Short answers, pulled from the story.
Scholars define a brass instrument by the method of sound production called labrosone, which requires the player to vibrate their lips against a mouthpiece. This physical action determines the family classification rather than the metal or wood material used to construct the instrument.
Arban published a method in 1864 that established three valves as a core standard layout for most modern instruments. Natural brass instruments without valves existed before about 1795 for trumpets and 1820 for horns but could only play notes within the natural harmonic series.
Cylindrical bore instruments maintain a constant diameter throughout their structure and produce a brighter, more penetrating quality. Conical bore instruments feature tubing with a constantly increasing diameter from mouthpiece to bell and create a mellow sound found in British brass bands.
Pressing valves lowers pitch but creates intervals wider than desired when combined because the added tubing lengths alter the acoustic physics. The first valve adds one step while the second adds two steps, resulting in sharpness for certain notes that players must adjust using lip control or mechanical compensation systems.
Traditional construction involves polishing brass and applying lacquer to prevent corrosion, though higher quality instruments sometimes feature gold or silver plating instead. Plastic emerged as an alternative material in the 2010s for cheaper and more robust options that come in almost any color.