Bullion is non-ferrous metal that has been refined to a high standard of elemental purity. The term is ordinarily applied to bulk metal used in the production of coins and especially to precious metals such as gold and silver. It comes from the Anglo-Norman term for a melting-house where metal was refined, and earlier from French bouillon, "boiling". Although precious metal bullion is no longer used to make coins for general circulation, it continues to be held as an investment with a reputation for stability in periods of economic uncertainty. 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.