Black rust
 

I encounter this problem for nearly 40 years -- first with my early Colt automatic pistols, now with some of my keris blades: spots of black rust!

While red or brown rust usually comes off easily, black rust is very hard and very stubborn and seems almost impossible to remove. Is there any method to get rid of those ugly black rust spots? Any suggestion will be appreciated.

Regards,

Heinz

Black rust is caused by iron impurities that leaves too much sulfur behind
what causes the black spots.

I myself have tried various attempts to remove rust
(See the topic: cleaning the blade)
I had at that time only a blade with brown rust, but maybe this is a solution?

or you can try with :Oxalic acid :shrug:

found this:
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A simple and inexpensive way to remove rust from steel surfaces by hand is to rub the steel with aluminium foil dipped in water. Aluminium has a higher reduction potential than the iron in steel, which may help transfer oxygen atoms from the iron to the aluminium. The aluminium foil is softer than steel and will not scratch it, as steel wool will, but as the aluminium oxidizes, the aluminium oxide produced becomes a fine metal polishing compound.
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seems worth a try ;)

p.s. - black iron oxide is an alternative form of rust to the more destructive red rust we all hate. rust bluing is/has been used to produce a nice blue/black protective coating on steel, and the black ferrous oxide coating is somewhat protective against red rust, and is the major component in the patina steel aquires over the years. removal of black rust or patina from antiques may lower their value.

Aluminium foil in warm soapy water is the easiest way to clean silver cutlery --- beats silver polish any day of the week.

Sirek, Kronckew, thank you both for your suggestions.

p.s. - black iron oxide is an alternative form of rust to the more destructive red rust we all hate. rust bluing is/has been used to produce a nice blue/black protective coating on steel, and the black ferrous oxide coating is somewhat protective against red rust, and is the major component in the patina steel aquires over the years. removal of black rust or patina from antiques may lower their value.[/QUOTE]


I think it will be best to leave the "black rust" alone and just plane off the high spots with a brass scraper. My home-made brass tools have always been very useful for a gentle (red/brown) rust removal without harming the patina.

Heinz

dilute vinegar

Thank you, Kulbuntet. Would grapefruit juice or pineapple juice also help? Seems less aggressive to me than vinegar.

Regards,

Heinz

Hello Heinz,

You can always try. I prefer Diluted Vinigar for think black rust. And brush it away with a brass bursh. It works fine for me. The vinigar is not a strong acid, and les strong iff you dilute it a bit. It wil destroy the stucture of the rust, what you can bush of the next day.

Regards Abdulrahman (formerly Michel)

PS you can also have a look at this product. I realy works!!
Bio deruster link

Hello Abdulrahman,

Very interesting product! I think I'll try diluted vinegar first.

Thanks and regards,

Heinz

Hello Heinz,

what works fine and certain is lemon acid you can buy in the supermarket. I use a drain pipe closed at one side and hang the blade inside, when you contol it time by time the acid only destroy the corrosion. This blade for example is cleaned by lemon acid.

Regards,

Detlef

Hello Detlef,

Very nice result! I see that there are several options. I'll just have to try ...

I have always been very hesitant in using acidic solutions for cleaning purpose on metal surfaces. Being a long-time firearms collector, I believed in the formula
iron/steel + acid = corrosion.

The keris that I intend to clean is -- except for several black rust spots -- a very nice dapur Parungsari in a grey/white condition with smooth edges and beautifully executed luk rengkol. All I want is to preserve it in this shape.

Regards,

Heinz

Hello Heinz,

when you clean a blade in the way I have described and control it by time and don't let it to long inside only the corrosion going. I have cleaned many different blades like this and every time have had good results.

Regards,

Detlef

Thank you, Detlef. I think I'll try it coming weekend.

Regards,

Heinz

Hello Heinz,

Truth is, there will always be a bit of corrosion when placing iron/steel into acids - not that much of an issue with keris though if you're working with well diluted acids. Still, it's advisable to keep the exposure as short as possible by regularly checking the progress and frequently brushing the blade. The degreasing step should be done very carefully so that the acid can work evenly across the whole blade; also scraping thick deposits of rust/gunk off the blade with something safe like a piece of hardwood will help.

Pinapple juice works nicely and is supposed to be the gentlest of the fruit acids. If you have to work indoors with prolonged soaking times, the odors of the aged fluid may be a bit of a challenge though.

The advantage of acetic acid (vinegar) is that it is also acting as a vapor which seems to help reaching into crevices and loosening up tougher deposits. The active ingredient of several traditional cleaning solutions (like coconut "water") is acetic acid, too. Household acetic acid usually has about 10% strength while kitchen vinegar is around 4%. Check with the label and dilute to 0.5-1% for a start and go from there.

Regards,
Kai

Hello Kai,

Many thanks for the valuable information.

Regards,

Heinz

This weekend I cleaned a spotted keris blade by using diluted vinegar. It worked great -- all the black rust spots are gone! Thank you all for your advice.

Regards,

Heinz