I have used a hardness tester for about 20 years. While this tool will not identify great pieces of cane, it will help you select out most of the ones that will never be made into good reeds.
For those of you not familiar with a hardness tester (or impact meter), this is how it works and how I use it.
The machine has a pin that is driven into the cane using a consistent amount of force for each test. The result is an extremely small indentation in the gouge of the cane.
The meter measures the pin's depth of penetration into the gouge. The deeper the penetration, the softer the cane.
This method of selection is simple and easy, but there are a few things to keep in mind.
Some Lack of Consistency
Anyone who has used one of these machines knows that no piece of cane yields the same hardness measurement throughout the length of the gouge. Thus, I do a few things to ensure I come up with a measurement that most accurately captures the degree of hardness for the WHOLE piece of gouged cane without spending an inordinate amount of time in measurement.
1. I could share with you the hardness numbers that fall within my "acceptable" range. Unfortunately, the number range I use may be useless to you! Even users of two machines of the same brand may find that the two machines vary in their assessments of hardness for the same piece of cane.
Therefore, some trial and error is necessary in coming up with a number range that is useable.
2. Any piece of cane will vary in hardness throughout its gouge. There are a few ways to even out this inconsistency, though.
Sand the gouge before measuring. Many commercial gouges are rough and uneven. Places on the gouge that are thicker than the rest will yield a higher (softer) measurement than those that are thinner. If the pin drops on a low point in the gouge thickness it may give a reading that is lower (harder) than if it were to fall on a high point.
A light sanding with 400 grade sandpaper will smooth out the peaks and valleys inherent in the grain of the cane and help ensure a more accurate reading.
3. The tip is the most sensitive, reactive part of any reed. Therefore, the most critical part of the gouge for a hardness measurement is in the middle area where the two reed blade tips will be profiled. Since I do not want to place a divot in the gouge in either of these areas, I measure the point exactly midway between the ends of the gouged piece (where the fold will be). This point is close enough to the tip areas to give me an idea of how hard the cane is in these two regions.
4. If the fold measurement doesn't fall within range, I reject those pieces that are too hard. Softer pieces can either be stored for later evaluation -- a year or two of storage is sometimes sufficient for the cane to harden up -- or the cane can be gouged thinner to produce a harder measurement.
5. If the fold measurement falls within the useable range, I will measure the hardness at both ends and average the three numbers to come up with an average hardness for the whole piece. Because some ends have "gouger bites" or other imperfections in the gouge, I always measure in from the end at least a quarter inch.
6. I then write the hardness number on the gouged piece with pencil. Later, I'll write the number on the blade of the finished reed for identification in the reed case.
This method, which takes takes less than a minute for each piece, has saved me a lot of time during the finishing stage as I now work on many fewer questionable blanks. I also worry less that I might be throwing out pieces of cane that I could have used.
You can also use this method for measuring cane that is already shaped. If the cane is profiled as well, simply skip the fold measurement and measure the two ends and average.