The Coprion Bell

In this article I would like to talk a bit about Conn's "Coprion" bell. Quite a few Conn trumpets, cornets and some trombones came with a Coprion bell. But what is "Coprion", and how does it affect the playing qualities of the instrument?

What is Coprion?
The process necessary for producing the Coprion bell was developed by Conn in 1938. It consists of electrolytically depositing COPper IONns (hence the name Coprion) onto a stainless steel precision form accurate to millionths of an inch (so Conn said in its 1959 catalog), creating a seamless bell. Coprion isn't the same as a "rose brass" or "red brass" bell; these are brass bells with a higher copper content. Coprion is 100% pure copper.
In its advertising for the Coprion bell, Conn showed diagrams of the structure of "ordinary" brass bells compared to the Coprion bell. The brass bell showed an "irregular and hodge podge" crystal structure with comparatively large crystals, while the Coprion bell showed "ions of pure copper side by side in regular, close knit conformation and at right angles to the surface of the metal".

What does Coprion do to the sound and the way the instrument plays?
It is said that on an instrument with a Coprion bell "you can't overblow or 'crack' a note." Also, according to Conn, "Coprion has a special characteristic which permits great dynamic range without change in tone color."
It is generally accepted that high(er) copper content bells make the sound "darker" and have better projection. Jeff Stockham puts it well describing his 1959 10B Victor: "The copper bell also adds projection. This has been borne out by acoustical experiments done by Walter Lawson on french horn bells and by Cliff Blackburn on trumpet bells. Simply put, the high-copper-content bells direct a greater percentage of the energy expended by the player towards the audience, as measured in decibels. The sound of the instrument is less full behind the horn, to the player's ear, but it is richer and louder in front of the horn -- there is significantly increased directional projection. What this means to the player is this: 1) you need to exert less effort to produce a given perceived volume at any point in the performance hall, and 2) the sound remains darker and fuller without becoming shrill or breaking up at high volume levels. So with this 10B I can peel paint off the back wall of the hall if I feel like it, or blow a soaring solo line WITHOUT A MICROPHONE over the top of a screaming big band and still be heard."
The limited experience I have myself with Coprion bell instruments confirms this: it projects like nothing else, the sound doesn't break up or become shrill at high volumes and you can really produce a lot of sound, and the tone color stays more or less the same no matter how loud you play.

Which instruments have a Coprion bell?
Cornets: 12A Coprion, 10A Victor, 28A Connstellation (through serial number 9xx,xxx), 38A Connstellation short model (through serial number 9xx,xxx; beware that there was a 37A Connstellation short model with brass bell), 18A Director and 17A Director.
Trumpets: 12B Coprion, 10B Victor, 38B Connstellation (through serial number 9xx,xxx) 18B Director, 17B Director.
Trombones: 12H Coprion, 10H Victor, 18H Director. Probably the 48H Connstellation (through serial number 9xx,xxx).