metal Bronze alloys in gamelan instruments can very dramatically between various gamelan makers. Of the makers that use Copper Tin alloys, high tin (greater than 17% by weight) are preferred. Typically the traditional alloys used vary between 20-24% tin by weight. 1) Also the material properties of 20% by weight tin is considered to be the prime material to use. According to Nyoman Wenten the alloy used to make gamelan instruments is varied by the size of the instrument, as a stronger alloy is needed for larger gongs than is needed for smaller bars and kettles, and this variation of recipes is necessary to make instruments that sound perfectly balanced.
A mixture of 30 parts copper to 10 parts tin 2)
According to Nyoman Wenten 30 parts copper to 11 parts tin
10:3 ratio to 5:1 ratio (30% tin to 20% tin) 3)
The more scientifically oriented literature clearly indicates that there is between 20-25% tin by weight in the bronze alloys.
The greater amount of tin present in the alloy increases the hardness of the alloy along with making the tensile strength lower and the alloy more brittle. As tin increases in the alloy the grain sizes in the metal become smaller. It also increases the material density (in theory) but has the drawback of increasing the porosity (amount of air in the alloy) which dramatically reduces density, resulting in the lower density of sand cast blanks used.
Most of the bronze used in gamelan instruments is sand cast at 1100*C and than repeatedly forged at about 600*C, this process has been showed to dramatically increase the acoustic qualities of the material. Forging has been shown to increase the materials density, reduce porosity, and harden the material (work hardening) as well as increase the frequency of the pitches produced. The amount of change caused by forging has the ability to outpace the differences present in various alloys.