Iron alloyed with various proportions of carbon gives low, mid and high carbon steels. It can be alloyed with gallium arsenide to produce ternary and quaternary semiconductors. Polonium alloyed with beryllium provides an efficient neutron source. Tungsten shot is often alloyed with nickel and iron, softening the base metal. They may be forged out of alloyed or unalloyed tool steel. The nickel-based blades are alloyed with aluminum and titanium to improve strength and creep resistance. Oxygen-free copper can be alloyed with phosphorus (CuOFP alloy) to better withstand oxidizing conditions. Indigenous South Americans had full metallurgy with smelting and various metals being purposely alloyed. Different ores or metal bars can be alloyed together for higher quality materials. It has low mechanical strength compared to more significantly alloyed metals. Tin is most commonly alloyed with copper. Many ancient civilizations alloyed metals for purely aesthetic purposes. Copper is often alloyed with precious metals like gold (Au) and silver (Ag). These 3 metals can be alloyed with each other and with aluminium. Metallurgy of bronze and pseudo-bronze (alloyed with arsenic instead of tin).