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Gerhard Gerber

Coffee etch inconsistencies

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I gave a friend the advice to do a coffee etch on the cleaver I made for him to prevent rust.

The cleaver came back to me last week for a Kydex "saya" to make sure nobody looses a finger in the cutlery drawer......and I was blown away by the results of his etch! Black as night! B)

One of my knives is going to a professional hunter next week, I know blood will be involved so with his blessing I did a coffee etch.......after adding lots of fresh coffee powder to my ready mix.

Left it overnight and got a nice dark patina, except for a few completely untouched splotches! :angry:  I washed the blade with warm water and soap before the first etch, got rid of most of the patina when I washed it again, concentrated on the untouched parts with the scrubber and made sure I don't touch the blade.

Next morning the etch was ever darker, no splotches, but the edge and the corners of the spine does not etch!

It does not look good, so I have to clean up that mess and give it an even finish very quickly......leaning to cold blue despite the fact it's not durable on 5160.

Any idea what is going wrong?

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Did you use very high concentration of instant coffee?  Clean your surfaces with a solvent (acetone or the like) before etching?  Are the edge and spine corners significantly more polished than the other surfaces being etched?

For what it is worth, I don't like to etch after final sharpening as I believe that if the etch is effective it must also remove something from the blade edge as well, potentially blunting it a little.  I like the contrast of the polished edge with the etched surface I get from doing my final sharpening after etching, but understand that it might not be to everyone's taste.

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On 9/19/2019 at 6:14 AM, Dan Hertzson said:

Did you use very high concentration of instant coffee? 

My mix is generally about 3 tablespoons to 16 oz. of water. So, yes high concentration is a must.

On 9/19/2019 at 1:59 AM, Gerhard Gerber said:

after adding lots of fresh coffee powder to my ready mix.

I mix it up fresh every time.

On 9/19/2019 at 1:59 AM, Gerhard Gerber said:

but the edge and the corners of the spine does not etch!

Thin tight radii will take etch less than flat surfaces. This will clean off easier.

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Joshua, do you mix the mixture of Instant coffee with boiling water or do you use cold?  This is the first time that I have heard about using a coffee etch. It seems some people use it on Wootz as well with success. 

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On 9/21/2019 at 7:42 AM, Tim Mitchell said:

Joshua, do you mix the mixture of Instant coffee with boiling water or do you use cold?  This is the first time that I have heard about using a coffee etch. It seems some people use it on Wootz as well with success. 

Sorry it took so  long to get back to you Tim. I didn't realize you had asked me a question.

Boiling water. I let cool to a temp not uncomfortable to the touch and soak the blade for several hours. Sometimes even overnight. Most of the time, I will then go back and apply cold bluing. This also helps with Gerhard's edge and corner problems. The cold blue covers those bare spots and blends in well enough that they become unnoticeable.

My Results can be seen at the end of this thread.

Edited by Joshua States
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Gerhard,

 

It sure sounds as if the surface of the steel wasn't cleaned completely.  I do all  of my coffee soaks after coming out of a ferric etch.  When you take the blade out of the ferric DO NOT USE ANY CLEANERS OR SOLVENTS.  Don't wipe off the ferric with a rag or paper towel.  Merely rinse in clean water.  If the ferric etch is uneven, rub the blade with a new  piece of 0000 steel wool until clean and repeat the etch.  Once again do  nothing to the blade after the ferric etch but rinse in clean water and place the blade into the coffee.  If you have an even ferric etch, you will get an even coffee etch. 

When I make my coffee etchant I put an entire 14 oz. can of instant coffee into one gallon of water.  I use a one gallon mason jar which gives me enough depth for most large blades.  I can use the same coffee for months at a time.  There may be some mold form on the surface  occasionally but simply scrape it off and return the cap.  It won't ruin the coffee.

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Thanks Joshua, I will have to play around with this a bit.  I loved the blade in that thread... very nice pattern and the coffee etch really is startling in it's contrast.  I also like the comments about normalising and graphite spray to remove the lines... Were the lines due to decarburisation of the outside of the bars while welding? That is what it looks like to me..

Gary thanks for the info on your method too... I like the idea of going straight from the ferric into the coffee without cleaning the blade... it makes sense.

 

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Thanks for the advice, I had a long weekend in the desert and knew I would run out of time so I bought some cold blue and used that.

Not durable at all on 5160 but I know as well that if the knife gets used a natural patina will just replace the blueing.

I did wash the blade with hot water and soap each attempt, and I tried Acetone as well......one drop was enough to discolor the micarta :angry:

Gary - thanks for the Ferric etc tip, I did not think of that.  There are several reasons why this would have been difficult to do on this completed knife, but I will not mention then since that would simply highlight things I know are still wrong with my process :D

My friend also confirmed he just used a whole can of instant coffee for his cleaver.

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8 hours ago, Tim Mitchell said:

Were the lines due to decarburisation of the outside of the bars while welding? That is what it looks like to me..

That is what most smiths I talk to believe is the case. It makes sense because the graphite/normalization techniques really only serve to make a little extra carbon available and encourage carbon migration.

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Different steel so not really relevant to this topic, finished up two pretty little kitchen knives forged from a bearing race, briefly dipped it in FeCL, cleaned them up and into the coffee.

The finish is nice and even as well as durable.

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