Sideway Split In Saya

[Valric]

Hi, 

 

I have a shirasaya with a subtle sideway split along the glue line. It came as is, and I presume it was cleaned up by splitting it then re-glued poorly. The horn pieces keep it in one piece but you can still see feint openings. My question is - how bad is it? Presently I've tightened it with leather straps to keep it sealed, but you can't make a perfect seal this way - should I seek repair? If it's not too involved, could I do it myself (rice glue?). I wouldn't want moisture to get down in there and make a mess. 

 

Thank for the advice, 

 

Chris 

[pcfarrar]

A few dabs of warm water and then clamp it shut. The hot water should reactivate the rice glue and it will seal again.

[Katsujinken]

Worst case you can wrap some *acid free* tape around the area.

[Brando]

You can make a diluted mixture of 50% wood glue, 50% water......use a thumb tack to keep the split open as you carefully wipe a sponge with the mixture across the split. pull thumb tack out,..put a spring loaded clamp on from the opposite side of the split and clean any excess glue with a damp paper towel before it drys.  You can also use a folded up dry paper towel between the clamp and saya while clamping to avoid any clamp damage to the saya finish....it will be dry in less than an hour.

[SAS]

Some kinds of "wood glue" will accelerate rusting....ask me how i know....  rice glue  was used and still is for good reason. I would avoid anything that would change the external finished surface, like wood glue.

[Valric]

Thank you. Rice glue is surprisingly easy to make from what I've gathered and it's probably the safest (wood glue would surely hold up better). I'll make a batch and apply it to the split area. With the moisture it should as well reactivate the existing glue. I don't have a regular saya for the blade so I'll just keep it well oiled in a dry place as it will take time to dry.

[Grey Doffin]

To clamp the saya while the glue sets (you don't have to use clamps if you don't use glue) try this.  Cuts strips of white paper about an inch across and long enough to go 1 1/2 times around the saya.  Wrap a strip around the saya about 6 or so inches below where you want the clamp and then tightly wrap the paper with masking tape...Place the saya mouth-down on a table and force the tape/paper strip downward.  Since the saya is largest diameter at the mouth, as the tape/paper is shoved down it will tighten.  Reverse the shove to remove.  Be sure to prepare the strips before applying glue; you want to move quickly once the glue is on.

This is a great temporary fix for a splitting saya.  The strips exert lots of force in just the right places and since no tape touches the saya they are reversible and leave no trace.

Grey

[obiwanknabbe]

on my own work (swords and knives that I have forged) i have had success with binary epoxy. Its humid as all heck down here and i have not had any rusting issues. I have used it in conjunction with 1095, 1080, 1070, 80crv and W1.. no rust. Rice glue best if you have it.. 

 

Kurt K

[nagamaki - Franco]

FYI, bought a tube of this glue (linked) along with a roll of rice paper for oshigata, but have not tried either yet.

 

https://www.amazon.com/Yamato-Nori-Rice-Sticking-Paste/dp/B002L9YLHQ/ref=sr_1_1?ie=UTF8&qid=1503557703&sr=8-1&keywords=Yamato+Nori+Rice+Sticking+Paste-+220g+Tube

[Dr Fox]

A sleeping case for a sword blade, is meant to be separated to allow cleaning, and refitting for its blade after a polish.

For this reason alone, never use any adhesive that will give a permanant fix.

Rice glue is used for the very reason, that with warm water the saya can be separated.

To need your saya separated, only to find someone has previously 'glued' it will mean sawing it apart.

I know I have been there. Don't do it its bad form.

[Valric]

Indeed Denis. I think in fact someone cleaned that very sayagaki recently. The sword has a few uchiko gung-ball scratches, so there you have it. 

 

Grey, that's a very good tip. I'll do exactly that. 

[Dave R]

 I make my own rice glue, which is not very difficult at all. I would suggest using a "sticky rice" as is sold for sushi..... I don't know how well another rice such as basmati would work, and for what it costs why use any other.

[Darcy]

Shirasaya splitting along the seam is a feature. It's not a problem. 

 

When you glue wood you have a choice of what you want to be stronger: the wood, or the glue. Modern glue is a lot stronger than wood so once it binds you get a lot of stress that builds up in the wood as humidity makes it change its shape. The resulting force usually gets released at some point by ripping the wood. 

 

I once made a square frame of wenge and used a bunch of end-grain-up inside that was scrap wood and made a nice butcher block table. I wasn't aware of the problem of wood moving with humidity. I made this in summer. The bonding surfaces on this wood were about 3 inches x 2 inches usually. When the stress released it was like lightning struck inside my house. It ripped in half the wood blocks all through the center of the tabletop. So imagine taking a block of wood, 3 inches high, 3 inches long, 2 inches wide and just pulling on either side until it rips. This is pressure that the wood exerts on itself due to humidity changes.

 

So when you put wood glue in a shirasaya you are playing the same game. If humidity moves the shirasaya you will rip the wood and kill the shirasaya and the release of energy is maybe going to damage the sword.

