Iron Tsuba With 'old Silver' Patina

[JohnTo]

Happy New year

I have recently bought an iron sukashi tsuba with an unusual patina that I would like some opinions on (see three photos).  The tsuba is wakizashi size (6.3 cm, 5.7 cm 0.6cm) and nicely carved in the round and pierced with a pine tree design.  The nagako ana has scratches from a sword and punch marks indicating that this was once mounted, though the punch marks are often found on late tsuba purely as a form of decoration.  The tsuba is unsigned and my initial guess was that it is 19^th C Bushu or Echizen work.   However, probably it is a cast piece that has been finished off by hand as the form is similar to a 19thC cast and carved brass tsuba that I have (see photo of my example and see an identical tsuba on Ebay [Matsukage, Dec 2016]). 

The unusual feature of this tsuba is the patina, which is outside my experience.  It resembles  a piece of silver which has blackened with age but has been regularly cleaned with a cloth, resulting in discolouration only on the inner surfaces.  However it’s not silver, it is iron and magnetic (always good to check, I recently bought  tsuba from a major auction house that was described as ‘bronze’ but was magnetic).  Nor does it appear to be a case where the tsuba originally had a black patina which has worn away through use.  The effect is uniform over all the surfaces.  The piercings looked a little clogged and so I cleaned them out with a wooden tooth pick.  The black specks that were removed were also magnetic (probably magnetite, Fe₃O₄), possibly indicating that the maker had been a bit sloppy in removing all the scale.  The iron has no other traces of rust, except for bands of surface rust running along the mid sections of the piercings.  The tsuba looks as if it could have been made yesterday, but was part of a job lot of 8 iron and soft metal tsuba plus fuchi-kashira and menuki that I bought at an auction.  The lot looked like someone’s collection of better than average pieces from 17^th-19thC.

 

Looking closely, the shiny parts the steel shows a slight surface colouration that includes purple, steel blue, bottle green and copper red.  The sort of effect seen in tempered or partially blued steel.  I think that the patina is deliberate and original.  Normally I would be overjoyed at finding an iron tsuba in such pristine condition, but as it appears to have been on a sword I would have expected some evidence of corrosion, especially on the metal with minimal patination.  I have thought of the following possible reasons.  Comments please.

1. The tsuba is 19thC cast steel and subsequently carved and engraved by hand.  Any original black patina was deliberately polished off the outer surfaces to produce the effect seen today, possibly augmented by tempering at the final stage.  Subsequent owners of the tsuba treated it with great care and hence prevented corrosion.
2. The tsuba is 19thC as reason 1, but was made of a non-corroding iron/steel.  Proper stainless steel, with at least 10.5% chromium, was not invented until 1911.  However, Stoddard and Farraday in about 1820, noticed that low chromium iron alloys were less liable to acid attack.  Perhaps some enterprising Japanese tsuba maker was experimenting with new iron alloys from Europe or the USA?    Apparently 0.1-0.4% copper, or 10-20% nickel, also improve the corrosion resistance of steel.  Unfortunately, I do not have access to a X-Ray Fluorescence (XRF) spectrometer (unlike Ford Hallam) and hence cannot determine if other metals are present.  Nor am I going to wrap the tsuba in a cloth soaked with saline and leave it for a month to see if it really is corrosion resistant.
3. The tsuba was made in the early 20thC out of stainless steel, or some such alloy, possibly for use on a gendaito in a moist environment, e.g. jungle.
4. It’s a completely modern tsuba that the previous owner of the collection picked up somewhere, simply because he liked it.

Best Regards, John

[Brian]

Why not just a regular iron tsuba that was chemically stripped and the attempt at repatination has not taken or been done?
Looks like the finish was stripped to me.

[Ford Hallam]

I'm with Brian on this one.

 

In fact, you provided the evidence very clearly in you own words, John. :-)

 

The most obvious and easily understood (by the layman) bit of evidence is this;

 

The piercings looked a little clogged and so I cleaned them out with a wooden tooth pick.  The black specks that were removed were also magnetic (probably magnetite, Fe₃O₄), possibly indicating that the maker had been a bit sloppy in removing all the scale. 

 

 

 

 

 

 

There you have it. It did have a patina. Magnetite is a major component of ferrous tsuba patina. That is came away on a toothpick is a clear indicator that the original patina was stripped using a mild acid or de-oxidising solution.

 

The iron has no other traces of rust, except for bands of surface rust running along the mid sections of the piercings.

 

 

Bands of rust...ergo; not likely rust resistant or stainless. And the banding points to a layered structure consistent with folding.

 

I would add that the sort of iron used for these types of tsuba was essentially a very finely worked 'wrought iron'. One of the interesting and useful features of this material is it's inherent corrosion resistance compared to a more homogeneous mild steel or simple carbon steel. This is generally understood to be a consequence of minute fibrous traces of silica and slag that inhibits the usual action of iron being converted to iron oxides, rust.

[JohnTo]

Brian/Ford Thanks for the info.  I think you are right

The band of rust and magnetite crud in the piercings was saying ‘Genuine’, but the patina and lack of corrosion was shouting ‘Wrong’.

While puzzling over this tsuba I had a break to make a cup of tea and as I fished the tea bag out of the cup with an old stainless steel spoon there was a similar patina staring at me.  The spoon had acquired a blue colouration from the dishwasher.  Hence my wondering if it was a type of stainless steel, rather than wondering if samurai used dishwashers to clean their tsuba.  I was also concerned about the complete lack of any evidence of corrosion (rust or pitting) on the main body.  As the old saying goes ‘If it looks too good to be true, it probably isn’t’. 

This tsuba was different and probably had a uniformly black patina originally, which I guess had become worn through in places (based upon limited observations in my collection, black patination does seem subject to wearing away in places). A previous owner probably cleaned it with acid to remove the patina, using a cloth rather than soaking, which only removed the patina from the high points.  He probably attempted to restore the patina by tempering (hence the multi coloured effect).  Maybe he should have invested in a can of gun blue.  I came across some (once) nice Kyo sukashi tsuba at an auction about 10 years ago.  They had obviously been soaked in a commercial (phosphoric?) acid cleaner and rust proofing agent that gave them a dull grey colour and still left the pitting.  I was outbid and the price they went for indicated that the buyer thought they were restorable.

I suppose I could have the tsuba repatinated  professionally, but to be honest, I quite like the effect.  The remaining black patination in the indentations and sunken carvings has produced a pleasing 3-D effect which may be lost with a uniform black colouration