The quality of the gemstone itself is obviously an important factor, but so is the design.

“Iconic jewellery pieces or recognisable motifs by a brand from a particular period generally hold their value well,” said Cristel Tan, international jewellery specialist for Phillips Southeast Asia. These include Cartier’s Art Deco jewels and Tutti Frutti designs, and Van Cleef & Arpels’ iconic Zip necklace.

“Contemporary jewellers like JAR and Bhagat also stand out for their creative designs and exceptional craftsmanship. Produced in extremely limited quantities for a select clientele, these rare pieces always create a buzz of excitement when they come up for auction.”

It’s also best to keep the jewellery as is. “Collectors tend to gravitate towards pieces that are kept in their original form, unless the changes have been recognised by the original designer,” she advised. Provenance also plays a part.

“Famed jewellery collectors such as Elizabeth Taylor or the Duchess of Windsor tend to incentivise collectors to own a piece from their notable collections.” Provenance also extends to the stones themselves. Spinels from Burma for instance, will cost more than spinels from Sri Lanka, even if they are visually identical.

Once you understand the value of your stone, it doesn’t really matter whether it’s a loose rock or in a piece of jewellery. According to Shiu-Fang Chiang, vice president and senior specialist at the jewellery department of Christie’s Asia Pacific, “Buying a loose stone lets you examine the gem thoroughly, and set it whatever way you like, while a finished piece of jewellery will show better brilliance and colour thanks to the effects of its mounting and side stones. But you must be careful of defects that might be hidden by such settings, such as a flaw under the prong, or a painted bottom to enhance the saturation. If there is any uncertainty, request to unmount the stone if possible.”