are much more limited by the honers skills and not so much by the hones capabilities. In the extremes, some coticules might polish a bit finer and others might cut more rapidly, but it's still the call of the honer how to use it and where to place it in a progression.
Rob, I would very much like to assess coticules for you. It would allow me to gather more empirical data about these historical hones to which I have develloped such a big fondness, and it could help you to finetune your differentiaton system.
Best regards,
Bart.