Posted by John Swensen on January 26, 2000 at 16:01:39:
In Reply to: Re: Mouthpieces posted by Rick Denney on January 26, 2000 at 13:47:58:
I would just like to add a few points to Rick's helpful information.
Brass is just about the easiest metal there is to machine (especially free-machining brass, which contains a few percent lead that encourages the brass chips to break off cleanly; your mouthpiece is, almost certainly, leaded brass, although your bell probably contains no brass). Brass tarnishes, however, so it is usually plated. Its specific gravity (s.g.) is about 8.4 (8.4 times the density of water).
By adding about 15% nickel to the brass, it becomes nickel silver (or German silver), even though there is no silver in the alloy. It machines about as easily as brass, and there are leaded alloys, as well. Nickel silver does not tarnish very fast, and it has been used, unplated, for some horn mouthpieces.
Bronze is much harder and stronger than brass, and is relatively difficult to machine.
It also tends to tarnish, and has an s.g. of about 8.8.
Most alloys of stainless steel range from difficult to very difficult to machine, and generally require large, heavy, rigid machinery to be able to cut fast enough to avoid work hardening. Stainless steel will not corrode or tarnish in the kinds of environments that mouthpieces encounter, and it can be electropolished (kind of like reverse plating) to produce an extremely smooth surface (far smoother than most new, gold-plated mouthpieces). Specific gravities of stainless steels range from about 6.2 to 6.5. Stainless steels also have a thermal coefficient of expansion very similar to that of brass, which is one reason why it is used for pistons in Nirschl valves.
Some steel alloys (particularly the leaded, free-machining steels) are cheap and easy to machine, but have specific gravities around 7.9. It also rusts, and must be plated for
Many alloys of aluminum are easy to machine, and can be anodized cheaply and easily, but their densities are about one third that of steel.
Most alloys of titanium make stainless steels seem easy to machine, and are frightfully expensive as well. With a density about 60% that of steel, with strengths as high as the strongest steels, and with superb corrosion resistance at high temperatures, it is an ideal aerospace alloy but, apart from a few experimental flutes and valve rotors, it hasn't had much use in musical instruments.
In my opinion, silver or gold plating on brass is close to ideal for mouthpieces. If you want to slow down the wear rate, buy an eighth of a yard of silver cloth at a fabric store (a dark brown flannel used to keep silver tableware from tarnishing in storage) and sew up a few bags for your mouthpieces. You can use the bag inside a mouthpiece pouch and you can set the mouthpiece on the bag, instead of directly on a stand or a table.