Coffee Stains

[mrwizard]

Since I'm notorious for leaving coffee stains everywhere, i felt challenged when i read on a knife-makers forum that coffee gives good contrast on damascus.
So, i selected a Bali tourist/soldier keris, i couldn't successfully stain with FeCl3, and made a lot of coffee....

First i followed the instruction given on the other forum and prepared the coffee with two spoons of instant-coffee per 200mL of hot water. Meanwhile the keris is degreased and etched for 2-5min in citric acid. The keris is then fully submerged in the still hot coffee. The pamor became visible after 2h and reached its maximum contrast after 6h. The result was rather disappointing. After drying the pamor was barely visible.

Next i repeated the procedure with "real" and strong coffee. That lead to the same result after 2-3h.

For the final experiment i added a teaspoon of citric acid to the coffee (about 4L). This gave a remarkably good result after about an hour (see photo). Leaving the keris longer in the coffee proved counterproductive as the contrast began to degrade after the coffee cooled down.

After the promising results i tried to stain the keris from this thread http://www.vikingsword.com/vb/showthread.php?t=13829
with the same mixture. However, this time the result was very poor.

Conclusion: Coffee may for some keris be a viable alternative to FeCl3 but may fail miserably on others.
For good results the coffee has to be hot and slightly acidic.

Best Regards,
Thilo

[David]

Since i LOVE coffee i also love this idea. Too bad results aren't consistent (though the results in the photo here look fairly decent) . I guess i'll stick to just drinking mine...
BTW, i like your "coffee stirrer"...

[rasdan]

Hello Thilo,

That's an interesting experiment. I'm not a chemist or a keris professional, but I think what happened is by adding citric acid to coffee (acidic) you are actually increasing the acidity of the solution hence giving you the stain.

Coke are more acidic than coffee, perhaps it (+add some more citric acid) will give a better stain? If not, there's gotta be something in the coffee.

Also, perhaps you would like to compare your current staining result with a stain using 4L of hot plain water and 4 tablespoon of citric acid maybe? I used this solution to clean keris and sometimes it also gives a bit of reasonable staining to some keris.

I'm thinking of adding some sulphur (which can also stain) in the solution in the future, but normally to get sulphur easily mixed in the solution we need to add a bit of salt. The salt part is the one that worries me.

[mrwizard]

Hello Rasdan,

I cleaned this keris with citric acid, so i know what this looks like (a dull grey). Even without citric acid the coffee stained darker. That's the reason it is preferred by knifemakers (who can of course select the steels they are using).
However, I'm not sure what reaction causes the coffee to stain the iron. Main reagent is most likely caffeic acid.
The reaction needs more activation energy than citric acid as it works only when the coffee is hot. The citric acid seems to somehow speed up the reaction. I think when the solution cools down the citric acid becomes the dominant etchant again and slowly degrades the coffee-stain. At least the stain becomes dull grey again after a few hours.

The main reagent of cola is Phosphoric acid. It transforms red iron oxide into black iron phosphate. So it may indeed work. But i am concerned about the sugar. I don't want a sticky keris... ;-)

btw. i'm no chemist either and i guess "keris-professionals" would either use arsenic or have their keris stained professionally

Best Regards,
Thilo

[A. G. Maisey]

I have not heard of using coffee as a staining agent on mechanical damascus. Interesting.

I've made and stained a lot of mechanical damascus, based on iron or mild steel and 01 steel, sometimes with the addition of nickel. I have usually stained this with ferric chloride, but on occasion I have used other acidic substances such as dilute hydrochloric acid, or ordinary household vinegar.

To test the efficacy of a staining agent it is necessary to begin with new material to be stained, if you do not begin with a new blade, you are not testing the staining agent, you are testing the blade.

With old keris blades, I have had satisfactory results using a variety of staining agents, it seems as if almost any acidic agent will give some sort of result on an old blade, with the result depending more on the blade than on the staining agent. However, the only consistently good results that I have ever achieved have been with arsenic, in one form or another.

[rasdan]

Hi Thillo,

Sweet.. So it's something in the coffee Higher acidity does not mean better staining obviously.

I always wondered on what exactly happened chemically we when stain a blade and what is the main substance, but I never ventured into finding the answer.

G'day Alan,

Do you have any suggestions of other solution that can be used to stain wootz? I have some difficulty in finding FeCL3 here in Malaysia. I am considering of using coffee now.

[milandro]

Originally Posted by mrwizard

Since I'm notorious for leaving coffee stains everywhere, i felt challenged when i read on a knife-makers forum that coffee gives good contrast on damascus.
So, i selected a Bali tourist/soldier keris, i couldn't successfully stain with FeCl3, and made a lot of coffee....

First i followed the instruction given on the other forum and prepared the coffee with two spoons of instant-coffee per 200mL of hot water. Meanwhile the keris is degreased and etched for 2-5min in citric acid. The keris is then fully submerged in the still hot coffee. The pamor became visible after 2h and reached its maximum contrast after 6h. The result was rather disappointing. After drying the pamor was barely visible.

Next i repeated the procedure with "real" and strong coffee. That lead to the same result after 2-3h.

For the final experiment i added a teaspoon of citric acid to the coffee (about 4L). This gave a remarkably good result after about an hour (see photo). Leaving the keris longer in the coffee proved counterproductive as the contrast began to degrade after the coffee cooled down.

After the promising results i tried to stain the keris from this thread http://www.vikingsword.com/vb/showthread.php?t=13829
with the same mixture. However, this time the result was very poor.

Conclusion: Coffee may for some keris be a viable alternative to FeCl3 but may fail miserably on others.
For good results the coffee has to be hot and slightly acidic.

Best Regards,
Thilo

when I got my first kris I tried the coffee method and results were actually quite good , later on I did have this kris etched with traditional warangan and the results were better but not spectacularly better.

Then I tried the same thing on two KNIL soldiers krises made in Madura , coffee did absolutely NOTHING there just literally a stain which could be washed off with water.

[Battara]

Any pictures?

[milandro]

unfortunately not , I've kept a couple for a while of this experiment on my phone but then I erased them at some point.

I guess that it depens on the metals involved.

Perhaps one of the so many videos on your tube would inspire someone

https://www.youtube.com/watch?v=inGtEynlP0E&t=1215s

It clearly is not one easy thing

[A. G. Maisey]

Absolutely first class.

Thank you Milandro.

[kronckew]

Apparently Instant coffee is more acidic than fresh ground coffee.