While heat treating bamboo is almost universally accepted as necessary to properly temper bamboo in making fly rods, the temperature, duration, and heating method differ widely. Until recently, I had only been able to find articles on the subject based on various makers’ personal experiences and preferences, generally arrived at through trial and error.
However, Bamboo in the Laboratory (an excellent article by Dr. Wolfram Schott) can be found In Power Fibers Online and viewed at Power Fibers’ download site at http://www.powerfibers.com/html/downloads.html. This article provides a scientific approach to heat treating.
For my purposes, Dr. Schott’s data leads me to the following:
- Over time, Bamboo tends to regain most of the moisture driven out of it during heat treating. Rapid gains take place during the first month following treatment and slow gains continue through the next 9 months (10 months being the duration of the data). It appears that the heat treated Bamboo stabilizes at approximately 1% weight loss relative to weight prior to heat treatment. See Figure 8 page 11 of Bamboo in the Laboratory and associated findings. Note that varnish (any sealant) is no permanent barrier to reabsorbing moisture (although some retard the process better than others). See page 17 of Bamboo in the Laboratory.
- Heat treatment (at 302 degrees Fahrenheit) causes an initial dimensional shrinkage in the Bamboo of a little more than 1.5%. Within 20 days (concurrent with reabsorbing moisture), this shrinkage has reversed and becomes relatively stable at a shrinkage of slightly less than 0.5% of the original dimensions. See Figure 9 page 1 of Bamboo in the Laboratory and associated findings.
- Utilizing a heat treating temperature of 180 degrees Centigrade (356 degrees Fahrenheit) for 18 minutes will optimize the Breaking Strength and Bending-to-Break Point, without approaching too closely the 200 degree Centigrade (392 degrees Fahrenheit) point at which the higher temperatures cause a disastrous drop in these two values. See Figures 15 and 16 on page 16 of Bamboo in the Laboratory and associated findings.