Garlic Tarnish?

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fib45

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Jul 23, 2018
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Hey all. I've only made a handful of knives so far and have only done a couple made with any steel of worth. I've been working on a kitchen knife out of a saw blade and before I finished the edge I wanted to feel the basic geometry of it so went into the kitchen and diced some garlic.

After a few minutes I noticed the edge side was developing a tarnish. It does not wash or scrub off, but I am sure it would come out with a little more hand-sanding (yayy).

Has any one seen this before? Any chemists out there that have any ideas? I'm mostly just curious as the rest of the internet has not helped at all so far. Thanks!
(I have no idea how to upload photos but if someone helps me out I can show what I'm talking about.)
 
Yes, your knife has developed a patina. All carbon steel blades will do this when they come into contact with the various chemicals in foods (usually acidic). Apparently garlic is moderately alkaline - but it will certainly cause a blade to patina, as will onions, which are highly alkaline. Can't help you with the science of it.

Fine sand paper will remove it in no time.

Edit:
Depending on the look you're going for, you might just want to leave it. Patinas offer some protection from rusting, since they are a stable oxide layer on the surface of the blade. You can also intentionally patina a blade with mustard (among other things) to get interesting effects. This is a blade I did a while back with a mustard patina:

https://i.imgur.com/ASAEoxG.jpg

https://i.imgur.com/xdyojRr.jpg
 
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The onion family all have mercaptans which are organo sulfer compounds that give those plants the pungent flavor and aroma. The black on the steels is a sulfur compound.
 
mete said:
The onion family all have mercaptans which are organo sulfer compounds that give those plants the pungent flavor and aroma. The black on the steels is a sulfur compound.
Click to expand...

Thanks, Mete! Is it just iron sulfate - or is a complex of different stuff?
 
Iron sulfate.
Some folks rub an onion all over a new blade to patina it dark. Others use a lemon. Most just let it darken on its own. The patina is beneficial, and is normally a desirable thing in carbon steel kitchen knives.

The patina is only a few millionths of an inch deep, and can be removed by rubbing with steel wool or fine sandpaper. Polishes, like flitz, will also remove it.
 
Edit:
Depending on the look you're going for, you might just want to leave it. Patinas offer some protection from rusting, since they are a stable oxide layer on the surface of the blade. You can also intentionally patina a blade with mustard (among other things) to get interesting effects. This is a blade I did a while back with a mustard patina:

https://i.imgur.com/ASAEoxG.jpg

https://i.imgur.com/xdyojRr.jpg[/QUOTE]

Love the look of that patina. How did you get it?
 
Folks have experimented with different foods to see which gives the best looking patina in their opinion. Mustard is quite popular. I have heard some say that slicing raw beef will give you that cool blue patina with some steels.
 
Beef - it's blood contains hemoglobin [red] which is a complex molecule containing iron .That's why blood will help form rust on the blade !

Garlic has been used in medicine for a very long time !
Gardiners use it to kill fungus .
 
My favorite Aging/patina (though you have to be careful about etching depth on kitchen knives) is to coat the blade in a selenium dioxide solution (most steel 'cold blues'), let it dry and dunk the blade into chlorine bleach (outside, and do not breathe in the fumes). As you get comfortable with the deposition of the selenium dioxide, you can do some really awesome patterns, age nicely, etc.
 
What are people's feelings on new kitchen knives with forced patinas. I have done a couple with a FC patina and then brought it down to a mild tint with a finer grit and it seemed to patina more evenly than others. I'm not sure if that's how it worked or if it's just how those turned out.
 
I force a patina on almost all of my kitchen knives. Often via a proper acid etch, but I also use mustard, the technique previously described, jax's, and a recent favorite blackening technique.

The newly discovered blackening technique combines a traditional blackener like Jax's and a rust brown (I use plumb brown) I have been playing with this for a bit and I get better results if I use a blackener first. Basically, after application of the blackener I torch heat in the mid 200s F and then apply a rust brown. I then steel wool the rust off and I am left with a very deep matte black finish. I get deeper, more consistent blacks by applying a blackener first, but I am still experimenting (may be possible with repeated applications of the rust brown). There is an intermediate golden/orange color that occurs during this process (it is a really cool color, not that of a straw temper) that I have only been able to achieve on portions of the knife. Would be cool for a more mottled finish, but I cant get it to consistently cover the blade.

On the whole, I am entirely in favor of a forced patina on carbon steel knives. They will end up with one either way, so I prefer to save the effort of a mirror polish and add a patina that will last.

The one area I try to shy away from is particularly deep etches that may harbor bacteria or make the knife more difficult to clean. While I fear no bacteria personally (I think most of the bacteria based food safety stuff is bunk - I can go farther into this but ultimately we have gone way past food safety to the point of detriment), I try to ensure any knife I make (at least for distribution) has no deep etching or other area that would make it unacceptable for a commercial kitchen. My exception to this is that I will happily make wood handles for gifts or if requested.

Incidentally, many of the commercial regulations suck, but if you got a buddy or client in that industry, don't be the reason they get into trouble.
 
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