To get a general appreciation for the inner life of bamboo let’s do some experiments which might be suitable for the junior high science fair. Bamboo has openings (tubes) in its structure which run the entire length which the plant uses to transport water/sap. For the most part, sap is sugar water and the sugar is, for the most part, glucose (C6 H12 O6). As a point of interest, cellulose is glucose minus one water molecule (C6 H10 O5).

First Experiment: Demonstrate the tubes

Cut a couple pieces of bamboo 2” long.
Put 1/2” of water in one paper cup and 1/2” of alcohol in another.
Place bamboo sections in each cup.

Watch carefully, as the alcohol will make it to the top in a few seconds. The water will take minutes if at all. Why? Water is more viscous than alcohol, but more importantly, the albumen in the cells hydrate and swell, closing the tubes. Albumen is the clear stuff in eggs. And it can be hardened by heat, as in frying an egg. Albumen is present in almost all biological cells including bamboo. It is kind of a gel when hydrated (think egg again) and shrinks when dry. For a dramatic demstration put a little food coloring in the alcohol so you can really see how long it takes for it to reach the top of your sample. I've seen it rise so fast that it sprays tiny droplets when it gets to the top. The dye will give you a good idea of the distribution of the tubes.

Leave both samples in their cups for 30-60 minutes, then remove and examine the bottoms. The water sample swelled, the alcohol didn’t. The water sample started to soak in the ‘bark’ layer, the alcohol didn’t—and never will no matter how long you leave it. The top of the alcohol sample wetted almost immediately and the water sample didn’t and probably didn’t even after an hour.

Second Experiment: Evaluate water/alcohol as filling agents

Cut a couple sections of bamboo 1/2” long. With an exacto knife or chisel, split one side of the bamboo. The sample should spring open, leaving a gap in the bamboo. The size of the gap tells you the degree of stress the bamboo was under just before you split it. So, one can saw a small sample off the end of a culm, split it and have an immediate and excellent indication of the stress the culm is experiencing, thus the crackability of the culm.

Put 3/4” of water in one paper cup and 3/4” of alcohol in another.
Place bamboo sections in each cup.

For bonus points, notice what percentage of the bamboo is below the water’s surface when you first place it in the cup. This percentage is the bamboo’s specific gravity. The specific gravity of maple is 0.54, oak 0.66, walnut 0.55, hickory 0.74. Getting the picture? Contrary to ordinary intuition, bamboo is a very dense material compared to woods. Place the sample in the upright position to get a good reading.

By watching the gaps of our samples we have very good, real time indicators of what’s going on in the wood. The gap of the water sample will expand slightly for maybe 30-60 minutes and then begin to close. In a few hours it’ll be closed. What this tells us is that the inner part of bamboo takes up water a little faster than the outer. The gap in the alcohol sample will do very little and the gap won’t close. Should you want you can repeat this gap experiment with different solutions (acetone, mineral spirits, oil, etc.) they’ll be about the same as alcohol. The conclusion is that water is filling cells that other fluids don’t and that as long as a gap remains the potential for cracking remains. Now take the samples out of their solutions and watch the gaps during their drying cycles. This single experiment conveys a tremendous amount of information about cracking in general, the potential of any particular piece of bamboo to crack during service and the cellular structure of bamboo.

Let's really understand the stresses in your flute. Cut some 1/2" sections again. Slowly and carefully make the splitting cut on the inside of the rim. Notice how deep and how much effort you have to expend to get the bamboo to spring open. Now do the same thing to the outer edge of the rim. Notice a distinct difference? The inner part of your samples are under compression and the outer part is experiencing tension. When freed, these two forces create the gap. With highly stressed samples (big gap) it is scary to see that a slight touch to the outer rim can split the thing while the inner rim take considerably more force. Keep cutting and splitting samples until you really get it that if you bandsawed a sample out of the middle of your bamboo flute right now it'd pop open about the same way.

What’s needed is some treatment of bamboo where the gap closes and remains closed. If that's ever achieved through the miracle of modern chemistry, the bamboo will have no (zero, nada) propensity to crack.

This gap method is very instructive, but further, it can serve as an aid in making shaks. If one were to cut a small sample from the top of the culm and did the same (any treatments, lacquer, humid box, oiling, etc.) to it as the culm, one would have a real time indicator of the stresses in the flute. That the gap sample came from the culm would guarantee identical bamboo morphologies—thus identical responses to treatments, moisture, etc.

Forget the moisture meter! Keeping a small section of split bamboo with your flute will provide instant feedback about moisture conditions. Just keep an eye on the width of the gap because it tells you what you really want to know--the amount of stress your flute is experiencing. And until the flute is hydrated back to the condition of a living plant it's experiencing some degree of stress!

Let's be clear about this. There's a myth that 'seasoning' somehow reduces stress. Actually, there are two myths. 1) That 'seasoning' is somehow different than drying. Wrong. There are no structural changes in wood as it drys other than the loss of water. 2) That if bamboo is 'seasoned' for 2 or 3 years the stress is gone. Wrong again. If you really want to test this then cut a small section from a 'seasoned' culm and perform a simple gap test. Takes 30 seconds.

Until a suitable bamboo treatment appears, there's a way to make virtually crack resistant flutes. They should be free enough from cracking that you could guarentee them as such.

I was at eBay looking at the shaks and noticed a strange 1.8. And I get to looking at it and thinking that maybe the piece of bamboo would be worth something. I put in a low bid and won the thing. It arrives a week later from Japan and was a monster, weighing in at 410 grams. We're talkin' club--thick heavy walls. Badly out of tune. Within 12 hours it starts to snap--those ominous cracking sounds. In less than 24 hours long cracks are developing on the front, through the holes, etc. It had a crack on the upper back from the fifth hole to the chin-rest which had been bound in five places--nice rattan work. This crack was now heading for the foot at a rate of about an inch an hour. Decision time. Do I want to devote the rest of my life attending to the moisture needs of this stupid piece of bamboo? Since I'd been experimenting with splitting bamboo into two pieces and gluing them back together, it was time to test the theories--time for Bamboo Stress Relief.

Here's the theory: If bamboo is split into two parts, thereby relieving all internal stress, and glued back together it should be substantially stress free for the rest of eturnity. This seemed to work pretty well as I could split, glue, soak in water for a couple days and then oven dry and the pieces held together with no cracks.

I decided to spit the sucker sidewise before the cracks on front and back got badly out of control. It was time for the chisel and the big hammer. Starting at the foot I got the split going, cut all the bindings off and finally got the thing freed into two pieces. The cracks on the front closed up once the strain was released. The historic crack on the back stayed about the same. Strange brown lacquered putty stuff in the bore broke up during the splitting.

So, I let it acclimate to the dry climate in Northern New Mexico, glued it back together with epoxy, reaming it out a little more and then sent it off to Monty Levenson for a poured bore.

If you try this stress reduction method, really dry the split pieces before gluing them back together. Get the moisture content down so that for the rest of it's life the flute will naturally experience higher moisture conditions--even in dry climates. What we've done by splitting, drying and gluing is to reverse the stresses. The outer wall of the flute will now be in compression and the inner wall in tension. If there ever is a crack it'll be on the inside--strange, but true. I've run glued samples through serveral cycles of total water saturation, then oven drying to no ill effects. From the rain forrest to the Sahara and back again. The nice thing about this method of stress relief is that if the flute ever really dried out it'd be back to the state at which you glued it--zero stress. Every degree in the rise of moisture level in the flute just compresses the outer surface and makes it harder.