1 Inspection by eye. 3 Testing the composition of the metal. By Eye Most fakes are cast, not struck, usually in two parts and joined together. Because the moulds have usually been made by taking an impression from a real coin, this furthur reduces the sharpness of the image. Ancient coins often have striking cracks - splits in the flan where it has spread under the impact of the hammer.
Casts are sometimes slightly smaller than the original, due to shrinkage in the moulds.
The second test, not always available to collectors on a modest budget, is to check the weight on accurate scales. This is not a certain indicator, because when coins have been in circulation they become lighter, and very often they were made within a weight-range rather than with modern exactness. I have a perfectly genuine Gallo-Belgic E Celtic coin that is lightweight, which belongs to a series believed by many to have been issued in a great hurry to pay for resistance against Caesar in the Gallic War. These coins show quite considerable weight variation, and lightweight coins may well have been issued late in the production when metal supplies were running out. If the coin is far too heavy or light, it should be suspected of having a core of another metal and being plated.