The Perth Mint Certificate Programme, which is fully guaranteed by the Government of Western Australia, is the only silver certificate program in the world that is guaranteed by a national government. Trading in Exchange-Traded Funds (ETFs): An investor can have an easy way of gaining exposure to the price of silver through an ETF. The Four Platinum Bullion Coins: A Brief Description Of Each Bullion coins are coins made from precious metals. Their market values are determined by their inherent precious metal contents. As such bullion coins are mainly kept as investments or stores of value. Most of the bullion coins available are made from silver or gold. radiotherapy (particularly of eye tumors). Along with the five other precious metals in the platinum group, ruthenium is generally found in ores in North America, South America, and the Ural Mountains in Russia. Small quantities of this element also occur in pentlandite (an iron-nickel sulfide) obtained from Sudbury in Ontario, Canada, and in South Africa's pyroxenite (an ultrabasic igneous rock) deposits. The term "placer gold", therefore, refers to gold that has formed in rocks moved and placed on stream beds by some geological forces and by the action of water. Lode gold tends to erode from its source, distributing itself naturally among other rocks that have been subjected to similar geological forces. This is especially true in coins of low denomination. Because of this, there exists the possibility of some smelters taking gold or silver coins and melting these down for the scrap value of the precious metals. A couple examples, in this regard, are worth mentioning here: US pennies have been made of copper-clad zinc since 1982, when they were before this time made of copper alloys; and British pennies were once made of 97% copper, but are now made of copper-plated steel. Spectrometry: This method is best used to assay platinum bullion or stock. With the use of a spectrometer or spectrograph, the amount or concentration of a given substance is assessed. The substances are identified through the spectrum they absorb or emit. This assay method has several types. These include absorption, fluorescence, X-ray, flame, visible, ultraviolet, infrared, photoemission, Mossbauer, nuclear magnetic resonance, and Raman.