Coffee Stains

[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.

[A. G. Maisey]

Bill Moran

http://en.wikipedia.org/wiki/William_F._Moran

used hydrochloric acid, as I did myself until I discovered ferric chloride.

In fact, dilute hydrochloric acid , and virtually any other acid, if handled correctly, will give a more realistic and subdued stain than ferric chloride.

If you need a topographic etch before you stain, hydrochloric acid is probably better for this, but in my opinion the nicest finish to damascus is a very light etch that leaves you with a smooth polished surface and a subdued stain, rather than the in-your-face high contrast that most knife show buyers seem to prefer.

[mrwizard]

Hello Alan,

i was also surprised that coffee is frequently used for that purpose. I guess the reasons are is that it is readily available, requires no safety measures, and can be disposed off in your kitchen sink.
Of course results are more consistent using new blades with well defined steel combinations (e.g. 1.2848 and 75Ni8).
Nevertheless, i thought i would give it a try and share the results

@Rasdan
Buying a ton of FeCl3 would probably be no problem anywhere in the world (especially in Malaysia with its electronics manufacturing industry), getting it in small quantities is more difficult.
Here in Germany FeCl3 is available in small quantities at electronics retail stores for PCB etching. But with PCB services becoming less expensive this is a dying hobby. I don't know if there are such store in Malaysia, but i am sure these guys know if there are: http://www.marts.org.my

Best Regards,
Thilo

[rasdan]

Thanks Thilo and Alan!

[kai]

Hello Rasdan,

Wootz and pattern welded blades can require pretty different approaches to etching. Granted, also pattern welded pieces can easily damaged by overenthusiastic staining attempts but etching wootz (especially antique pieces) is even more an art. If you really need/want to etch wootz yourself, make sure to search for similar blades (origin and age and wootz type) which are still in stain as a reference. While FeCl3 can be utilized to etch wootz this is by no means the only nor likely to be the single best approach for the majority of antique blades. There's a lot of other etchants which may be suitable or a combination of these may be needed for optimal results (quite a lot of pointers and opinions can be gathered from the net). I'd certainly recommend to try very weak dilutions first even if this needs more patience. If the wootz blade has still a nice original surface which hasn't been polished with power tools, diluted oxalic acid may be worth trying first - just a wild guess though.

Regards,
Kai