Brass and copper must be "work hardened". "Working" can be bending, hammering, rolling, etc. -- anything that mechanically moves the metal. Just the microscopic movement of a boiler "inflating" during the first steaming will harden the copper back to a safe state.
In your case, it's going to be very hard to do. The only way I can think of to harden it would be to tumble polish or sandblast it. Tumbling could be difficult in the scales we work in, though not impossible. My dad built a 1-ft diameter rock tumbler once from a discarded piece of iron pipe. The base was 2x4s and an old washing machine motor powered the revolving shaft that moved the tumbler body. It would have accomodated a brass cab. If you don't want to go to that length, then blasting with glass beads or another non- abrasive medium should give you some hardness back. If it's just the joints where you soldered together the walls, you might even be able to stiffen it up enough by gently twisting and shoving it in your hands. As Harry noted, soft solder is perfectly fine for parts like this. They don't get hot enough to require silver soldering. regards, -vance- Vance Bass Albuquerque, New Mexico, USA Small-scale live steam resources: http://www.nmia.com/~vrbass
