Many years ago, at the home of Philip Farkas, I held in my hands a copy of the mouthpiece of Dennis Brain. Farkas was actually at one point (before his association with Holton) working with Schilke and Brain to potentially market a copy of his mouthpiece. My main memory is the small inner diameter and the thin rim. These two elements are parts of the puzzle of all that made his playing great.
Dennis Brain’s mouthpiece was, by modern comparison, a small affair. The old silver threepenny bit (which hornplayers used to carry as a measuring device) would not even lie in the cup, but stood, so to speak, half out of it. This I verified on several occasions as Dennis sometimes experimented with different mouthpieces, but (let me hasten to add!) always the same rim. (The type that used to be known as the ‘Busby’ mouthpiece – named after Tom Busby, a well known London horplayer of the 1920s).
This mouthpiece above would appear to have that same rim, and came to Arizona associated with the Hawkes piston valve horn owned by Arizona State University (more here). It is marked Hawkes & Son London with the letter B stamped on side. The inner diameter is very small and would only suit someone with quite thin lips. It fits the crooks on the Hawkes horn well and tightens up sound production, but does not fit a modern horn, especially not one made for a European shank mouthpiece such as the Alexander horn later used by Brain.
The second photo shows the rim compared to the more modern rim of a Holton XDC. Where the differences come in has to do with sound and sensitivity. It has a small sound but is at the same time very sensitive and must have fit his unconventional embouchure very well.
The above is a portion of the text of a lecture-recital presented at the 2011 International Horn Symposium in San Francisco. A full article version of the session is in preparation. The reference on the information that Farkas/Schilke planned to sell a copy of his mouthpiece is from the Nancy Jordan Fako book on Farkas. For more on the horns Dennis Brain played and on the IHS session I presented see this article.