Thread: Black lines/marks in a coticule?

So I recently obtained a small old vintage coticule for pretty cheap. The thing is it has quite a few thin black lines as well as blotchy black lines through it. I assume these are impurities? The stone doesn't appear to be glued, by the way, as there is a very natural looking line (uneven with bits of the darker material imbedded in the yellow coti at the division) dividing the one side from the other.

Anyways, to test it I took an old dull knife I had lying around to it just to test it out (because I wouldn't dare take my razor to it if it might destroy the edge). Worked up a little slurry just honing (no slurry stone after all) then watered it down before it got too thick. Repeated that once more then did a set of strokes with clear water. Just about 10 minutes effort and that knife had an edge like it hasn't seen in a long time!

So, my question is, is this hone serviceable for razors? Will the lines/impurities (?) effect the honing of a razor? It certainly works for knives, and I can put it to plenty of use for that, so its no loss there if it doesn't work for razors. I've also learned that I really like these things so far. Being able to change the cutting properties of the stone with a little slurry or a little water is great. Also they feel very nice to use too! Anyways, thanks for any input!

Congratulations on finding an old coticule natural, you should post pics of it! We love looking at pics of hones people find.

I have a few coticules with those black lines, often called veins. They are impurities in the coticule, but are cosmetic and don't really affect honing. A "select" grade coticule would be free of such cosmetic flaws, but they could be found on "standard" grade. Both grades hone the same, they are just graded for cosmetics. I myself often like the lines, and think they give coticules even more character and personality than they already have.

For a time, I used to believe that such lines indicated a "soft" coticule, because the two of mine that have them are very aggressive cutters (like the one pictured below). But then I picked up one of my very hardest coticules, and it had them as well. So I rethought that. I don't have any with blotches, but I'd love to find one, I admire the pictures of those I see with interesting botches.

Below is a picture of a 5 x 3 x .8" natural combo I have with similar lines or veins, almost like a spider web on the surface:

IIRC the lines are inclusions of magnesium oxide?

I agree, they give each stone that has them character. No two are identical.

The first picture is one of my coticules. The second one is not, but it's one of the nicest ones I've ever seen.





Chris L

It's interesting, I read a thread from Coticule.be about this topic this morning. This post by Bart was particularly enlightening

Originally Posted by Bart

Black lines and dots in a Coticule are almost always deposits of Manganese dioxide (Mn0²)also known as Pyrolusite.
The crystals have a hardness of 2-5 on the Mohs scale. That's too low to have much effect on hardened steel. Besides that, the crystals cleave very easily (Pyrolusite is extremely brittle), and quickly crumble to a fineness way below any significance for honing.

Manganese plays a key role in the formation of spessartine garnet crystals, which is the abrasive medium in Coticules. In abundant presence of manganese during the formation, some 480 million years ago, these black ores of Manganese leftover signify that a particular Coticule is densely packed with fine garnets. These stones nearly invariably turn out to be fast and fine cutters. In that sense a few traces of black are a sign of excellent quality, rather than to be considered a flaw.

Here is a pic of mine:

I find the variations very attractive. This vintage glued coti has some cool stuff in it that doesn't have any negative effect I can discern. Might even be helpful.

Jimmy, that is one SLAB of coticule! Wow is that thing thick. I love the blotches too. No way you'd lose that one in a stack of coticules, totally unique.

Chris, I love the deep golden color and symmetric lines on yours. Almost looks Japanese or something.

Originally Posted by FatboySlim

Jimmy, that is one SLAB of coticule! Wow is that thing thick. I love the blotches too. No way you'd lose that one in a stack of coticules, totally unique.

Chris, I love the deep golden color and symmetric lines on yours. Almost looks Japanese or something.

Thanks. The color of the photo is a bit off, I'm afraid. The background is actually white.


Chris L

Well this is all very good news! And very nice pictures! If lines and blots give a coticule character this one has quite a bit!

Heres a few pictures for you guys:





And heres:



This just makes me love the little thing more already. I think its about time to take a razor to it as well! By the way, what would the dark backing material be? I know its slate if its glued and BBW if its a combo, but I don't know quite enough to tell here. Thanks for your input again guys!

The uneven line gives away the fact that you have a natural combo coticule mated naturally with BBW.

Great looking stone you have there.

Chris L

It is?!?! Nice! I tried the knife on BBW side and didn't notice much of a draw compared to the coti side, so I figured it must not be BBW. I guess thats why you have to use a slurry with the BBW? (at least I think I remember reading that you do...) This is excellent news though! Thank you for pointing that out!