The Jonker Diamond is one of the great twentieth-century rough finds. Discovered in January 1934 on the alluvial claim of Jacobus Jonker on the Elandsfontein farm near Pretoria, Transvaal, the rough weighed 726 old carats, equivalent to 725.65 metric carats, and was a clean, slightly off-white stone of remarkable transparency. It ranks among the largest gem-quality alluvial diamonds ever recovered.

Discovery

Jacobus Jonker was a small-scale digger who had worked his Elandsfontein claim for many years. The diamond was found by his son just after a heavy rainstorm. The Diamond Corporation purchased the rough for approximately seventy-five thousand pounds sterling, a sum that transformed Jonker's circumstances and was widely reported in the international press. The stone was insured for one million United States dollars when it was sent to London and then to New York, an event that drew large crowds at every stop.

Sale to Harry Winston

The Diamond Corporation later sold the rough to Harry Winston of New York for a price that has been reported variously at around seven hundred thousand United States dollars. Winston's acquisition of the Jonker, only weeks after he had founded his own house, was the first of the spectacular major-stone deals that built his reputation as the leading dealer in important diamonds of the mid-twentieth century.

Cutting

The rough was studied for almost a year by Lazare Kaplan, who had been engaged by Winston to plan and execute the cutting. Kaplan eventually divided the stone into twelve cut diamonds. The principal stone, the Jonker I, originally weighed approximately 142.90 carats as an emerald-cut and was later recut to 125.35 carats. The remaining eleven stones included emerald cuts, marquises and pears in a range of sizes from a few carats up to roughly forty carats. The cutting was completed in 1936 and was widely covered in the trade press as a textbook example of careful planning of an exceptional rough.

Subsequent ownership

The Jonker I passed through several distinguished hands. Winston sold it to King Farouk of Egypt in 1949, after which it was reported in the collection of Queen Ratna of Nepal, and later in private hands in Asia. The smaller Jonker stones dispersed through the international trade and several have appeared periodically at auction. Tracking individual Jonker stones through the secondary market is complicated because Lazare Kaplan's original cut weights were not always retained when stones were later recut to suit changing fashion in proportions.

Significance

The Jonker is significant on three grounds. It demonstrated that South African alluvial workings, not only the kimberlite mines of the Big Hole and Premier, could still produce stones of historic size in the twentieth century. It established Harry Winston's standing in the great-stone market and inaugurated his firm's long association with named historical diamonds. And the cutting of the rough, with Kaplan's slow study and the eventual yield of twelve stones, became a reference case in cutting literature for how to plan a very large piece of clean rough. The Gemological Institute of America has cited the Jonker repeatedly in its treatments of historic diamonds.