Bullion is gold, silver, or other precious metals in the form of bars, ingots, or specialized coins that is said to maintain its worth better than conventional currencies and is therefore kept as a form of emergency currency by both governments and private citizens alike. The word "bullion" comes from the French word bouillon, which meant "boiling", and was the term for the activity of a melting house which creates the ingots or bars from the raw material. The value of bullion is typically determined by the value of its precious metals content, which is defined by its purity and mass. To assess the purity of gold bullion, the centuries-old technique of fire assay is still employed, together with modern spectroscopic instrumentation, to accurately determine its quality to ensure that the true worth of the bullion is paid out; maintaining its security as an investment.