Fake coins is a common problem for collectors. A small exercise of calculating the density of the coin can help. Comparing the density with respect to the known value of the metal will help in establishing the claim. For example, if a coin comes with a claim that it belongs to certain period and is of pure gold. Finding the density of the coin can easily establish or refute the claim as it is very common to make fake gold coins where only the outer surface is of gold and inner core is filled with cheap metal. Remember Archimedes.

• Find Weight – Weight can be measured using a weighing balance. Gram is a  reasonable unit to measure the weight of the coin.
• Find Volume – To find the volume, take a graduated or measuring cylinder. These are very common in science labs. Use a cylinder of lower radius but big enough so that the coin can go inside. Fill the cylinder with distilled water to certain mark. Say if it is a 100 ml cylinder then fill the water till 50 ml mark. Drop the coin in it and note the change of water level. If water level is now at 60 ml then the volume of coin is 10 ml or 10 cm³ . Note – 1 ml = 1 cm³ 
• Put the weight and volume in the calculator and find the density. The density will be in g/cm³ 
• Compare the density with reference density of the given metal. Densities of various metals and alloys can be checked here.