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Shakudo


Mantis dude
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Hi all,

As I have been catching up on posts, I started thinking about a fuchi kashira I had. The f/k was black but had condition issues. It was cheap and I Sent it one of Ford's disciples to restore it. Turned out it wasn't shakudo at all, actually was copper and it didn't go back to black. The coloring formula lost to the ages (maybe). I use to think black = shakudo. With the f/k in mind , as well as, mino fittings that try to mimic shakudo I started thinking that there must be more out there. So my next question is how do you tell if it really is shakudo or not? Ignoring the shakudo quality subject unless relevant to the conversation. Any hints or suggestions would be much appreciated.

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What about Kuro-shibuichi as well. I have seen blueish/green "Shakudo" on a a very rusty/worn Tsuba(mimicing tree tops) that I don't know how it held up, the typical black and almost a deep midnight purple.

You say ignoring the Shakudo quality, are you referring to the gold content? From what I know the color of Shakudo is created chemically, and the color it turns is dependent alot upon the ratio of gold/copper and or other materials used.

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There are very many alloys that are blackish and are historically found in Japan. Tin-rich alloys can be very dark, but the color is permanent - this one is common with Kofun since they naturally retain more tin over long periods. Sulfur alloys (related to modern niello) can be blackish. Finally, shakudo is a huge range of alloys of copper with some gold (usually 1%), silver (usually 1%) and if the piece is late - likely arsenic, that was oxidized by boiling in urushi... There is no guarantee even if top quality shakudo is left in the air that it will result in production of 5-10 nm particles of gold or silver on its surface - and that is exactly what is needed to create the shakudo color. Essentially black is due to overlap of scattering on the surface from very small particles (blueish) with copper oxides' natural absorption spectrum (reddish). "Natural" oxidation will strongly depend on the environment. If your surface particles will end up being larger in size, you will be in a completely different scattering regime (Mie) and the result will be different.

 

Kirill R.

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Good question, I often wonder if there is a way to tell unpatinated shakudo from unpatinated copper. 

Following thread!

 

visually, no, the small addition of gold doesn't alter the copper colour enough to allow our eyes to see any difference. it is possible to tell, however, from the way the metal feels when scraping or polishing. The additions to the copper refine the copper crystal size so that it feels less 'gummy' and slightly more firm.

 

Ancient high tin bronze is sometimes found that is a good glossy black but this wasn't a deliberate finish as far as can be ascertained but rather the result of the conditions the piece was stored or buried in.  Also, these types of bronze are almost always castings and unlikely to be found in tosugu.

 

Niello type alloys are only used as infill decoration and don't appear to have been used in Japan.

 

By the early Meiji period a pseudo shakudo had been developed in Tokyo that contained no gold. The patina on that is a really good solid glossy black. It appears the patina was developed in a kiln and not by the usual boiling in copper salts.

I've not seen this alloy used in tosogu though. And I've never come across any process that boiled metal in urushi though, that sounds alarming dangerous  :-?

 

There is a little chemical test that I sometimes use to test for shakudo or copper on an unpainted piece but I'm not sure making that publicly available would be wise for fear of setting of a flood of DIY screw up repatination attempts.

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Ford et al,

Appreciate the comments. I think one of the hardest things to tell especially with most of us having to rely more on the internet/books for learning is the identification of what type of metals are being used. And as some responses indicate there is a wide range of knowledge on the subject matter. Some responses in this and other forum topics clearly indicate that certain members studied subjects very different than my undergraduate political science major with a minor in film studies. So as I try to progress my studies, I have realized at times simple basic knowledge on base metals is lacking (among other areas). I have been fortunate to have held some pieces but I don't have a consistent way to learn hands on. Obviously, I'm not the only one. I have known since I started that hands on experience is a must. It has amazed me that you can feel quality in some pieces. Afterall, isn't Ford's studies bringing to light things we collectively didn't know or had been forgotten? And since Ford is busy enough and I don't think has time to show up at each of our houses to teach us I appreciate any clues or descriptions that can help me learn. Now I have a target for finding out the "gummy " feeling. Thanks for everyone's input and hope for more as time goes on. All the best

Ken

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This thread is quite old. Please consider starting a new thread rather than reviving this one, unless your post is really relevant and adds to the topic..

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