 

Rice glue being weaker than wood, the rice glue will gracefully fail before any problems occur. In which case you finish splitting the shirasaya, take the opportunity to clean the inside, and then you simply reglue it. It is better to just finish the splitting of it and redo the whole thing than to patch it, because half of it is probably still under some stress, just not the level to make it fail yet. You need to test carefully for fit before gluing. 

 

Anyway just wanted to insert why you want to keep wood glue far away from your shirasaya.

[Geraint]

Nothing that I am about to say will change the very sound advice to use only rice glue for shirasaya..  With respect large end grain chunks of Wenge splitting is a rather different case to the timber movement in a shirasaya.  Wood as an organic material will absorb and give up moisture throughout it's life and in doing so will change size and shape however it is the way in which the changes occur that is interesting.  Green or newly felled timber will lose a great deal of moisture as it seasons and sections of timber will change shape.  The wood will shrink as it loses moisture but crucially it will shrink more radially, ie in line with the annual rings if they are present, than it does tangentially, ie in line with the rays if they are visible.

This diagram illustrates what happens.

 

 

If we look at the upper left then the problem of end grain squares becomes obvious, they are going to change shape and nothing you can do will stop them as they adjust either to a dry environment in a centrally heated house for example or if they are exposed to direct sunlight, or indeed if they are in a higher humidity environment.

 

Lower left is the situation that should apply to shirasaya, what woodworkers call quarter sawn timber.  Given the orientation of the growth rings, and the same applies to species where these are not evident, the timber will change size but not shape.  Now if your shirasaya craftsman knows his stuff he will have taken a well seasoned piece of quarter sawn timber and having cut the profile of the shirasaya, the curve of the sword, he will split the timber into two, carve the inside of the saya and eventually glue the two halves together in the same orientation.  The upshot of all this skill is that the grain direction in both pieces is running the same way and in effect the two pieces have been reunited.  The consequence is that when the timber moves, and it will unless kept in exactly the same humidity and conditions that it was made in, then the two halves will move as one.  Unless the piece is particularly rouge there should not be any warping or twisting but the overall size will change slightly, hence the common question about habaki sticking.  

 

The difference in movement is about twice as much radially as it is tangentially, which is why quarter sawn timber is sought after, but the change in length is almost negligible.  Shrinkage or expansion across the grain can be as much as 1mm in 33mm, doesn't sound much I know but as Darcy says it will rip your furniture apart if you don,t design for it.

 

Please forgive an ardent woodworker for this elaborate response.

 

All the best.

[Darcy]

With respect large end grain chunks of Wenge splitting is a rather different case to the timber movement in a shirasaya.

 

The anecdote is primarily to illustrate why you want to use rice glue and not wood glue.

 

For the rest:

 

1. swords are not straight

2. it is getting harder to find ideal blocks of wood for shirasaya

3. the shirasaya goes on a metal object, which means you have a living size changing object and a relatively stable object and they are expected to maintain half-millimeter tolerances in all weather conditions, and it cannot be made to be perfect in this situation

 

Back to the end grain analysis, take the tsuka off the shirasaya and look down the tsuka and ask me what is facing your noggin (end grain). That end grain is going to shrink and expand like the chunks of wood in my anecdote. The interior space is going to open up and it is going to close down.

 

When this happens at the mouth of the shirasaya and the habaki is in place there tightly, this acts as a wedge and splits the shirasaya down from this point. 

 

When this happens, you pick your poison: the glue breaks or the wood breaks.

 

As for the rest, I know the theory and I built a lot of things from wood. Humidity can make it so loose that a sword with habaki on it will fall right out and the tsuka will fall off. Humidity can make it so that the tsuka cannot be removed and that the sword will not fit in the shirasaya anymore, even discounting the habaki. All of this implies large amounts of shape change.

 

I split my thumb to the bone on a Yosozaemon Sukesada that was stuck fast in the shirasaya by this compression force. I should have backed off but I applied a lot of muscle and when the thing broke free I ended up hitting the edge of the blade with my thumb. Didn't feel a thing. Didn't know for sure I was cut until I flexed the thumb and the flesh parted like the red sea.

 

In Montreal in the winter, a lot of my swords would go only to about half the depth of the habaki and be in tight. These were Juyo and Tokubetsu Juyo and not junk wood involved. After the Yosozaemon I was very careful about how I set them up as winter came. 

 

When they arrived from Japan they fit just fine and no binding at all. Everything made to spec.

 

After winter, swords often came out along with sawdust.

 

So, theory is nice, but when it butts up against reality the theory needs a bit of tweaking.

 

With all wood, whenever you move it from where it's built, to where it's going to be, if you have large humidity and temperature swings you are going to get wood movement. If the thing was designed to allow movement, you won't get failure. If it was not designed to allow movement, you get failure. 

 

Shirasaya are not a technology that was meant to be employed far away from its place of creation. They were not designed with wood movement in mind. For the most part the sword deals with being put in tension and compression by the shirasaya and because it is what it is, the situation manages itself until it goes to an extreme. When it hits the extreme, the shirasaya fails, and as mentioned, choose the glue or the wood at that point. 

 

Take your average well made shirasaya and have it sit empty and it should mostly be fine. The stresses the wood is under are below the failure point of the glue and the wood. Put the sword in and you have a different situation. Have a non-ideal piece of wood and you have another variable.