There are several ways that gold jewelry is made, and normally the gold content is noted somewhere on the jewelry in a 14K format. There are varying degrees of karats of gold, but by itself, gold as a pure metal is too weak to make jewelry. It is combined with an alloy metal such as nickel to make the metal strong enough to make jewelry. If there is no notation as to the degree of gold in a necklace, there are a few home remedies that you can try to test your gold and see whether it is real.
Place the piece of jewelry on a flat surface. Place the magnet ¼ to ½ inch away from the piece of jewelry. If there is any pull toward the magnet by the piece of gold in question, chances are it is a gold-plated object or it is actually fake gold.
Rub the article of gold jewelry with a jewelry cleaning cloth. If it is gold plated, the plating should come off without much trouble and you will know that the majority of the jewelry is not gold. If there is no change to the piece, or the piece bends under pressure, then you most likely have a true golden piece.
Put the piece of jewelry into a small bowl of sterling silver cleaning solution. Use a liquid cleaning solution instead of a paste for this test. Leave it in the solution for at least 10 minutes. Take the piece out, dry it and lay it on a towel for 24 hours. If it begins to look dull and oxidizes, then you have a piece of fake gold jewelry.
Take the jewelry to a jewelry shop or pawn shop. They will be able to test the density and tell you whether it is true gold or not.