Cleaning Rust From Heianjo Tsuba

[Ford Hallam]

Jean, Ken

 

The issue you both seem to be referring to is probably this. Most natural waxes and organic oils will in time break down into fatty acids. This process is in fact accelerated in the presence of copper as the copper acts like a catalyst. These fatty acids then act on the copper and any zinc in an alloy to form corrosion products called copper or zinc soaps. The copper soaps are green and the zinc is white. These are not sulphides but rather copper and zinc carboxylates.

The safest way to treat these soaps, particularly where they may have developed due to oil breakdown, would be to use a solution of white spirit and ethanol, 90:10 ratio. I’d use a cotton bud/earbud, dab lightly to soak the encrustations and then gently work at it with a wooden toothpick.
Wash in warm soapy water once the job’s done and dry well before re-waxing with Renaissance  wax.

I must credit, Francesca Leavey, who’s finishing up her graduate studies in metal conservation at West Dean College for the sciencey stuff here. Francesca recently did a 6 week internship with me which developed into a very exciting collaborative project that allowed us to investigate a number of such metalwork restoration and conservation issues that have a direct baring on tosogu. More on all of that in the near future.

 

edit to add; zinc carboxylates don't pose a health risk but the copper may be toxic, depending on exposure. Fine corrosion product dust can cause lung and eye irritation. Also, as the solvents used are volatile they should be used in a well ventilated area. Rubber, latex or nitrile gloves and a suitable dust filter mask is probably advisable.
 

[Ken-Hawaii]

Ford, the only problem with this theorem is that the change happened literally overnight. The tsuba sat on my dining room table, & it was a very-standard Heianjo inlay at 11 PM, but at 8 AM the next morning, the inlay was/is green. The only difference that I'm aware of is the heavy SO2/SO4 vog plume from the volcano - other than that, the tsuba sat in the same place for at least a week while I was using the ivory piano key to slowly remove the rust. The carbonates & acetates that I'm familiar with are rather "crusty," whereas the green sheen I'm seeing looks like a perfectly-smooth layer of transparent green.

 

On this side of the pond, "white spirit" is known as "paint thinner," & is a solvent that I haven't yet tried. I'll mix some up with ethanol in the morning, & apply it with a Q-Tip (earbud). Wish me luck! And thanks for weighing in! I'll certainly let you know the results.  (Maybe I should try  , too!)

 

Ken

 

[Ford Hallam]

Ken

 

Not carbonates or acetates. It's copper and zinc carboxylates, which are indeed characterised as having a waxy sheen. The fact that yours occured overnight doesn't rule them out, lab trials have in fact managed to get this process to happen as quickly.  If the corrosion was due to sulphides I'd

expect it to be blue or grey/black.

 

White spirit, mineral spirits, mineral turpentine, yes, all the same thing. Just make sure it's that and not some generic substitute called 'paint thinners' because the actual chemistry is important. Turpentine substities and the like won't work.

[Ford Hallam]

...could this be a form of verdigris? It is quite common in militaria where leather or canvas comes into contact with metal. One recommendation for removal is vinegar... but I am unsure if there will be any reaction with the surrounding metals.

 

[Ken-Hawaii]

Okay, Ford, if it's a carboxylate, then my lovely green film isn't reacting to the white spirit and ethanol, 90:10 ratio solute. Of course I had no idea that there are so many different formulations that call themselves "turpentine," & none that call themselves "white spirit," but at least the ethanol was easy. My wife (chemist) & I (chemical engineer) put together about a dozen small batches of solute using cotton towel swabs, but none had any effect, or at least nothing came off on the white swabs. I did try a touch of vinegar, but there was no luck there, either.

 

The green film is only on the one side of the tsuba that was face-up that night, so I guess that I'll just keep it under glass, with the other side up. If anyone has other ideas, feel free to post. Thanks!

 

Ken

 

[JohnTo]

You can heat the tsuba in a steam of dry hydrogen.  A heavily rusted viking sword was treated this way to reveal fine brass inlay (like a Heianjo tsuba).  Not a prcoess for the amateur collector though.  regards, John

 

Corrosion and metal artifacts - a dialogue between ... - NIST Page

nvlpubs.nist.gov/nistpubs/Legacy/SP/nbsspecialpublication479.pdf

CONSERVATION OF RUSTY IRON OBJECTS BY HYDROGEN REDUCTION. L. Barkman. 155 ...... Figure 4a. Hilt of a viking sword before hydrogen reduction ...

 

[Ken-Hawaii]

Not that I have any dry hydrogen lying around, & it's a pretty-involved technique, but that is a very-interesting treatise, John! I guess it proves that the federal government can occasionally do some useful work.

 

It'll be pretty heavy reading for non-engineers, but they definitely covered a lot of ground. Darn good find! Thanks! :beer:

 

Ken