Thread: Combo coticule conundrum

Here is what looks like a natural combo stone I grabbed from a local antique shop for $15. Great, right? There is only one problem, and it's a big one.

It has been used nearly to death, has a significant dish in the center/side of it and...To get the thing lapped flat, it will end up at max thickness of 0.350". How fragile are these stones?

I would like to really lap the whole thing flat, but I may just make 2 triangular stones out of this one for traveling. I really dig the iridescent spotted purple side, it looks pretty cool under sunlight.

You should ask Howard about this really. My understanding is coticules are very fragile, that's why they bond them to slate for the stability. Also to flatten out a natural stone to that degree will take some doing. Its not fast like a Norton.

so the yellow is dished out, eh? looks like you'll either have to be happy with the smaller sizes, but i personally will keep it large. there's plenty of stone left for honing many many razors - these don't seem to wear much at all.
the blues are rather sturdy (no I won't tell you how i know) and the yellow isn't all that delicate - it's a stone afterall. if you drop it it'll break, but under normal usage I won't expect any problems.
you may want to make a box for storage, though.

and yes check with howard.

Originally Posted by gugi

so the yellow is dished out, eh? looks like you'll either have to be happy with the smaller sizes, but i personally will keep it large. there's plenty of stone left for honing many many razors - these don't seem to wear much at all.
the blues are rather sturdy (no I won't tell you how i know) and the yellow isn't all that delicate - it's a stone afterall. if you drop it it'll break, but under normal usage I won't expect any problems.
you may want to make a box for storage, though.

and yes check with howard.

Yeah, pretty bad, pic #2 shows it, the dark part (excluding the water coloration) is the dished spot. Worse than it looked at the local antique shop.
BUT...what can you do when the HAD bug takes hold of you?

That is a conundrum. What a beautiful stone though. If it were my stone, I would succumb to temptation and lap both sides. If I didn't pay a lot for it and it broke, I'd use a bout from it, or cut it up/have it cut up into combo slurry stones, keep a few for myself and sell the rest off inexpensively to others.

Chris L

If it were my stone I would opt to lap the yellow side and use it. There still looks to be plenty of life left in that stone.

Originally Posted by thebigspendur

You should ask Howard about this really. My understanding is coticules are very fragile, that's why they bond them to slate for the stability. Also to flatten out a natural stone to that degree will take some doing. Its not fast like a Norton.

That's what I have read too. Meh, for the price I would be fine with 2 stones. I started lapping it and I would say it's harder than the Norton but not as hard as my Carborundum hones...and not as hard as my Spyderco hones (heh heh heh).

Right now, I would rather have access to both sides of a smaller stone than resort to cementing the thing to something to stabilize it and only using the yellow side. I am going to set it aside and think about it for a while.

You ARE lucky! Nice find and great price. You're fortunate in that it looks like they used the blue side more than the yellow side. The dishing in the center of the coticule is a problem and you'll just have to figure out whether you want two really flat stones or one flat, but thinner stone. In truth, if it ends up being really flat at .35", that's not bad at all. Coticule never gets really thick as it is found as veins in the blue rock. It cooled quickly and that's why the crystals are so small and it's a finer grit. I flatten coticules on a DMT 325 grit Coarse continuous diamond stone under running water in the kitchen sink. It's always sad to see coticule washing down the drain so flatten only as much as you have to. Your photo of the lighter areas surrounding the dish illustrate what I tell folks when they're flattening stones. Just look at the lighter area and keep flattening until it's uniformly light. This goes for new coticules fresh from the quarry too as well as Nortons and other stones.

I checked the thinnest point with the blades of my calipers, and then subtracted .025" just to be conservative, to get my max thickness after total lapping.

The overall dimensions of the stone are 5.39" x 2.2". Not too bad huh?

I am definitely going to mount it to glass, I will look around and see what kind of waterproof adhesive I could use.

I have been lapping with the DMT coarse, but it's slow going. Since I am currently using Spyderco hones, and am happy with the results I get from them, this is going to be a hobby stone anyhow.

If you guys have any other ideas, just chime in! I appreciate any suggestions, big or small.

Update: I lapped it flat on the yellow side and took it for a test hone (water only, I have enough rough stones).

Not bad, but not as fine a finish as the Spyderco UF. It does give a lot more feedback, but I'm not sure I like that.

With the UF; I can really feel when the edge is ready to test shave, almost like the hone feels...softer?

and the razor slides lightly over the hone so I can use a superlight touch.


I dunno, I will have to play with this coticule for a while before I make any decisions. It's so neat, I really want to use it