There are various ways to differentiate a fake gold from a real one. I have outlined some of those ways below.
Price test: The first test of real gold is to do a market survey of the current price of Gold. If the gold item you have is far cheaper then, that may be a sign to investigate more.
Visual test: This can be very deceiving but there is no way to recognize real gold without a visual test. The question then is "How does real gold look like?" First of all, look for some kind of marking. Every genuine gold has a marking showing the karat value. They usually appear as 14k, 18k, 22k and 24k. The karat system is used to express the percentage of pure gold in the item. The higher the karat value, the higher the percentage of gold. This means that 24k is pure gold, 18k is about 75% gold, 14k is about 59% gold while 10k is about 42% gold. Sometimes one may see GP or EP beside the markings. This means that the item is plated with gold. It is just covered with gold. This is not real gold because the gold plating may just be a very thin layer.
It is important to note that gold can come in different colors when they are mixed with different compounds. The examples include white gold which is produced when nickel is mixed with gold; Palladium used to create white gold for people allergic to nickel; green gold when silver is mixed with gold; and pink to red gold when different quantities of copper are mixed with gold.
Real gold has a percentage of sheen but should not be very shiny. When a gold jewelry is extremely shiny, it may not be real gold.
Acid test: The reaction of the item to nitric acid or hydrochloric acid will help to determine whether it is genuine or not. Real gold is not affected or does not form a reaction with nitric acid or hydrochloric acid. Most metals that are usually portrayed as gold when tested in hydrochloric acid form a reaction whereas real gold does not, that is why this has been established as the real test for gold.
Reputable Jeweler: It is always advisable to buy gold from a reputable jeweler because you can always request a test, check the markings and find some good advice about the product which you would not have got.
Discoloration: Fake gold, when worn can either cause discoloration of the skin or discoloration of the jewelry itself. Many people use this method as the simplest way of testing for real gold. And for those that have a warranty, they are simply returned when found to be fake.
Rust: Fake gold rusts in humid temperature, and also over time while real gold does not.
Bite the gold: Gold is soft and when bitten leaves a small mark. Fake gold is very strong and when bitten does not leave a mark.
Weight: Gold has a good amount of density. Put it in water and see the quantity of water that it displaces. The more density it has, the gold is likely present.