When Does Patina Become Rust?

[Scandi Grind]

Hey all,

My question is pretty much in the title. I have a high carbon blade that I noticed developed a spot that I thought might be rust. After cleaning it off, and before I could convince myself not to, I decided to give a forced mustard patina a try (something I have never done before.) I was hoping to reduce maintenance a bit and see if it had nice looking results, but I ended up with a few lines and spots on the blade that are more orange and I'm not sure if I should scrub that out.

When does patina become corrosion that has to be removed?

[Eli Chaps]

In general...

Red/orange = bad

Black/gray = okay

[JSumm]

What steel is it?

[Scandi Grind]

It is a Mora robust actually, and I don't know what steel they use for it. I decided this was a good cheap knife to try a patina on before trying it on anything more expensive.

[JSumm]

Ok, yeah I think they list theirs as carbon steel and that is it. Probably based on the price that is fine. I have had "stainless steels" (ZDP-189 I'm looking at you) rust but not patina. Then there is K390 that seems to patina relatively easy, but not rust as easy. Even compared to M4. Just got my first sample of Cruwear. Letting it sit in some beef blood for 20 minutes hasn't shown any signs of patina yet, where as K390 would have some blue or amber sheen by now. I would keep an eye out for bright orange spots or lines. Typically if you catch it fast you can rub it off or scratch it off. Hard to really know unless you push it. If you are concerned about it, you could always rub it down with vasoline.

[Eli Chaps]

Make a paste out of a little Bar Keeper's Friend powder and water or baking soda and lemon juice if you can't find it and rub on the orange spots. Give it 30secs or so and then scrub with a sponge. See if that gets it.

I wouldn't use Vasoline on my knives.

[Scandi Grind]

Thanks for the advice.

I first heard about Bar Keeper's Friend on this forum, but I've never come across it before. Where is that stuff available? I suppose you can probably get it on Amazon.

[Eli Chaps]

It's in a lot of grocery stores. Don't get the cream, it sucks. Stick with the powder.

And yes, it is on Amazon. Great stuff to have around, especially if you use stainless cookware. :)

[yablanowitz]

Thanks for the advice.

I first heard about Bar Keeper's Friend on this forum, but I've never come across it before. Where is that stuff available? I suppose you can probably get it on Amazon.

I buy mine at my local Ace Hardware store.

[JSumm]

Make a paste out of a little Bar Keeper's Friend powder and water or baking soda and lemon juice if you can't find it and rub on the orange spots. Give it 30secs or so and then scrub with a sponge. See if that gets it.

I wouldn't use Vasoline on my knives.

Just curious, why not? I don't coat any of my blades. But when I did I used Vasoline. Mineral oil that actually sticks to the blade. Basically food safe and its cheap and readily available. Worked great, but I like a patina, so I stopped using it.

[Eli Chaps]

Make a paste out of a little Bar Keeper's Friend powder and water or baking soda and lemon juice if you can't find it and rub on the orange spots. Give it 30secs or so and then scrub with a sponge. See if that gets it.

I wouldn't use Vasoline on my knives.

Just curious, why not? I don't coat any of my blades. But when I did I used Vasoline. Mineral oil that actually sticks to the blade. Basically food safe and its cheap and readily available. Worked great, but I like a patina, so I stopped using it.

You're right that nothing wrong with it safety wise. Just thicker than I'd like. I'd just use a really light coat of laxative grade mineral oil. But I honestly don't even do that and that includes some pretty reactive kitchen knives.

[On Edge]

Thanks for the advice.

I first heard about Bar Keeper's Friend on this forum, but I've never come across it before. Where is that stuff available? I suppose you can probably get it on Amazon.

I found it in Lowe’s with the cleaning products - I use it to clean my Sharpmaker rods.

[JSumm]

Make a paste out of a little Bar Keeper's Friend powder and water or baking soda and lemon juice if you can't find it and rub on the orange spots. Give it 30secs or so and then scrub with a sponge. See if that gets it.

I wouldn't use Vasoline on my knives.

Just curious, why not? I don't coat any of my blades. But when I did I used Vasoline. Mineral oil that actually sticks to the blade. Basically food safe and its cheap and readily available. Worked great, but I like a patina, so I stopped using it.

You're right that nothing wrong with it safety wise. Just thicker than I'd like. I'd just use a really light coat of laxative grade mineral oil. But I honestly don't even do that and that includes some pretty reactive kitchen knives.

I gotcha. That makes sense. I used to wipe it down pretty good so there wasn't any large amount left. Even after wiping it down the wax really helped it stick. However, I just stopped using it and appreciated the steels like K390 for what they are. And their wonderful patina.

[On Edge]

To the OP’s original question … generally a patina serves to help prevent red rust from forming. I’m sure smarter folks than I will chime in and explain why that type of oxidation prevents (or forestalls) further corrosive action, but much of my collecting involves traditional folders which for the most part are high carbon steels. I cannot remember any knife of mine that formed a patina ever rusting … but that’s just my experience.
Edited to add: what I’m referencing is patina on the blades. I keep my hinges and back springs well oiled/coated either with Tuff glide or mineral oil. Aside from the occasional pepper spots that’s worked for me for 20+ years.

[Bolster]

When does patina become rust? Easy.

Patina is what I get on MY knife.
Rust is what you get on YOURS.

[Evil D]

Patina is oxygenation on the surface of the steel, rust is the degradation of the steel itself. At least that's how I make sense of it. You can polish off a patina but rust involves pitting and loss of steel.