A superbly crafted and designed sapphire and diamond Art Deco ring, for sale here

What makes a good piece of antique jewellery? Why are some jewels more desirable than others? And what is a piece really worth? These are questions that new and not-so-new collectors ask themselves constantly.

The short answer is that a jewel is worth as much as you are willing to pay for it. Jewellery is decoration: it satisfies a basic desire for adornment in humans – and every person is unique in his or her appreciation of beauty.

Yet long ago I noticed that as a dealer and collector I use a rough mental checklist of seven factors I consider whenever I am buying. I thought I’d run you through them – I hope they’ll help you too.

My jewellery-buying checklist:

1. Authenticity: my first criterion. There are so many reproductions around today, and some of them are very good. South America, in particular, is producing a vast amount of them; so is Portugal, along with several other countries. It really does take many years of buying to pick what can be extremely subtle differences between reproductions and genuine antiques. You may want to buy from someone knowledgeable who will guarantee the age of piece. That won’t always be the most expensive jewellery shop in town.

2. Condition: a main driver of prices in antique and vintage jewellery. There are a lot of damaged old pieces out there and the more damage there is the more their worth tumbles. If a piece is very rare or very old a little damage may be acceptable. Minor, difficult-to-see dings will affect the value less than obvious blemishes. But beware of hidden faults not easily seen. It can be reassuring to buy from dealers who will stand behind the soundness of their pieces.

3. Design: imagine what a jewel would look like as a drawing.
Consider here the arrangement of the component elements, the choice of colours and materials, and the surface treatment – whether solid, worked or using negative space.

4. Materials: these give a jewel its intrinsic value. What you would pay for the gold, diamonds and gemstones that were used to create it? When high-quality components are present it is often a sign that other factors such as design and workmanship will be good – the maker will not want to have squandered valuable materials. But of course that’s not always the case: we have all seen beautiful stones in ugly settings and poor materials in a beautifully worked pieces.

5. Rarity: an obvious factor in value. The price for good antique earrings is very high owing to their rarity. (My previous blog, on antique earrings, explains why they are so scarce). Georgian and earlier jewellery can command astronomical prices because so few pieces survive from so long ago – a time when few people outside the nobility wore jewels. Rarity has to be combined with wearability, though – the next consideration on the list.

6. Wearability: this comes down to fashion and depends on place and time. A few years ago it was extremely difficult to sell anything with an inscription or a monogram. Now such pieces are being avidly collected as repositories of history. And brooches are for the most most part out of fashion – so are relatively underpriced because of it. In Australia some years ago there was a huge fashion for women wearing men’s watch chains as necklaces. Prices soared accordingly. Now most are languishing in jewellery boxes and are worth far less.

7. Workmanship: this comes down to the jeweller’s skill in transforming raw elements into a harmonious whole – where the human hand works a metamorphosis. Occasionally jewellers who are true artists emerge. Lalique, perhaps, was the greatest of these. But there have been many including Castellani, Fabergé, Giuliano and Cartier, just to start.

So that’s the full checklist. Every jewel will score more highly on some factors than on others.

For example, a low-quality diamond in a cheap cast ring setting might be worth less than a Bakelite necklace. The diamond might outscore the plastic in terms of the materials’ intrinsic value, but an original necklace in a rare design and pristine condition could still be the more appealing piece of jewellery – and thus more valuable.

You should, of course, buy what you love. But educate yourself, too. A 10x loupe could be your best new jewellery friend. And there are several excellent jewellery reference books available. If you can’t afford to collect them, your local library may be worth a visit.

Finally, do speak to jewellery dealers. Ask questions! For my part – as followers of my @karendeakin.antiques Instagram account will be aware – I absolutely love to share my knowledge with my fellow jewellery lovers. Please do shoot me an email: if I can help I will.