What abrasive to remove discoloration from M4 satin finish blade?

C

Cementite

Joined
Oct 10, 2023
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Hey, all, I have a PM2 in M4 with the satin finish (kind of looks brushed, with scratches perpendicular to the blade) that I bought new last fall, and I've tried to keep oil/grease on the blade, but somehow I got a tiny pinhead-sized bit of discoloration on the blade, I don't know how, maybe sweat? It's not pitted that I can see with a loupe -- just slightly discolored.

Anyway, I would like to buff it off with something, maybe with a dremel cloth wheel with some jeweller's rouge? I want to remove the discoloration, but I also don't want to mar the finish by putting a big polished area in the middle of the satin-finished blade.

Can anyone advise me on how to do this? I'm fairly handy and have a variety of tools and materials (a large variety of sandpaper grits; 3000 and 8000 grit diamond pastes; white, green, gold and black jeweller's rouges; strops, buffing wheels, etc.)...I'm just not sure where to start, and am also unclear on whether I'm better off erring on the side of "too coarse" or "too fine" for my first attempt...

Maybe the question I should be asking is, what abrasive and grit size does Spyderco use for its final finish on the satin-finished M4 blades?

Thanks in advance for any advice.
 
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It is a High Carbon blade and it will do that.
Trying to maintain the appearance you want is a lost cause.

Trade it for something more stainless
 
Sadly, that's life with M4. You can't really remove a spot with it being obvious so if you try, you'll need to refinish the entire blade. Stains will still appear and you'll be doing this over and over. Sorry for the bad news.
 
Try Flitz it works great for stopping patina and protect from pitting and tarnishing. Not the best for removing scratches but can and will bring back a brilliant natural shine
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Well you just aren't going to be able to clean it in one spot and duplicate the finish on the rest of the blade, even if you used exactly what they use in the factory the scratch pattern would end up different. You could try to remove the spot with a brass brush and some polishing compound, then go over the whole blade with 1000 grit paper. But it's a lost cause to try to keep M4 looking perfect on a knife you actually use, the carbon content is just too high.
 
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Patina is wonderful, and protective. In your position, I'd be trying to get it to cover the whole blade. Users of carbon steel kitchen knives do this routinely, mostly by slicing juicy meat, but sometimes forcing with coffee or other things.
 
fishface5 said:
then go over the whole blade with 1000 grit paper
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Is that the correct grit for that type brushed finish? I've fit new scales to blades and in the process of working along the edges of the tang I've used 400-600 grit and gotten much finer scratches than on most brushed finish blades. I was wondering if 200 or 320 wet/dry paper would be more appropriate. Of course the OP could do experiments on a random tool or piece of steel to see how the paper works.
To the OP I would suggest starting with some weak rubbing compound or even toothpaste, go lightly and see if you can reduce the spot. A lot of people have have carbon steel blades that have turned fairly dark, some people even force it on their own. I have an old blade I bought that is medium darkness and hasn't changed. I have a total of 7 blades in M4, Rex45 and K390 that are a number of years old, are carried and used regularly, and are still clean and shiny. It depends on your climate, how you use the blade, and how clean you keep it.
 
Ajack60 said:
Go look up “Super Eraser” and get one. You can thank me later.
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that will change the finish in the area used . I stopped using them for that reason....other than on really rusty stuff that didn't matter about the finish. op isnt gonna want those markings and scratches from using one.......
 
Thanks for the replies, everyone. I appreciate your help.

1000 grit? That sounds high to me, though I really have no idea. I would've guessed something like 600 or even 220. I tried steel wool, which didn't touch it, so I'm sure a brass brush would do nothing...M4 = HARD.

Really hoping Sal or Eric might weigh in with how they finished it in CO...
 
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