Elmwood's 30.10ct diamond solitaire: read the grading report before the estimate
Elmwood's 30.10ct diamond solitaire: read the grading report before the estimate
A large London auction stone this week is a useful reminder that a diamond's price rests on several grades, and weight is only the start.
London auction house Elmwood's is set to offer a 30.10ct white diamond solitaire at its Fine Jewellery auction on November 11, as reported by Retail Jeweller. The estimate is between £900,000 and £1.2m.
A solitaire is a piece set with a single diamond. "Ct" stands for carat, the unit used to weigh gemstones. An estimate is the auction house's guide to the range it expects bidding to reach. It is a guide only. The final hammer price, the winning bid when the auctioneer's hammer falls, will only be known after the sale.
The report gives the weight, the estimate and the sale date. It does not give the stone's colour, clarity or cut grades. Those details matter a great deal. Anyone following the sale should look for them in Elmwood's own catalogue and avoid guessing.
Why weight is only part of the price
Carat weight tells you how heavy a diamond is. On its own, it says little about how the stone looks or how rare it is. Two diamonds of the same weight can sit far apart in price. The difference comes from the other grades on the report.
Colour describes how close a white diamond comes to having no tint at all. Stones with less visible yellow or brown tend to command more.
Clarity describes the natural marks inside a stone, called inclusions, and on its surface, called blemishes. Fewer and smaller marks usually mean a higher grade.
Cut describes how well the stone has been shaped and faceted. Facets are the small flat surfaces polished onto a diamond. A well-cut stone returns more light to the eye. Reports often grade polish and symmetry separately. Polish covers the finish of those surfaces. Symmetry covers how evenly they line up.
Fluorescence is a glow some diamonds give off under ultraviolet light. Reports note it, and buyers often weigh it into their decisions.
The setting and its metal also add to the value of a finished piece, as does its condition. With a stone of this size, though, the diamond's grades will carry most of the weight.
The certificate comes first
A grading report, often called a certificate, is a document from an independent gemmological laboratory. It records the stone's measurements and grades. It usually carries a report number. Many laboratories also inscribe that number on the girdle, the thin outer edge of the diamond, using a laser.
The report is what lets buyers compare like with like. Without it, an estimate or a price tag has nothing solid to stand on. Grading standards can differ between laboratories, so the name of the issuing laboratory matters as much as the grades it records.
What this means for luxury watch and jewellery buyers
This sale is a single event involving a single stone. Its result, whatever it turns out to be, will not set the value of other diamonds. Every stone is priced on its own grades, its certificate and its condition.
The same checks apply to any diamond you consider, large or small, at auction or in a shop. Read the report before you look at the price. Then compare stones only when their reports match closely.
Checks to make on a diamond grading report before comparing prices
- Confirm which laboratory issued the report, and check the report number against that laboratory's online records.
- Read the colour, clarity and cut grades together, along with polish, symmetry and fluorescence.
- Ask whether the report number is inscribed on the stone's girdle, and have a jeweller confirm it matches.
- Check that the measurements and weight on the report match the stone in front of you.
- Compare prices only between stones whose reports show closely matching grades.
If an auction catalogue or a seller does not supply a grading report, ask for one. If the grades are missing, treat any price or estimate as incomplete information. A calm, careful reading of the paperwork protects you whatever the size of the stone.
