Ah, period instruments. My main gig is performing on period instruments. Not as old as natural trumpets, but early valved instruments, mainly those used in the mid 1800's in the U.S. Yes, I play in a "Civil War" brass band. We use authentic period instruments and play the original music (although we've reprinted it to make it readable). Quite a unique sound - nothing like today's brass instruments. A very smooth, mellow sound. They're all rotary valve and extremely conical in nature. It seems that piston valves were more popular in Europe than in the U.S. at the time.
Each instrument has its own intonation problems, and the group as a whole has others, given that these instruments were designed to different pitches. Back "in the day", bands would buy entire sets of instruments from the same manufacturer to at least insure that they could be tuned with each other. We don't have that luxury, and have gone through quite a few horns to find a set that will tune together. Even so, the bass has his slide in as far as it will go, and the Eb cornet and the Bb cornet (me) have their bit and slide out almost as far as they will go.
To play these instruments "well tempered" requires an intimate familiarity with the horn you're playing, and an awareness of problem notes in the other instruments. It's a constant battle with alternate fingerings and lipping, but we can generally pull it off.
Some groups such as ours use reproduction instruments which play much better in tune (at least the good reproductions do), but also have a more modern sound. Others just play the old music on modern instruments. These two options probably result in a better-in-tune, "nicer" performance, but that special sound's just not there. I feel that a proper historic presentation should come as close as possible to the original sound and style. The antique instruments and original music achieve the sound, but the style is open to some debate, as there are no period recordings. The best guess may be to listen to some of the earliest recordings from the 1900's of cornet soloists.
BTW, I even became somewhat proficient on a borrowed Eb keyed bugle a few years ago, but the owner sold it.
Now, that's a different sound. A horn full of holes. Here's a pic of my period Bb cornet. Made by Henry Lehnert in Philadelphia shortly after the Civil War, solid German silver, "Allen" style pinched rotary valves. A very nice horn! Go to our web site for photos and descriptions of 20 or 30 more instruments we have.
www.otbrass.com 
