Although tarnished brass doesn't have much of a shiny lustre, when cleaned and well-polished, it can look just similar enough to gold to cause problems for the unsuspecting buyer. Gold, as a precious metal, is much more expensive than brass; this fact provides a big incentive for con men to try to pass off brass imitations as gold jewelery and sell them for a huge profit. To avoid being duped this way, there are a few simple tests you can use to identify clearly from which of the two metals a given object has been made.
Measure the object's length, width, and height, then multiply them together to find its volume.
Weigh the object. Divide the object's weight by its volume to find its density.
Compare the density you calculated to the density of gold (19,320kg per cubic meter, or 19.32 grams per cubic centimetre) and the density of brass (8,400 to 8,700kg per cubic meter, or 8.4 to 8.7 grams per cubic centimetre). Gold is more than twice as dense as brass; a similar-sized gold object will be that much heavier. If the density you calculate is too much for brass but not quite enough for gold, the object may be made of gold alloyed with a lighter metal.
Use Schwerter's salts. These are a chemical solution available through jewellers and jewelery suppliers. To use them, find a surface of the object that you can scratch and scratch it deeply with a file. Add a drop of the Schwerter's salt solution. If the metal is brass, the scratch will turn brown. If it is gold, there will be no change in colour.
Try to poke a pin into the object. Gold is a very malleable metal, and you will be able to press a pin into it. Brass is harder and will not hold the pin.