Gold paint inside saya?

[Jorgensen]

-I have an old saya that is split (for a Daido Naginata Naoshi blade) and discovered it is goldpainted inside... Have any of you ever experienced a saya was goldpainted inside it and any idea of what is the purpose of this?

 

- Jorgensen

[Jorgensen]

Update with pictures...

[Grey Doffin]

Hi Jorgensen,

Might this be gold leaf, put there to stop the transmission of water vapor?

Grey

[NihontoEurope]

Grey,

 

Having gold in contact with lower quality metal would cause the low quality metal to oxidise if there is moist. Moist will inevitably surround the blade in the saya. It would be an oxidised battery effect in the end, where the low end metal will take penalty agains high end metal.

 

The effect wished for could have been what you say.

 

This is my thoughts. I might be wrong and you right.

 

/Martin

[hxv]

Hi Martin,

 

You are describing correctly a common effect occurring when two different metals come into contact with each other. A thermal-couple voltage arises at the junction (contact point). This thermal-couple voltage varies with the temperature of the junction. In fact, that's exactly how thermal-couple probes work to measure temperatures. The temperature versus voltage curve is tabulated and calibrated (experimentally) for each type of junction. We stick that thermal couple junction into the location where we wish to measure the temperature and read off the voltage that results at the junction. The tabulated (calibration) data will tell us what the temperature is from the voltage.

 

By the same token, we don't want to join copper tubing with galvanized tubing in our household plumbing lines as the resulting thermal-couple voltage at the junction of two different metals will cause the junction to corrode with time.

 

However, it means that having gold come in contact with another metal (the nihonto in this case) will be detrimental to the nihonto as the thermal couple voltage will cause the nihonto to corrode over time. Gold doesn't care as it is an inert metal. The nihonto cares, though.

 

The effect is the opposite of what we hope for. There must be different reason for the gold paint. I am not smart enough to figure that one out, though

 

Regards,

Hoanh

[Grey Doffin]

Not questioning the information, but curious. Why then can an iron tsuba have gold inlaid and not corrode over centuries of contact?

Grey

[hxv]

Hi Grey,

 

You have the mind of a scientist, always one step ahead The magnitude of the thermo-couple voltage depends on three factors: type of junction, temperature of the junction, and the lengths of the lead wires on either side of the junction. In the case of a tsuba gold inlay, the amount of material is not enough the generate a sufficiently large thermo-couple voltage to cause corrosion. In the case of plumbing pipping, if there is material mismatch (copper+galvanized pipes), usually the pipe lengths are fairly significant that corrosion will eventually occur, over periods of decades. You, sir, have a very sharp and logical mind. I appreciate it!

 

Regards,

Hoanh

[NihontoEurope]

Not questioning the information, but curious. Why then can an iron tsuba have gold inlaid and not corrode over centuries of contact?

Grey

 

Grey,

 

Many tsubas have a fine patinated surface that protects this from happening. It is all about the mixture of metal. The smiths back in those days where very intelligent, but they had no academic idea of why things happened. This is why we can see tsubas today that shine very brightly and appears to be new although they are a couple of centuries old, whereas a newer one has totally deteriorated in some areas.

 

I have a couple of tsubas, made from a poor smith, that have this effect shown. The erosion/oxidation is around the high-end metal. Two things have caused this:

1. poorly made tsuba

2. poorly care of the tsuba

 

If a tsuba has a well done patinated surface and treated during the lifecycle to allow a natural patina this battery effect will not occur even if subjected to moisture. Today collectors apply skin fat from their own body to further patinise the tsubas.

 

Basically - Rust is rust preventive (in the right state). An eye for an eye...

 

One can spend an eternity on metallurgy. The Japanese started a long time ago. If they knew what we know today; how would the swords look like?

 

Perhaps the gold inlay is to honour the sword as it was resting in the saya. The samurai souls rested there.

 

/Martin

[hxv]

Hi Martin,

 

Very well put and poetic. I like your explanation and the way you put it.

 

Regards,

Hoanh

[Ken-Hawaii]

Hoanh, gold will not cause anything to corrode. Galvanic action only occurs when there is a different electrical potential between/among metals. Take a quick look at http://www.engineersedge.com/galvanic_capatability.htm, & you will see that gold's anodic index is zero, which means there just isn't any dissimilarity between it & iron. They will happily coexist forever.

