Coffee Staining Question

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VorpelSword

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I have seen a few forging videos where one of the final finishing steps is to soak the blade in strong coffee to darken it.

Whiskey Tango . . .how does coffee react with the steel? I mean I understand etching and bluing, what is going on with coffee?

Does this treatment last or can it fade if left in a display case (or my sock drawer)?

Is there any adverse effect on the steel over a extended period of time?

This treatment is not traditional to knife making, only coming out in the last ten years or so I think. I wonder why it never occurred to anyone to treat steel this way before in the several thousand (hundred?) years we have had both fine steel and strong coffee.

I am just trying to understand the treatment, not knock the practice.
 
The coffee leaves a resinous layer on the steel. It doesn't actually darken the steel itself. It will rub off with use.

It is a fad thing, IMHO, that will be popular with shelf queens, but not users. I don't see future archeologists recovering 21st century knives with this still on them.
 
Stacy E. Apelt - Bladesmith said:
The coffee leaves a resinous layer on the steel. It doesn't actually darken the steel itself. It will rub off with use.

It is a fad thing, IMHO, that will be popular with shelf queens, but not users. I don't see future archeologists recovering 21st century knives with this still on them.
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Now that's a hot take!

For what it's worth, I don't think it's a fad at all. Whether or not future archeologists will be recovering coffee etched knives or not, I think it's a valuable tool that will be sticking around. It works quite well, at least on carbon steels, and holds up just as well as ferric chloride for normal use at least on kitchen knives. I think one of its biggest advantages is how approachable it is even to a home user. Maybe someone wants to thin out a knife that's been sharpened a lot over the years, but doing so will ruin their nice finish on the blade. With a coffee etch they could easily thin it out on stones and then re-etch in instant coffee. In fact, I just posted a thread a few minutes ago basically asking about this exact scenario but on stainless damascus and muriatic which is a lot less user friendly. Just my 2 cents. (Or maybe 4 cents adjusted for inflation.)

But I have no idea to the exact answer to the OP's question about how it works exactly, sorry.
 
Stacy E. Apelt - Bladesmith said:
The coffee leaves a resinous layer on the steel. It doesn't actually darken the steel itself. It will rub off with use.

It is a fad thing, IMHO, that will be popular with shelf queens, but not users. I don't see future archeologists recovering 21st century knives with this still on them.
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And that must be why this treatment is not used to darken the blades of "tactical" knives.
 
VorpelSword said:
And that must be why this treatment is not used to darken the blades of "tactical" knives.
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There are many different options for blades where food safety concerns are not an issue. I use Gunkote bake on ceramic paints from KG industries in texas if I need/want a permanent black.
 
I did an AI search on coffee etch durability using this thread as a starting point. This was the result of 606,000 hits:


606,000 results
Result - Not very durable
Coffee etching is a method that uses the natural acids in coffee to create a distinct, vintage patina on steel knife blades4. However, it is not very durable and will rub off and scratch easily. For a more durable dark surface, consider other treatments like Parkerizing or epoxy blade coatings

Also, these older thread:
https://www.bladeforums.com/threads/coffee-etch-clarification.1627024/

K

Thread 'Coffee etching??'

Hello! Im working on a chefs knife made with 1095 and as I am sitting here waiting on clay to dry for a hamon, I ran across something Ive never heard of before. Coffee etching! But I cant find much info about it. My question is does anybody here know if this will work on 1095 and will it bring out the hamon??
If so does anybody know the process and or how to make the coffee etching solution?

T

Thread 'Strange colors after coffee etch'

https://imgur.com/a/I817xHY

Got these strange colors after a coffee etch. Steel is 8670, it was first etched in ferric chloride, then I put it in an instant coffee mix for a few hours following instructions I found through YouTube. Anyone know what could have caused this coloration? Looks like a knife that was put to temper in an oven that still had oil on it. The steel was cleaned appropriately before the ferric and before the coffee. The ferric etch was completely normal so it had to be something with the coffee I assume. Any ideas?
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as an occasional user of damascus knives in a fairly 'hard use' setting, I can tell you that no black etch is durable. The difference between ferric chloride and other things is how deeply the acid penetrates, from what I can tell. The raised surface of the bright steel might protect the lower darkened surface somewhat from buffing off, but that surface oxidization is not durable.

etch a knife completely black with your choice of etchant, then go chop some bushes or wood with it and you'll find it rubs off pretty quick.
 
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What does a damascus blade ready for etching do when held in "coffee etch" without a prior ferric chloride etch? Does it etch like ferric chloride does? Will it eat steel away? Anyone have any idea of the pH of their coffee solution? Normal coffee is around pH 5.
 
fitzo fitzo I think etch is the wrong word for the coffee treatment. I would describe it as a way to set and accentuate the oxides produced in an acid etch.
I started a thread in 2018 when I made some handle fittings from stainless damascus and couldn't get a good contrast. (this was prior to hardening) I tried the coffee also with no effect. After hardening I got a decent contrast.

