Hardness of coticule based on slurry color

I've read on this forum before that the slurry used on most coticules will darken after some number of passes.

I recently tried to remove scratches left by a 1k diamond plate by working the razor on the coticule with slurry in a circular fashion using reasonable pressure (way more than one would use when trying to get a sharp edge). For the first time, I noticed the slurry darken a bit after a 1/2 minute or so of circles. I have never seen the slurry change color when honing using normal, light pressure before.

Does this indicate that my coticule is on the harder end of the spectrum? It is currently the next stone I use to remove diamond plate scratches, but I am wondering if it is too hard for that purpose. Thanks for your thoughts.

Normally, darkening slurry indicates a Coti's speed. I test hardness with the fingernail test. Basically, you scratch the surface. No visable scratch = Hard Coti, Visable scratch = med Coti, Very distinct scratch = Soft coti. Also, Coticules that are pinker or darker are normally softer, Green, light yellow are normally hard. I've handled many, so I can tell by scratching the surface. You need to see several stones to understand. Basically, Coticules are hard, and run around 8k - 10k

Remember, the darkening of the slurry is due to metal removal. Try not to take more off than you need to to set the bevel properly.

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Originally Posted by Oak

I recently tried to remove scratches left by a 1k diamond plate

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To add to what zib and Croaker said, a 1k diamond plate is not recommended by DMT to lap waterstones. The abrasive embedded in the diamond plate isn't coarse enough to withstand the abrasive on the waterstone. It will begin to cut into the nickel plate that the diamonds are embedded in and ruin the plate.

Not sure what mfg made your diamond plate but DMT recommends the X, XX, or C for lapping and that under running water to wash away swarf. Also as soft as a coticule is, relative to other waterstones, I would hesitate to use one to remove scratches by rubbing it against another stone. Coticule is a valuable stone and I wouldn't want to wear it on anything but honing razors. Just my 2 bits.

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Originally Posted by JimmyHAD

To add to what zib and Croaker said, a 1k diamond plate is not recommended by DMT to lap waterstones. The abrasive embedded in the diamond plate isn't coarse enough to withstand the abrasive on the waterstone. It will begin to cut into the nickel plate that the diamonds are embedded in and ruin the plate.

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I think he meant the 1k scratches were on the razor, and was using the coticule to get rid of the scratch marks on the razor edge. :) But you are 100% correct! :D

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Originally Posted by avatar1999

I think he meant the 1k scratches were on the razor, and was using the coticule to get rid of the scratch marks on the razor edge. :) But you are 100% correct! :D

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:gaah: in retrospect I guess you're right. :)

Jimmy is right on it.
You have ruin your dmt already check in the middle of the dmt plate and you should see color changes. This is just learning process and i may be the first one done this to my plate.
if you want to test is your dmt problem try lap different stone if water color changes to black then it is dmt.
gl

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Originally Posted by JimmyHAD

:gaah: in retrospect I guess you're right. :)

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My fault for being unclear.

I used the DMT on the razor to set the bevel, but the scratches left behind seemed to prevent a smooth shave, even after a coti/slurry, BBW, coti/water progression. To remedy this, I went back to the coti with slurry. Still not much change. So, to make some progress, I experimented with using more pressure and circular strokes, and, voila, darkened slurry for the first time.

Sounds like this must be a pretty hard coticule. I may need a different stone to bridge the gap between a 1200 DMT and a BBW. I'd be curious to hear different opinions, though.

Thanks again

If I understand Bart's method correctly .... and I think I do .... I would set the bevel on the 1200 plate, hit the coticule with slurry to polish out some of the scratches and further correct said bevel. When I was satisfied with the results I would go to the bbw with slurry to improve the keenness and then the coticule with water only to finish.

I've done this more than once with good results. .... except since I don't care about scratches I didn't go to the coticule with slurry after the plate. :) I have, however, used the coticule with slurry to set a bevel and then went to the bbw as above. Time consuming to do it that way, and I don't ordinarily, but doable IME.

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Originally Posted by JimmyHAD

If I understand Bart's method correctly .... and I think I do .... I would set the bevel on the 1200 plate, hit the coticule with slurry to polish out some of the scratches and further correct said bevel. When I was satisfied with the results I would go to the bbw with slurry to improve the keenness and then the coticule with water only to finish.

I've done this more than once with good results. .... except since I don't care about scratches I didn't go to the coticule with slurry after the plate. :) I have, however, used the coticule with slurry to set a bevel and then went to the bbw as above. Time consuming to do it that way, and I don't ordinarily, but doable IME.

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Jimmy, I believe I've read him advocating dulling the razor (by using only the weight of the razor on the round part of a beer bottle or something) after coming off the 1200 plate to remove microchipping and then going back to the coticule.

If you can scratch a coticule with your fingernail that's one soft coticule. There aren't too many minerals you can do that to, talc, gypsum, maybe calcite.

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Originally Posted by Oak

My fault for being unclear.

I used the DMT on the razor to set the bevel, but the scratches left behind seemed to prevent a smooth shave, even after a coti/slurry, BBW, coti/water progression. To remedy this, I went back to the coti with slurry. Still not much change. So, to make some progress, I experimented with using more pressure and circular strokes, and, voila, darkened slurry for the first time.

Sounds like this must be a pretty hard coticule. I may need a different stone to bridge the gap between a 1200 DMT and a BBW. I'd be curious to hear different opinions, though.

Thanks again

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When you went to coticule with slurry, how many circular strokes did you do total before you checked the bevel? Sometimes it can take quite a while. Yes, the coti with slurry cuts relatively fast, but it's not SUPER fast (in most cases.)

Also, the slurry doesn't have to be really thick. Just the consistency of milk. If it's like a paste, then you have it way too thick.

I don't own a 1200 DMT, but I think you should be able to go to a coticule after that. I go from a Norton 1k to Coti and have had no problems. You may have to do more passes than you have already, but I'm sure it will come around eventually :)

I actually haven't had a chance to finish it out yet. I didn't keep track of the time, but it wasn't long at all. I checked the edge through a 100x scope periodically. Now that the deep DMT scratches are worn away, I'll switch to regular light passes with slurry.

Thanks

I'm confused enough about how the OP worked through the grit/polishing progression that I'd hate to be tested on it, but isn't a good part of working 'up the ladder' the intention to spare using the coticule as much as possible?

I don't find the coticule inadequate (with slurry) as a cutter, even if you're sharpening something that's 'dull as a butterknife'. As long as it doesn't have a bad nick, the coticule will sharpen it, and promptly enough too. It does, however, wear away rock as well as metal.

I can't use a coticule without flinching if there's an alternative stone feasible. I often polish on a BBW with water, before going to the coticule with a light slurry. I don't have a fixed progression and sometimes use other stones pre-coticule, but all are pushed to the limit of fineness until the coticule is NECESSARY to improve the edge further.

I'm not sure I've learned much about coticules that way but it's helped improve my skills with BBW's and japanese stones.

I suppose I could spare the coticule more, but a) this one seems very hard and will not likely be even dented in my lifetime and b) I just like using it. If I can use the same stone for coarser work with slurry and finishing work with water, then all the better.

But, to each his own. I certainly understand where you are coming from. I would probably be singing a different tune with a soft coticule.