I saw a baroque ensemble play last night; the group included 2 guest soloists, one who played the sackbut and one who played the natural trumpet. I had never heard of these instruments before, and though the sackbut looked much like its successor, the trombone, the natural trumpet didn't look much like a trumpet. It had no valves or keys, and it was much longer.
The homepage of the Philadelphia Natural Trumpet Ensemble (http://www.intr.net/bleissa/lists/pnte.html) says that the natural trumpet is an "8-foot cylindrical bore instrument", which means nothing to me, though 8 feet is very long. The MHN Music Encyclopedia (http://www.si.umich.edu/CHICO/MHN/pages/naturaltrump_gnrl.html) provides a bit more comprehensible information, explaining that what makes the natural trumpet natural is precisely the lack of telescoping slides (see sackbut or trombone) or valves (see trumpet). "Lipping techniques" are how experienced players produce different tones than those inherent in the instrument itself.
I must admit this doesn't make much sense to me, but the concert, played in an old chapel in Toronto, was very lovely.