 

I'm not sure why the saya would be lined with gold leaf, at least from an engineer's standpoint....

 

Ken

[Ted Tenold]

This may have been an effort to seal the grain so that oil would not saturate the wood fiber, or perhaps an effort to keep grit and contaminates from collecting too. I think it can be catagorized as an interesting addition with little applicable practicality. Also not enough gold wieght in the leaf to be appreciable "portable wealth".

[runagmc]

Hoanh, gold will not cause anything to corrode. Galvanic action only occurs when there is a different electrical potential between/among metals. Take a quick look at http://www.engineersedge.com/galvanic_capatability.htm, & you will see that gold's anodic index is zero, which means there just isn't any dissimilarity between it & iron. They will happily coexist forever.

 

I'm not sure why the saya would be lined with gold leaf, at least from an engineer's standpoint....

 

Ken

Ken, Hoanh is right. I tried to look at the page you linked to, but it didn't show up.

 

Galvanic reaction occurs when two metals with potential difference are electrically connected in in the presence of an electrolyte. Gold is at the top of the anodic index at 0 because it is the most cathodic of all the metals, while iron is more anodic with an anodic index of -0.85. That means iron has a strong potential difference from gold and will corrode if electrically connected and in the presence of an electrolyte. http://en.wikipedia.org/wiki/Galvanic_series

http://en.wikipedia.org/wiki/Galvanic_corrosion

 

Gold will not corrode as part of a galvanic couple (as far as I know), but it will cause pretty much all other metals to corrode if they are in the presence of an electrolyte... so the rate of corrosion will depend on the environment.

 

At least, this is my understanding.

[runagmc]

Also, it should be mentioned that the same kind of corrosion occurs under and around habaki, with moisture (aka water - the more salty, the more electrolytic) acting as the electrolyte.

[hxv]

Gentlemen,

 

Let me confess up front in the spirit of full disclosure! I am a physicist, not an engineer and far from a chemist, but here goes. What Adam said is exactly right. From a chemist's point of view, the electromotive potential for Au+ +e- = Au is 1.692V, and the electromotive potential for Fe++ + 2e- = Fe id -0.447V. The net electromotive potential for the Au/Fe junction, in the presence of an aqueous solution is 2*1.692V-(-0.447V)=3.831V. Because Au is an inert metal, the corrosion will occur only on the Fe side. Adam is also correct in saying that the same galvanic reaction occurs under the habaki. My numbers may not be precisely correct, but they are in the right ballpark. After all, I'm a physicist. If I'm within a factor of 2 from the correct answer, I'm happy.

 

Regards,

Hoanh

[Jorgensen]

Wow, this gets really scientific... Wonder if this would be a job for Mythbusters on Discovery

 

However, my friend and fellow collector came up with this teori, that the gold could be added inside saya to preserve a new polished blade, instead of "cleaning" saya or make new saya/shira-saya? Very close to Ted's theory.

 

But if gold corrodes metal, its a bit like shooting yourself in the foot! =) Unless if the sword was often used and cleaned at that time, it would'nt manage to corrode?

[hxv]

Hi J. Jorgensen,

 

If the sword is taken out and cleaned often, then I don't see a problem.

 

Regards,

Hoanh

[Surfson]

The principle of a thermocouple is best appreciated if you chew aluminum foil. Anybody who has fillings can't do this since the generated electricity goes right to the nerves of the tooth (teeth are very well innervated which is why torturers sometimes use them while practicing their art). If you have no filings, you can chew aluminum foil with impunity and simultaneously make everybody in the area cringe.

[Peter Bleed]

Gee Gang,

The list has been on fire recently and this has been a fun thread.

I will only add to the discussion that a galvanic response requires three things: an anode, a diode, AND an electrolyte, you need need a plus, a minus, and something to carry a current. Water will do it, but air ain't so good and neither is choji. So an oiled or dry blade shouldn't enter into active galvanic activity - especially it the habaki is doing its job.

The main thing that this thread is demonstrating is that WE probably to know more about galvanic responses than did Edo period sword workers!

Peter

[runagmc]

Peter, I agree with everthing, except that instead of diode, I think you mean cathode. A diode is a solid state electrical device made from two semiconductors (usually silicon) with the basic function of acting like a check valve in an electrical circuit (meaning it allows current flow in one direction only). There many types of diodes with many potential uses. Sometimes the two leads of a diode are also called the anode and cathode...