You can identify authentic sterling jewellery by looking for a mark on the jewelry. The law states that authentic sterling silver must be marked ‘Sterling’ or ‘925’. This engraving is done when the genuine silver is crafted and is typically engraved on the clasp of necklaces or inside of a silver ring or silver bracelet. If the authenticating mark is not present, the chance that it is genuine is extremely rare.
Examine the coloring of the item very closely. Sil. plated jewelry is generally shinier and warmer in tone than genuine silver. If it shines too much or you see parts of the jewelry where the silver looks like it has worn off, the piece of jewelry is possibly silver plated and not authentic.
Authentic silver gets oxidized and tarnishes when kept in open air. Using a light-colored and soft piece of cloth, rub the surface of the item. If you find black marks on the cloth, then the item is very possibly authentic.
Take the piece of jewelry to the jewelry shop and ask them to test it by applying nitric acid to a non-conspicuous spot. The acid will discolor unauthentic silver due to the high content of copper and will leave a permanent green spot. This is a sure test for silver-plating and for disproving authenticity.
To be completely sure, make sure you purchase your sterling jewellery from a trusted source like a neighborhood jeweler or a reliable online jewelry retailer. Also try to check out the reputation of the jeweler by asking friends, family and acquaintances. Trusted jewelers can appraise any piece of jewelry, like a bracelet or ring, you currently own, and tell you if they are fake or not.