Thread: Assess coticule quality?

Originally Posted by kingreverent

Hi all and especially to Bart.
I read often that a str8 razor is getting sharp when it start to "undercut" the slurry instead of pushing the slurry forth with the bevel.
Is this real a sign of sharpness, or is it only some kind of urban legend?
My coticule never undercuts the slurry, but I do get excellent bevels.

Best regards

As a matter of fact, I always pay a lot of attention to what the fluid on the hone does during the passage of the razor. In my opinion, that's all part of what is often called "feedback" of a particular hone: all things that can be felt, heard or seen while honing.

Whether water or slurry runs up the razor, depends on a few variables, and I wouldn't consider water or slurry running up the razor a sign of keenness, but it does tell me certain things about my stroke. For instance: if you hone a smiling edge, and you don't do anything specific to improve contact with the heel and toe of the razor, the result will be a razor with a sharp middle part and a dull toe and heel. For tackling that problem the "rolling X-stroke" allows for better contact with the hone along the entire edge. But how much "rolling" does one needs to apply to his stroke? The answer is: watch the water (or slurry) run up the blade. Set your mind at making the water run up the heel section first, then up the middle section, and finally at the end of the stroke, up the toe. Focus on that, watch the water (slurry) and your arm will make it happen almost automatically.

The same thing works equally with slightly warped razors. Watch the fluid and it 'll tell you where and how to fumble with your stroke to maintain contact with all parts of such a blade.

As for sharpness: if you take a blade with a serious roundness to its bevel, such as many old razors coming from Ebay or an edge stropped to oblivion by ignorant hands, that blade will tend to push a wave of fluid in front of the edge without it running up the bevel. That effect is most apparent when the layer of fluid is thin and the blade is still dry. As soon as the blade becomes wet, the water will run up more easily, due to cohesive forces in the water molecules. But if you observe real close how the water searches the easiest way to run up the bevel you 'll now where that bevel is starting to develop and which part is staying behind. I'm not saying that I'm relying on that alone, while honing, but it does often tell me when not to bother with a TPT just yet, but keep on going a bit further.

On a coticule with slurry, I have witnessed many times how the slurry runs up the bevel very well during the first few laps and then starts to be more pushed in front. That's because the use of slurry on a coticule has some abrasive effect on the bevel tip of the edge. The garnets are removing metal from the sides of the bevel quickly, but they also meet with the tip. That's why you always should finish on a coticule with water only. That way the garnets stay embedded in the surface and while the coticule cut much slower in that fashion, the abrasive effect on the bevel tip is prohibited. I generally hone during my finishing stage on the coticule with water till I see a clear improvement of the water running up the bevel again. Then I perform a final TPT, and if everything checks out, I move to the strop and test shave.

As to razors "undercutting" the slurry, I think it depends a bit on your definiton of that verb. Sure, an edge will always push a fluid forth, but an amount of it will run up that bevel, and there is some relation between the width of the tip and the amount of fluid running up. Learning how to read that, takes experience, and I believe you could easily do without that skill, if you chose to. Some people have stated they can feel it in the way a razor rides the hone, when it is sharp. I personally am not blessed with such "fingerspitzengefuhl", as the Germans say, but what works for someone might not work for another, and vice versa.

I hope this answers your question,

Regards,

Bart.