Answer to Question 1
Gamelan instruments are not tuned to a fixed, standard pitch as in the Western music-culture where the A above middle C is taken to be at exactly 440 cycles per second. Rather, the tuning of the instruments in each gamelan is unique; instruments are very carefully tuned for the particular ensemble in which they are being used. Bronze gamelan instruments may require periodic tuning which, in turn, requires a long process of hammering, filing, and intuitive experimentation by experts.
Answer to Question 2
Bronze is the preferred metal for gamelan manufacture, due to both its durability and sweet sound quality. Brass and iron are also used as cheaper metals, but instruments made of these metals sound less sonorous. The process of manufacturing bronze gamelan instruments is lengthy, requires great skill, and may begin with ritual preparation by the smiths.