Mujitsu and Tairaku's Shakuhachi BBQ

dstone · 2006-07-19 11:31:47

I'm continuing a thread here to keep my un-pro musings out of the "ask a pro" forum...

Edosan wrote:
I contend that, due to its nature, the inner surface of the bamboo is more subject to moisture gain/loss than the outer surface, thus the point that jiari shakuhachi lose less moisture, or at least lose it at a slower rate.

ANY shakuhachi is likely to crack if allowed to dry out and lose moisture long enough, it'll just take a bit more time for those with filled bores.

Sure, that makes sense, Ed. Thinking out loud here... (please jump on my mistakes...)

C = Ci + Co + Ce + Ch (total moisture change = change inside + change outside + change thru ends + change thru hole sides)

Those are all the interfaces of the bamboo to the atmosphere.

So...
|JiariCi| << |JinashiCi| (sealed bore)
JiariCo = JinashiCo (unless lacquered/sealed outside)
|JiariCe| <= |JinashiCe| (depends if sealed on ends)
|JiariCh| <= |JinashiCh| (hole sides typically sealed, with bore)
Thus, overall |JiariC| < |JinashiC|, as you say.

Observing that...
1) Cracks develop as a wedge, from the outside in.
2) You can close up a crack by adding moisture to the outside surface (damp towel), showing that the skin will definitely accept and give up moisture. (Jiari and jinashi being equal this way.)

So it seems to me the conditions for most cracks are not simply when C is negative (when the whole flute dries out), but when Co is much more negative (proportionally) than Ci (when the outer surface dries faster than the inner surface).

This is why I don't yet understand why a jiari flute would be less likely to crack than a jinashi. Sealed and unsealed bores seem equally likely to have their outside surfaces dry more quickly than their inside -- the precondition for a crack.

Thanks for bearing with me thru that. I will yield to the more experienced now...

-Darren.

Teaman · 2006-07-19 22:53:06

A couple of points if I may-

A crack dosen't always happen from the outside in. The outside of the flute just has the most exposure to the environment, hence the vapor is released faster; creating an imbalance between the outside and the inside, forcing the bamboo to move (and possibly rip itself apart) in order to deal with the opposing stresses. It is a very likely way for a crack to happen, but is not a rule.

Remember that finishing the inside of the bore is more for sound adjustment than for moisture control. Putting finish on something dosen't mean that it will be protected from vapor exchange. There are many factors, such as the type of finish, how well it is applied, how much of it, etc..

When you add moisture to "close a crack" you are not really closing the crack. All you are doing is swelling the surrounding fibers, but the damage is done. Once the moisture goes, the fibers no longer have a reason to be swollen, and the bond between the fibers was destroyed by the crack.

I really have no data in order to compare the jiari and jinashi flutes in terms of vapor resistance, but I know that there are many other factors involved, the above being just a couple of them.

dstone · 2006-07-19 23:53:04

Teaman wrote:
When you add moisture to "close a crack" you are not really closing the crack. All you are doing is swelling the surrounding fibers, but the damage is done. Once the moisture goes, the fibers no longer have a reason to be swollen, and the bond between the fibers was destroyed by the crack.

Yes, sorry I wasn't clear... I only meant to illustrate that a flute can both lose and absorb moisture quickly through its outside circumference and skin to dramatic effect. Not as a repair for a crack, but to show that a sealed bore won't prevent big changes in the outer surface, where, as you say, the flute has the most (thus, uneven) exposure to being dried.

-Darren.

pablo63 · 2006-09-18 15:09:48

I am not a flute maker but I do have an interest in all aspects of shakuahchi. Would a lacquer or varnish protect the bamboo from damage due to moisture? If so, what type would one use? I live in Northwest Washington so there is no true concern about it getting too little moisture. If I left it alone it would probably grow a few inches a day!

Tairaku 太楽 · 2006-09-18 15:49:18

dstone wrote:
I

This is why I don't yet understand why a jiari flute would be less likely to crack than a jinashi. Sealed and unsealed bores seem equally likely to have their outside surfaces dry more quickly than their inside -- the precondition for a crack.

Thanks for bearing with me thru that. I will yield to the more experienced now...

-Darren.

My experience has been that to the contrary jiari flutes are more likely to crack than jinashi. And my theory is that this is because the urushi and the bamboo expand and contract at different rates therefore putting stress on the flute. I can't prove either thing however.

Mujitsu and Tairaku's Shakuhachi BBQ

#1 2006-07-19 11:31:47

Why flutes crack

Edosan wrote:

#2 2006-07-19 22:53:06

Re: Why flutes crack

#3 2006-07-19 23:53:04

Re: Why flutes crack

Teaman wrote:

#4 2006-09-18 15:09:48

Re: Why flutes crack

#5 2006-09-18 15:49:18

Re: Why flutes crack

dstone wrote:

Board footer