CV blade and patina on Case knives

T

TN Jack

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Nov 10, 2018
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I have read about patina on knife blades, particularly on CV blades on Case knives. What is patina, and is it harmful for the blade? Or is it just harmless discoloring?

I have always leaned towards stainless steel bladed knives, but I am considering taking the plunge and getting a Case trapper with CV steel just for something different.
 
Patina is a different type of oxidation. While it doesn't rust-proof a knife, it does make it more resistant to the typical red rust we'd think of as oxidation. It gives a blade character, and changes with use and time. Not everyone likes it, and some really enjoy it. If you are perfectionist, it might not be for you, but if you don't mind viewing the blade as a changing and evolving thing, then you may get a lot of enjoyment out of it.
 
TN Jack said:
I have read about patina on knife blades, particularly on CV blades on Case knives. What is patina, and is it harmful for the blade? Or is it just harmless discoloring?

I have always leaned towards stainless steel bladed knives, but I am considering taking the plunge and getting a Case trapper with CV steel just for something different.
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Patina is a form of rust. But it is black oxide instead of red oxide. The conditions under which black oxide forms are different than those under which red oxide forms. Black oxide tends not to cause pitting and is mostly surface corrosion. Pitting corrosion greatly weakens the steel, surface corrosion much less so. So, patina isn't significantly harmful for a blade, but it is more than "harmless discoloring".

If you put a "patinaed" blade and a fresh blade unprotected out in the rain and weather, they will corrode and form red rust at reasonably the same rate.
 
knarfeng said:
Patina is a form of rust. But it is black oxide instead of red oxide. The conditions under which black oxide forms are different than those under which red oxide forms. Black oxide tends not to cause pitting and is mostly surface corrosion. Pitting corrosion greatly weakens the steel, surface corrosion much less so. So, patina isn't significantly harmful for a blade, but it is more than "harmless discoloring".

If you put a "patinaed" blade and a fresh blade unprotected out in the rain and weather, they will corrode and form red rust at reasonably the same rate.
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Very good, simple answer.
Spot on.
 
Patina occurs when the carbon in the steel reacts with acidic materials -- fruits, veggies, meat, etc. Not harmful and does not impart any taste to food that I can detect, anyway. Had a gorgeous old French chef's knife that was practically black after a couple of decades of use. My favorite hunting knives carry patinas that are memories of great hunts.
 
My Christmas knife is a Dark Red Jigged Bone Trapper in CV. I bought it just to carry during December / Christmas ; it is in my pocket now. Generally I force the patina and play around to see what happens. This time I had decided to keep the blade polished and silver color.

Turns out I just let the patina form naturally. Three days of cutting just a few oranges and apples and pears and it has a rainbow on it of colors. It looks like a layer of goldish brown with a nice mirror blue over that with the gold peaking out around the edges. To my eye it looks very nice and it would be a shame to polish it off. It happened so fast I could watch this form as I washed the knife off under very hot water at the kitchen faucet.

Now the question is do I polish it off before next Christmas or keep it on to remind me of this Christmas next Christmas. We'll see. I put some knife "rust erasers" in the cart on line but have not bought them yet. I thought Bar Keeper's Friend was what I wanted for this but apparently there are better ways to go.

Any suggestions for removing patina ?

Being a person who grew up always having stainless steel knives in the kitchen I find those that patina fascinating (and I like using them better as well).

I recommend just using the knife to cut food and not force the patina and just watch it form and change over time. You can always experiment with forcing a patina later; even making patterns on the blade.

Last night I was putting various brands of mustard on my knife that has HAP40 steel.
That alloy may not be "stainless" but it was laughing at my efforts. I was even leaving it in a very slightly warm toaster oven to accelerate the reaction. I now have just the lightest tan color on the blade . . . but that's another thread . . .
 
Alberta Ed said:
Patina occurs when the carbon in the steel reacts with acidic materials -- fruits, veggies, meat, etc. Not harmful and does not impart any taste to food that I can detect, anyway. Had a gorgeous old French chef's knife that was practically black after a couple of decades of use. My favorite hunting knives carry patinas that are memories of great hunts.
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You mean the iron. The carbon does not react.
 
Purely anecdotal, but I find that when I cut fruit with a carbon steel blade, the metallic taste it imparts to the food goes away once an even patina is formed.
 
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