Until pretty recently virtually all French horn mouthpieces were made of brass (plated with a layer of silver or gold — with a very small number made from solid nickel silver or from plastics). But in recent years, with the use of CNC lathes for mouthpiece production, stainless steel has become a viable option. How do brass and stainless steel compare?
I have wondered this for a while, and only recently had mouthpieces to use that were actually exactly the same to compare back to back. The results are rather interesting, as depending on what mouthpiece and on what horn it is easy to observe different results.
Every dimension of a mouthpiece makes a difference, as does the interface with the instrument (influenced by shank size). And then you layer on top of that a difference of materials! The biggest differences are obvious at very high dynamics. Sometimes I find that brass sounds better; other times the stainless steel was certainly better; yet other times I am hard pressed to say much more than the sound was slightly different but neither was really better than the other. Just different.
The other place I really notice differences is how the articulations sound, with stainless being crisper by a degree, but on some horns and with some players it comes across as harsh rather than crisp. In other words it depends somewhat on how you play to begin with and the tendencies of your horn.
The “envelope” of the sound is a bit different to be sure, but if one material is generally better than the other I am going to say officially is hard to say. Again, it depends a lot on the player and the type of horn and mouthpiece they were using.
One thing I can say broadly on this topic is that the temper (hardness) of the stainless steel mouthpiece is undoubtedly much harder than the average brass mouthpiece you have been using. Having loaned out a few mouthpieces over the years I can say with certainty that the stainless steel mouthpieces in particular are very resistant to showing any sign of wear, they look brand new for a very long time.
Another point worth mentioning in passing, the stainless steel mouthpiece should be exactly up to spec as produced. A brass mouthpiece that has been plated will always be slightly different than it was before it was plated, as the silver or gold can/will be distributed over the surface of the mouthpiece slightly unevenly. Thousandths of an inch matter in mouthpieces.
I am inclined to say the stainless steel mouthpiece may play a little easier in general if I am comparing two that are identical (brass compared to stainless), but of course your perception may be different than mine, and for a fair comparison they really do need to be identical mouthpieces by the same maker. My comparisons have been with mouthpieces produced by Houser, which is a good place to start if you are considering trying out this new material and have not yet done so.