A question about "Patina".

[oldmanrunning]

I have never really got this thing about patina, unless it is the uniform dull look that comes to metal with use and age and i generally wipe and sometimes wash my blades after use. Anyhow i let some of my knives develop a patina, but have decided enough is enough i polished the blades on a #57 Half Whittler and a Yeller cv peanut, as i had expected the GEC came up like new but the peanut has some marks as if chrome has lifted although there is no discernable feel to the marks.
I have a Case Texas Jack that also has a patina but i dont want to polish it for fear of what may be under it.
I took some photos that may help, despite my sketchy camera work, i should be interested if anyone has thoughts on this.
Thank in advance OMR...

 

[Ryouchijtx]

Mm in my experience your fingers may not be able to discern a difference while rubbing across but it is there is one in photo alone.
The only way to get rid of this underlying patina would be to regrind the blade or buff it completely over with a wheel unless you've already done so.
With hand work/elbow grease you can't get rid of serious pepper spotting or darker spots of patina all the time and need machinery as I've come across.

 

[jc57]

That looks more like it was etched rather than just patinated. I have never had a problem removing a simple food-created patina from polished Case CV blades with just some Simichrome metal polish paste and a paper towel, and optionally some Renaissance Wax for the final shine.

Unless that is a very old Case knife there shouldn't be a chrome plating on the blades, though I believe they did chrome some of their larger hunting knives many decades ago.

 

[Obsessed with Edges]

Just polish it. Case's CV does 'spot' easily on the surface, with oxide; sometimes it'll be red rust, and other times just black oxide, which is harmless. There's no 'chrome' on the surface that can lift, per se. The chrome that's in CV ('chrome vanadium') steel is miniscule as a percentage of the blade's makeup (less than 1%, as is also the vanadium content), and is homogenously distributed throughout the steel. Polishing with Flitz, Simichrome or similar polishing pastes will clean up those spots pretty easily. They don't look pitted yet, so it shouldn't be hard to fix.


David

 

[oldmanrunning]

Blimey that was quick Tim, i have only just done the polishing, so am i to assume that i can buff off the rest of the shiny coating to leave an unpolished finish ? I recently had a Laguiole made for me with a plain carbon steel blade and i much prefer it to the highly polished 12C27 steel that most of my other French knives have.
OMR.

 

[oldmanrunning]

Thanks John and David, according to the dots i believe it was made in 2014 and i polished it with Autosol a chrome polish and that is as good as it got but i did not spend to much time on it to be honest.

OMR.

 

[afishhunter]

Chrome does not develop a patina. Remember back when cars had chrome metal bumpers and not the painted plastic "bumpers" of today?

I'm not sure why the peanut did not clean up evenly. If regular metal polisd does not work, maybe some pilishing compound on a cotton Dremel polishing wheel would work?

 

[Obsessed with Edges]

Blimey that was quick Tim, i have only just done the polishing, so am i to assume that i can buff off the rest of the shiny coating to leave an unpolished finish ? I recently had a Laguiole made for me with a plain carbon steel blade and i much prefer it to the highly polished 12C27 steel that most of my other French knives have.
OMR.

The 'shiny coating' on CV steel is just the steel itself, polished (Case tumbles the blades in abrasive media to accomplish this). Buffing the blade will likely polish it a bit more, or a lot more if the buffing is done with some polishing compound. It won't remove the shine, unless the buffing wheel is extremely dirty/gritty. As previously surmised, the dullish areas on the steel almost look etched, as with some sort of chemical exposure. Some heavier polishing or even sanding with high-grit sandpaper (800-2000+) will start to bring up the shine again, if the steel is etched. If you DON'T want the shine, sand the blade with some 600-grit or lower-grit sandpaper, maybe down to 320 or so, to leave a 'satin' or 'brushed' finish.


David

 

[jc57]

You been using that nut to open bottles of muriatic acid or something? That looks for all the world like a shiny surface plating of chrome has been removed down to some underlying metal, but Case's blades are not plated - just homogenous carbon Alloy steel throughout. Unless the blade metal itself had a flaw of some kind, or if Autosol (which I am not familiar with) is not safe for use on bare steel.

 

[Obsessed with Edges]

Thanks John and David, according to the dots i believe it was made in 2014 and i polished it with Autosol a chrome polish and that is as good as it got but i did not spend to much time on it to be honest.

OMR.

If the dull areas are actually etched (by chemicals or whatever), it may take some more work to restore the finish, as per my suggestions in post #8. Etching goes deeper into the steel, leaving a micro-pitted surface which gives it that dull grey appearance; if so, the polishing compound alone may not be aggressive enough to completely fix it.


David

 

[Will Power]

I tend to agree with you about 'patina' (nascent rust....) It is interesting though how different carbon steels behave: Böker's carbon seems to take on a very uniform colour, CASE too generally and GEC appears to retain more of its original shine than others. Maybe their polishing process is more rigorous? Another factor in all this can simply be oils from the tang or fingers giving a different degree of patination, so when it comes to cleaning or polishing, a more uneven appearance may result. I often carefully clean up my carbon blades with a Scotchbrite or similar, from time to time. It not only gives a nice clean matte appearance, but seems to encourage a more even patina in the future. Until you clean it off again.....

French Laguioles often have mirror polishing in stainless which is a fingerprint hell, some makers such as Fontenille-Pataud offer matte brushed finishes for blade, backspring and bolster as an alternative.

Thanks, Will