Iaido Journal Jan 2005
copyright © 2005 Todd Forbes, all rights reserved
Recently I had the opportunity, and privilege, of repairing my Sensei's
first Iaito. The koiguchi had been well worn in, and there was a
mild crack running down the ha side of the saya. Being the
traditionalist that I am, research was my first step before performing
A traditional saya is made from two boards that have had the inside
carved out to create a very close fit to the blade, without actually
touching the sides of the blade itself. The mouth of the saya, or
koiguchi, is carved and fitted to hold the habaki tightly to prevent
the sword from rattling around in the saya. Unlike European swords,
Japanese swords fit loosely into their saya, and the only part of the
blade that actually touches the inside of the saya is the surface of
the mune. Once the blade is fully inserted into the saya, the
habaki holds it in place with a snug fit with the koiguchi.
-- Repairing the Crack --
My first task was to repair the crack than ran down approximately 2
inches of the saya. This crack did not violate the integrity of
the koiguchi, so I luckily did not have to worry about that one.
It was said that the saya cracked while performing yonhon me tsuka ate,
and I can easily see why. Let that be a word of caution to my
fellow Iaidoka. Traditional saya are constructed so that the
boards can be easily split apart to allow for cleaning and repair of
the saya. I think that is far more than any Iaidoka would want to
do, and I don't think iaito saya's are constructed in the same
manner. To fix the crack, I used Elmer's ProBond. I filled
the crack from the outside and tried my best to get at it from the
inside as well. Once cured, I very carefully smoothened out the
seam with a Stanley knife, to create a uniformed smooth feel. Now
I could focus my attention to repairing the worn koiguchi.
-- Repairing the Koiguchi --
Since the Heian period, saya have been made from the wood of the "Ho"
tree, or Honoki Tree (magnolia). Ho wood was used because it is
soft and won't scratch the blade, and when properly seasoned it has
virtually no sap in it. Ho wood is typically seasoned for about
10 years before it is used for saya construction. Our closest
neighbor to the Ho Tree on this continent is the Yellow Poplar.
Magnolia is both strong and non-resinous, as resins and oils of certain
woods can attack blade steel. With that said, it is a good
guideline to use when choosing a wood to repair a saya with. I
headed down to my local exotic wood store (Black Forest Wood Company),
and picked up a block of Poplar for about $2.50, more wood than I would
It should also be noted that at no time during the saya making process
is any sort of abrasive paper used. The risk is far too great
that if any residual grains of the abrasive material is left behind, it
could seriously scratch the blade. With that said, NO SAND PAPER
OR ABRASIVES DURING REPAIRS!!
- The first step to repairing the koiguchi is to determine how thick of
a shim you need to create. I luckily have a pair of digital
calipers, which I used to measure the inside of the koiguchi, and
compared it to the thickness of the habaki. In my case, I
required approximately a 1.2mm shim. For those who do not have
calipers, just eye ball it.
- Next, I grabbed my largest chisel and chiseled off a piece of poplar
approximately the same size as the habaki in width and length. A
nice sharp Stanley knife will allow you to fine tune the shim so it
fits in the koiguchi.
- Rest the shim against the habaki and insert the iaito into the saya
to test fit the shim. You don't want it too tight, and you don't
want to force the habaki into the koiguchi. The fit should be
snug, not tight. If things are tight, evenly shave off some wood
from the shim with a Stanley knife, and repeat until the fit is nice
Now we need some glue...
Sokui is a Japanese glue made from rice. Japanese carpenters made
this glue by kneading rice with bamboo spatulas. In the old days,
sokui was used as an adhesive for fittings and furniture from the Nara
period in Japan. Sokui was used around the time when people
stopped using hide glue, due to the introduction of Buddhism and the
consequent prohibition of butchering. Sokui is used because it is
strong, but not so strong as to prevent the bond from being broken if
the need arises (eg. saya repair and cleaning).
To make a basic sokui, follow these steps:
- Obtain some 1 or 2 day old rice.
- With a wet bamboo spatula or equivalent, mash rice on a cutting board.
- Add a drop or 2 of water and mash again.
- Keep adding water as needed.
- Continue to mash the rice until it becomes a stick, glutinous mass
with no lumps.
You now have a basic sokui.
Advantages of Using Sokui for Various Repairs:
- No fumes.
- Does not draw moisture.
- Is strong but can be removed for repairs.
- Now that we have some glue, smear a layer of sokui on the shim and
place it nicely inside the koiguchi, I placed mine on the ura
side. Press it firmly against the wall of the saya and remove any
sokui that oozes from the shim.
- From lacking anything better to hold the shim press fit to the inside
of the saya, I returned the iaito to the saya and used the habaki to
hold the shim in place, and snugly against the inside wall of the saya.
- The iaito can be removed the next day, and the sokui should be nice
and dry. Again, carefully with a Stanley knife, I removed any
dried sokui from around the koiguchi.
- With what seems to be my favorite tool, I used my Stanley knife to
shave the shim a little bit to allow for the habaki to slide smoothly
into the saya without catching on the new shim, but maintained the snug
Eventually, the new shim will compress a bit and the fit will not seem
as snug. If it becomes too loose again you can try adding a shim
to the omote side as well, but still be careful not to make it too
tight. Just remember; never force the habaki into the koiguchi,
snug, not tight. If you ever need to reshim your saya, always
remove the old repair. The use of sokui allows for easy removal
of old shims. If you were to use ProBond or any other wood glue,
or other adhesives for that matter, the repair would be more
Overall, I consider the repair successful. One may question the
strength of Sokui, but the bond is amazingly strong. If I were to
say anything to anyone who wished to do repairs on their iaito, I would
recommend they research the operation they wish to perform. More
than just an understanding of what you need to do, but as well as an
understanding as to why you are performing a repair a certain way, and
how it relates historically in a traditional sense.
-Todd Forbes is a member of the
Calgary Muso Shinden Ryu Iaido Club