By Steven Wasser - President, Verne Q. Powell Flutes, Inc.
These are photos of two sterling silver pieces which have been joined using two different techniques. The photos were done at MIT using an electron microscope.
The top portion of the photo to the right shows a joint that has been made using high temperature silver braze at around 1400°F. The bottom portion of the photo shows a joint that has been made using low temperature solder at around 450°F.
Does this affect sound? Yes! The high temperature silver braze inter-diffuses into the sterling silver, and the result is a piece of metal that acts as if it were a single piece of metal. The low temperature solder acts more as metal glue and sits in between the two layers of metal. In my experience vibration and resonance are superior when only a single, homogenous metal is involved. With the low temperature joint the solder layer can act as a barrier to the transmission of vibration and can dampen response.
What about strength or durability? With a silver brazed joint the musician should never have to worry about things like tone holes leaking or lip plates falling off flute headjoints. The strength of a joint that has been done using low temperature solder is typically 5000 lb/sq inch. The strength of a silver brazed joint is 40,000 lb/sq inch, 8x stronger!
Silver brazing is much more difficult to perform than low temperature soldering due to the high temperatures involved. Also silver brazes contain more precious metal than most low temperature solders and are usually more expensive. For flutes, we silver braze our tone holes, We also silver braze the headjoint lip plate to the wall and the wall to the headjoint tube.