Etching a blade with coffee?

This topic has 7 replies, 5 voices, and was last updated 12/18/2014 at 10:17 pm by Mr.Wizard.

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10/11/2014 at 11:25 am #20800
Mark76
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On another forum I asked the question how I should etch a laminated carbon blade (plain laminate, no damascus). Apart from the “normal” answer, with ferric chloride, I also got another answer: strong coffee.

At first I though this was a joke. Then someone provided a pic of a knife etched with coffee. I then thought it was a sediment of the coffee on the knife that darkened the blade. But then more people chimed in, with pictures, and told me the color change was durable.

Here are some pics from that thread (knives by Toni Oostendorp/Guido van Poppel).

A knife etched with ferric chloride:

The same knife, but now etched with coffee (rightmost knife):

Another blade etched with coffee:

Does anyone have experience with this? And what happens here chemically? Is it etching what happens or something else?

Molecule Polishing: my blog about sharpening with the Wicked Edge
10/11/2014 at 3:46 pm #20801
Daniel maloon
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Hey Mark, I’ve never tried coffee but have done this with the etching solution and also with vinegar. You can also use citrus or mustard. From what I remember it oxidized the metal in a different way than red rust does which attacks the metal.

-I should have known that is what you were getting at. Trying to find out what exactly occurs chemically with carbon and coffee would take more time than I am willing to give. Someone on here Will probably know. Maybe the guy spilt his coffee on his knife by accident and liked how it looked? That’s a nice looking Fujiwara.
10/11/2014 at 4:32 pm #20802
Mark76
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Thanks Dan. Yes, I’m familiar with forcing patinas. I’ve done it a few times myself. This is a Fujiwara carbon knife on which I forced a patina using mustard and vinegar:

Chemically spoken, a patina is caused by a redox reaction. Rusting also belongs to this category just as etching, which involves strong acids.

Coffee is acidic, but only slightly. A little more than cow’s milk, but less than beer:

So given the quite dramatic effect coffee can have, I wondered what is going on.

Molecule Polishing: my blog about sharpening with the Wicked Edge
10/12/2014 at 5:27 am #20814
Geocyclist
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I have never heard of using coffee. Mustard will go very dark. Lemon juice also dark, and vinegar is ok. I like rare steak the best. I don’t care for the very dark patina. Steak gives a mild to medium darkness and a slightly blue hue. It gives a natural look, aside from being blue.
10/17/2014 at 2:25 pm #20898
Mark76
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I got some information from a knife maker. According to him, Nescafe turns maganese into manganese sulfite, which is black. But he didn’t know what triggers this reaction.

Any chemists in the room?

Molecule Polishing: my blog about sharpening with the Wicked Edge
12/10/2014 at 4:19 pm #21905
CliffCurry
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Aloha Mark, I just wanted to say how smitten with the hues and speckled look of the patina on your Fujiwara I am… Any tips for a first timer to recreate this effect? I’d have a whole set like that if I could!
12/11/2014 at 4:22 pm #21922
Mark76
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Molecule Polishing: my blog about sharpening with the Wicked Edge
12/18/2014 at 10:17 pm #22113
Mr.Wizard
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I like the look of that dark etch. Can you describe (or link to) the exact process that was used for the first knife?
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