Copper is a metal that is only slightly magnetic. Hold a magnet close to the nail and observe any effects. If the nail does not react to the magnet, it might be copper. Powerful magnets may still have a small effect on the nail if it is copper.
Measure the density of the nail by weighing it and measuring its volume. Then, divide the weight by the volume. Copper's density is 8.92 grams per milliliter. If the density of the nail is significantly different than 8.92 grams per milliliter, it is not made of pure copper.
Clean the nail with a mixture of table salt and vinegar. The combination of table salt and vinegar creates the chemical hydrochloric acid, which cleans the nail. Wipe the hydrochloric acid from the nail. If the nail is copper, it will eventually oxidize from exposure to oxygen, water and carbon dioxide from the air. This reaction creates a greenish color on the surface of the nail, similar to an old penny.