Seventy carats, no reserve, on the block at Bonhams

§1The dare in the catalogue.

The arithmetic is the hook. When Bonhams sells its California Jewels auction in Los Angeles on July 28, the marquee lot is a 70-carat diamond necklace of pear, oval and marquise stones estimated at up to $50,000, and offered without reserve. Seventy carats of graded diamond for the price of a single fine solitaire is not a market on the diamonds; it is a market on the setting, the certification and the story.

That is the estate logic of a no-reserve sale. Older mounted pieces, whose individual stones are hard to certify and expensive to break out, trade at a steep discount to the loose-goods price sheet, and a seller who wants a clean, guaranteed sale accepts it. The estimate is a floor to walk in the door, not a valuation of the carats, and the room, not the book, sets the price.

§2Estate logic.

The catalogue runs deeper than one lot. Bonhams lists more than 300 jewels including a 1920s necklace built around a 7.10-carat diamond at a $35,000 high estimate, a necklace set with 34.95 carats of multicolored sapphires and 4.20 carats of diamonds at $28,000, and three unmounted diamonds estimated between $35,000 and $50,000, with signed pieces from Van Cleef & Arpels, Graff and Boucheron threaded through the sale.

§3What the day sale measures.

The venue is the point as much as the goods. A California day sale is where the accessible middle of the jewelry market clears, the estate and secondary material that never reaches a Geneva evening, and it is a fair gauge of what ordinary collectors will pay in a summer when the metal underneath every lot has rarely been dearer.