DMT Diasharp got little rust spots after honing with water over 5 minute period

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obsessis

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Jul 2, 2009
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I decided to try honing a Cold Steel Kukri that comes with a primary bevel but unsharpened on my DMT8XC. I put some water on it and honed for about five to ten minutes before I washed it off. When I was done, there were rust spots on the hone where there were none before - this was the second time I had used it.

Is this normal? Is there anyway to get it off? I'm now concerned that the spots will get bigger and ruin the stone or that I won't be able to use water on it again.

Anyone who uses water frequently have any comments or suggestions?
 
Don't worry too much, about the rust spots. They can be dealt with. For the time being, the rust spots can be halted (without growing) by cleaning the hone. You can use dish soap and HOT water to clean the hone, then rinse in HOT water. The hot water will ensure that the moisture evaporates rapidly when drying. You can also wipe down the hone with isopropyl alcohol afterwards. That'll dry up any residual moisture.

For removing the rust spots, a product called Bar Keepers Friend works very well. It can usually be found in the grocery store or other supermarkets, in the section where you'd find other kitchen/household cleansers. It's unique, in that it uses oxalic acid as the active ingredient. Oxalic acid basically eats rust. When used as recommended, it is very effective. It's a powder (such as Comet), and when made into a paste, by mixing with a little water, it can be applied very locally to the rust spots. Leave it on the spot for maybe 15-30 seconds, maybe scrub a little bit with a toothbrush, then rinse thoroughly with water. The rust spots will ordinarily disappear almost instantly. Make sure to rinse VERY thoroughly. The oxalic acid is very effective at removing rust, but will also corrode the metal of the hone if left in place too long. Bar Keepers Friend is a very effective cleaner, but make sure to use it as directed, according to the instructions on the container.
 
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Another possibility, in the future, is to use the hone dry, or with an alternative liquid. Many here have used the DMT hones with some dish soap, which serves essentially the same purpose. Add a little water to that, even. Does an effective job of suspending the metal particles, and makes the clean-up afterwards that much easier.

I ordinarily use my DMT hones dry. They can be occasionally rinsed off, or wiped down with a damp paper towel. That will minimize the hone's exposure to moisture. Clean afterwards, as I recommended earlier, with HOT water and dish soap.

The metal coating of the hone is nickel, embedded with diamond particles. The rust spots are likely due to the steel removed from the blade, which rusts, and not the hone itself. So, if some care is taken to thoroughly clean the metal swarf from the hone, the rust issue should be minimized.
 
Thanks for the tips about HOT water, BKF (I use it on my Spyderco Hones already) and Dish Soap.

The thing is, I couldn't believe that it would rust after 5 minutes of exposure......I'd think it'd need to be much longer or wrapped up wet. The rust spots appeared within 5 minutes when I washed everything off....could it be due to the metal type? It was a carbon steel from Cold Steel, their cheap stuff for their cheap kukri's and machete's.

I love the DMT products and this was the first time using oil - I was using coticules, an Escher and a Japanese whetstone to hone some knives so I thought I'd give it a try even though I didn't need to.
 
carbon steels rust really quickly. It literally happens when you're looking at it, that's what you're seeing in 5 minutes. There's some brown patches on my dmt's here and there, but it's easily washed off, taken care of, which leads me to believe it's not the dmt's nickel platings that are reacting with H2O / O2
 
obsessis said:
Thanks for the tips about HOT water, BKF (I use it on my Spyderco Hones already) and Dish Soap.

The thing is, I couldn't believe that it would rust after 5 minutes of exposure......I'd think it'd need to be much longer or wrapped up wet. The rust spots appeared within 5 minutes when I washed everything off....could it be due to the metal type? It was a carbon steel from Cold Steel, their cheap stuff for their cheap kukri's and machete's.

I love the DMT products and this was the first time using oil - I was using coticules, an Escher and a Japanese whetstone to hone some knives so I thought I'd give it a try even though I didn't need to.
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As Zyhano pointed out, carbon steel will rust very quickly. And if you think about it, when in the form of carbon steel dust, each particle has ALL of it's surface area exposed to the moisture. The reaction will happen even faster. Many have learned that polishing a carbon steel blade will minimize rust issues, because polishing will refine and close up some of the pores in the surface of the steel (reducing the exposed surface area, in effect, and also minimizing opportunity for moisture to be trapped in the pores). There are even variations among specific types of carbon steel. Some will rust to red color immediately, other's will more readily form a black oxide instead.

An interesting test would be to use the hone dry for a bit, and wipe some of the dry swarf from the hone or blade with a paper towel, and put some water on the swarf on the towel. Watch it, and see if/how fast it rusts. That might be an eye-opener. I'm tempted to try that myself.

So, bottom line, do as much as you can to thoroughly scrub the hone clean after each use. I think DMT recommends using some powdered cleanser (like Comet or Ajax) with water, the goal being to scrub away as much of the steel swarf from the hone as possible. As I mentioned earlier, the Bar Keepers Friend takes it one step further, with the chemical action of the oxalic acid. That'll dissolve steel particles that can't otherwise be reached by scrubbing/rinsing. The BKF is perfect for cleaning ceramic hones in this manner, also.
 
As others have said, steel shavings have huge surface area to volume ratios and rust quickly. The rust is not the DMTs but the steel you put on it during sharpening. I have done this to mine many times...it goes away on its own with use (or you can scrub it away with various cleaners).
 
Use water with baking soda in it. Will cause the steel to be much less prone to rusting and still be easy to clean up.
 
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