Best way to keep humidity away from tsuka

[jeremy]

Hi guys,

 

Hope all you people are doing well. I haven't posted here for a long time, so its good to be back!

 

What I wanted to ask is what is the best way to protect tsuka from humidity? The sword I use for iaido has nicely made Japanese honoki tsuka and have found that it expands when there is excess moisture in the air, which allows the nakago to rattle a little inside the tsuka core. When the humidity drops I have noticed it shrinks back and the rattle disappears. But the problem is that when i have to train when the tsuka is rattling. I know i can wait until it dries out, but because the humidity here is so often high, I cant always wait until it dries out. So, whats the best way to keep away moisture from swords? I have built a wooden box for it, and place it under my bed along with dehumidifiers inside, but it seems that they dont work too well. Anything else out there?

 

Thanks in advance,

 

Jeremy Hagop

[David Flynn]

Moisture absorbing crystals. Buy in Bulk from hardware store.

[Veli]

Hi!

 

The amount of water absorbed by wood depends on the RH (Relative Humidity) of air. RH can be lowered either by removing water from air (by salt crystals etc), or simply by increasing the temperature. The temperature under your bed is probably lower than elsewhere in your apartment (unless you have floor heating), and thus the RH is higher in there. Try to move the sword to a warmer location (remember that warm air rises upwards). If you have 75% RH at 23 deg C , and you lower the temperature to 20 deg C, the RH rises to 90%, which means big problems (mold etc). Small temperature change makes a big difference!

 

Remember that if you use moisture absorbers, they need to be regenerated regularly!

 

To those who wish to dive deeper into secrets of moisture calculations:

http://www.vaisala.com/humiditycalculator.html

 

BR, Veli

[John A Stuart]

You don't want a koshirae in an arrid atmosphere. The saya will crack the same become brittle. So driers when too humid and humidifiers when too dry. Keeping your sword enclosed prevents radical changes in humidity. You can keep an eye on humidity and adjust accordingly with an hygrometer. For $12 a terrarium model will work. John

[jeremy]

Thanks for the replies gentlemen. I just purchased a de-humidifier for my room which keeps the room at a set RH of 60% which in my experience is a safe humidity level for both the sword and I!

 

Kind regards,

 

Jeremy Hagop

[Ford Hallam]

I think perhaps you're seeing things back to front, Jeremy. :D

 

When wood dries out it shrinks....but it shrinks in on itself. It may help to think of the tsuka as two slabs of wood, each shrinking in on themselves. What this means is a dried out tsuka will have an opening for the nakago that is now effectively bigger, hence the looseness. If, on the other hand, the wood absorbs moisture from the air then it will swell...again in all directions, and tightening the grip on the nakago.

 

So really, to ensure a tight fit you should ensure the tsuka doesn't dry out too much.

[nagamaki - Franco]

What this means is a dried out tsuka will have an opening for the nakago that is now effectively bigger, hence the looseness. If, on the other hand, the wood absorbs moisture from the air then it will swell...again in all directions, and tightening the grip on the nakago.

 

So really, to ensure a tight fit you should ensure the tsuka doesn't dry out too much.

 

Hi Ford,

 

If I'm reading and understanding your statement correctly, please explain why it is during the winter months when the air is relatively dry in the NE U.S., that the shirasaya including the tsuka tighten up so much on the nakago and habaki that if not pre-loosened come November, it will be spring time before you're able to remove them again? And, come spring when the humidity rises again, no problems, the shirasaya including the tsuka fit perfect once again on the nakago and habaki? Thanks.

[Veli]

Gentlemen,

 

I guess it can be either way, though usually shirasaya and tsuka do tend to tighten during the cold and dry season. Wood is an anisotropic material: If fresh-cut wood is dried to near zero percent moisture, it shrinks 0.1-0.3% lengthwise, 3-6% radially and 6-12% tangentially. Thus, depending on the construction and grain direction, different (geometrical) forms of shrinkage can take place.

 

BR, Veli

[Nobody]

My doughnut theory does not take account of its anisotropy. But still it will explain that the hole will be tightened when wood is dry and shrinks, and the hole will be loosened when wood becomes moist.

Ref. viewtopic.php?f=1&t=1724&p=11749&hilit=doughnut#p11749

[Ford Hallam]

Franco,

 

I was taking my point of reference from comments by Kazuyuki Takayama (mukansa shirasaya-shi) Page 149, The Craft of the Japanese Sword.

 

"For a blade that is going to a drier climate than humid Tokyo's, for example, the fit of the scabbard must be very loose, almost to the point that the blade falls out by itself. Once the scabbard reaches it's destination, the much lower humidity will cause the wood to shrink, resulting in a perfect fit."

 

In my experience this means that a tsuka that has lost a significant amount of the moisture that was present when it was made ( and presumably perfectly tight fitting) often has an opening that is less tight. Of course, I was addressing Jeremy's question in relation to a wrapped handle. On a shirasaya the wood is nearly 3 times thicker so I suppose the physical movement of the wood may be quite different and as Veli points out, the orientation of the wood grain plays a major part in how the tsuka and saya will react. Maybe your shirasaya maker didn't compensate enough

 

I remember, as a devout young alter boy, being amazed at a collection of tiny wooden replicas of the tools, a ladder and the cross supposedly used in the crucifixion, all crafted so that they could be assembled inside a bottle which was then filled with holy water. The resultant swelling of the wood served to secure all the tiny joints. But perhaps that only works with holy water ...so Jeremy might try getting his sword sprinkled with holy water and blessed while he's at it :D

 

regards,

 

Ford

[nagamaki - Franco]

Hi Ford,

 

No worries, I'm just trying to be difficult in this case . The idea of opposite effects with seasonal changes here in the NE often catches the shirasaya makers off guard, too. After having shirasaya made both on the loose and tight side, my preference is on the tight side for safety and storage reasons. It requires a bit more awareness when seasonal changes arrive, but that goes hand in hand with sword care anyway.

[Jean]

Good examples :

 

In Paris, We are stiil in winter and overheated in my flat ( nine floors and I live on the third one). Atmosphere is very dry even with bowls filled with water

 

The mouth of my T... shirasaya has shrinken so much so that I can only enter half of the habaki.

 

I cannot remove either the shirasaya tsuka of my K... tanto.

[John A Stuart]

Very bad for all wooden products, especially fine furniture, Jean. A good investment would be a small humidifier for the dry months. A good indication that it is too dry is when every thing touched, that has metal, creates static discharge. Part of my weather recording equipment in the house is an hygrometer that can be used to monitor relative humidity. A neccessity when using an humidifier since too moist of an environment promotes mildew and other molds. I believe corks in wine bottles like it humid, they don't break on opening and also won't let the wine spoil as easily from a bad cork. John

[Jean]

You are entirely right concerning the furniture John (as well as lacquer work) it is at the time being my main concern.

 

In fact I need at least four humidifiers, one for each room. I would like them small and the less cumbersome.