None of my efforts with stainless damascus produced the dramatic contrast you see from people like Royer and Straub, who use non-stainless like 15n20/1080. I recently made steak knives with some of this material from Straub. I could immediately see why they like it from a visual perspective. In just a couple quick FC etch cycles, I had way more contrast than I've seen before and topography that you can feel passing your fingers over it. I did the ultra strong instant coffee soak and it dramatically darkened the blackened parts. I was suspicious that it would just wash off, but it's remarkably resilient to fairly vigorous scrubbing. I expect that used as steak knives and hand washed, they will maintain their appearance for quite a while.

Unhardened stainless damascus
C3DjpKr.jpg

Hardened stainless damascus
8SYLaw7.jpg

15n20/1080 ferric only
PXL_20241204_231132014~4.jpg

15n20/1080 ferric plus coffee
PXL_20250105_174955932~2.jpg
 
Thanks for your response, Richard! I rather suspect it is more like a "coffee stain" than an actual acid etch, a reaction with existing oxides. It is interesting that it sets up well and holds. It would be interesting to get it in a lab with some good microscopy probes and find out if it is a physical adhesion or chemical reaction.

Lovely steak knife set, BTW!
 
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I think that the coffee etch started out as a food safe etch on culinary knives.

Step 1: etch blade in ferric chloride

Step 2: finish blade to 1200-2500 grit

Step 3: etch in very strong instant coffee

I attended a hammer in once where Don Fogg was teaching. He liked his coffee and drank it throughout the day. Someone put some ferric chloride in a styrofoam cup so he could test etch a small tile. At one point he grabbed the FC and took a sip mistaking it for coffee. Luckily, he’s still with us.

Hoss
 
Just to be clear, a coffee "etch" works. A while back, I was asked as a chemist to do some research on a coffee etch for a FIF blade. Here is what I found:

Basic info - Lower layer count damascus works best. On a mono-steel blade it can scratch and wear quickly. Bold patterns, like crushed W's, feather, and mosaics look the best, as Richard's photos show. Etch deeply with FC first.

PROCEDURES and PROCESS:
1) The coffee does not etch - The FC does that. Etch in FC as usual and clean/neutralize the blade before the coffee etch. You can polish the high spots now, or leave them for after the coffee soak. Etching a little deeper than normal gives a deeper recess for the coffee varnish to fill.
2 The organic acids in the strong and hot coffee reacts with the steel's surface after the FC etch and creates an organic compound with the iron in the steel. This is similar to the black compounds formed by tannins reacting with iron in other types of organic etchants and stains. Basically, the coffee creates an organic varnish.
3) Any coffee will work, so most folks use the cheapest instant coffee they can get.
4) Brew the coffee as strong as it will dissolve. Just keep spooning more in until it won't dissolve any more in near boiling water.
5) Suspend the blade upright in the coffee mixture and soak at 160-180°F for 4 to 6 hours. Hot coffee will make a much better black color. An enamel coffee pot is perfect and can be heated on a hotplate or stove. A stainless container will work. Glass will also work, but glass breaks.
6) Once the soak is finished and the black looks sufficient, rinse lightly ... do not scrub off ... and cure in a 250°F oven for an hour.
7) Use a hard backing block and very fine paper ... 1000 grit or higher ... to brighten the high relief of the damascus, leaving the coffee varnish in the recesses.
8) Buff lightly with a soft polishing cloth if desired.

Nerd info:
The organic acids in hot coffee are - malic, citric, acetic, phosphoric, and chlorogenic acids. The chlorogenic acids break down into quinic and cafeic acids. None of these are strong enough to eat away steel to any degree. They make coordination bonds and create positively charged ionic compounds. These positive organic ions will combine with the negatively charged iron ions (given time and heat) to make a stable black compound that bonds to the carbon steel blade surface. Ingredients in the steel like nickel and chromium will deter the bond from forming.
 
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weo said:
it's my understanding that the cheaper and worse the instant coffee, the better...
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This is my philosophy as well actually. Not for staining knives, but for drinking. ;)

But to the point: I did what I thought was an "instant coffee patina" on a few 1095 blades I had a back before I was a maker on Bladeforums, and I liked the outcome.
 
DevinT said:
I think that the coffee etch started out as a food safe etch on culinary knives.

Step 1: etch blade in ferric chloride

Step 2: finish blade to 1200-2500 grit

Step 3: etch in very strong instant coffee

I attended a hammer in once where Don Fogg was teaching. He liked his coffee and drank it throughout the day. Someone put some ferric chloride in a styrofoam cup so he could test etch a small tile. At one point he grabbed the FC and took a sip mistaking it for coffee. Luckily, he’s still with us.

Hoss
Click to expand...
Holy cripe!
 
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