Cartier is one of the most commonly reproduced jewellery and watch makers, in part because an authentic piece can cost up to £32,500, based on 2010 prices. Cartier made several types of jewellery, including rings and necklaces, usually with a diamond or multiple diamonds on the piece. Reproductions and fakes use diamond style jewels, which make the piece worth even less than the price it sells for. Not all pieces were clearly marked, but it's still possible to identify a real Cartier ring.
Check the box, if the ring came with a box. Cartier used specially branded boxes for all its jewellery and watches and if the piece has its original box, you know that it's a real ring. Most dealers offering reproductions omit the box or give you a generic box. In some cases, the box has Cartier on it, but the poor quality is a tip off that it's not authentic.
Compare the ring against pictures on the Cartier website. Cartier lists photographs of newer pieces on its site, which lets you compare your ring against modern day pieces. The style of the piece and the metal used, should be similar.
Look for auctions taking place that offer Cartier rings and jewellery. Sometimes the easiest way to compare your ring to others is by seeing authentic rings in person. Check the markings inside the ring, as well as the style and tool markings on the ring and compare those to yours.
Read any writing found inside the ring and look for spelling errors. Reproduction pieces are sometimes made in foreign countries, where words are spelt differently or misspelled completely. If you notice that your ring has letters missing or extra letters, it's probably a fake.
Examine the inside of the ring, looking for a mark that indicates the maker or the carats. Cartier ring makers often signed the inside of the ring by listing a design or logo. Also, look for a copyright date or manufacturing date, which indicates when the piece was made.
Only take your ring to authorised retailers of Cartier pieces or dealers with experience selling antique pieces. It's very rare for a new piece to lack an identifying mark, but older pieces sometimes slipped through without the Cartier name. Authorised sellers know how to identify the ring, even if it lacks the right markings. Consider taking the ring to a well-known auction house, such as Sotheby's or Christie's; both of which offer jewellery sales and specialise in higher-end pieces. The appraisers working for the auction house can identify your ring and give you its value.