How do you know if the gold item you have is really gold? You can buy acid testers that are sold on ebay for around ten dollars. How to use the acid. Usually they come with a stone. You take the gold item and scratch it on the stone. You should see the color on the stone. Pour a drop of acid on the stone where the gold color is. If it stays after the acid is poured onto it , it is gold! If the gold color dissapears in front of your eyes , then it is not gold!