From Mine to Ring: The Journey of a Diamond

A diamond in a ring has already travelled further than its wearer probably has. Born deep in the earth, in most cases more than a billion years ago, mined from volcanic rock, sorted in the rough, cut over weeks, graded in a laboratory, and set at a bench, the stone passes through more skilled hands than almost any other object you will ever buy. Here is that journey, stage by stage, and it starts with a simple question: how are diamonds formed?

How are diamonds formed in nature?

Natural diamonds form in the earth’s mantle, mostly at depths of about 150 to 250 kilometres, where heat and pressure compress carbon into the hardest natural material known, and most are between one and three and a half billion years old. They reach the surface through kimberlite pipes, volcanic channels that carried the stones upward in eruptions long before recorded history, and the great mines are dug into these pipes. Rivers and the sea later carried some stones far from their source, which is why diamonds are also recovered from river gravels and off the Atlantic coast. The best known South African pipe was found at Colesberg Kopje in 1871, a story told in full in the Kimberley rush history.

The Mine

Ore is crushed and passed through heavy media separation, because diamond is dense, and grease belts, because diamond sticks to grease while the waste rock does not. X ray sorting machines do the final pass. The rough is then sorted for sale: De Beers divides its own into more than twelve thousand categories by characteristics such as colour and clarity. The honest point to remember is that a rough stone gives little away about how it will look once cut. Most mined diamonds are industrial grade, used in cutting, drilling and polishing tools. Only a fraction become jewellery stones, which is the first explanation of why gem quality costs what it does. The history of diamond mining in South Africa, and what it did to the country, is told in how diamonds shaped South Africa’s history and economy.

The Cutting Centre

Rough stones go to cutting centres, where the same trade has been practised for centuries. The cutter’s first decision is the plan: which shape the stone will become, and how much weight survives the cut. The round brilliant, with its 57 facets, is the classic shape, and cutting one usually sacrifices the most weight, which is part of why it carries a premium. Fancy shapes preserve more weight, though each makes its own demands on the material. The cutter’s craft, step by step, is in how a rough diamond is cut and polished, and the four grades that result are explained in our four Cs guide.

The Laboratory

Finished stones go to a grading laboratory, where gemmologists assign the colour, clarity and cut grades, and the report number can be inscribed on the girdle with a laser. The certificate is the stone’s passport: it records what the stone is, and it follows the stone for life. GIA, which created the four Cs, is the laboratory many buyers look for, and a good jeweller can verify the inscription against the certificate in front of you, which is the check described in the diamond buying guide.

The Setting Bench

The last journey is the shortest and the most personal. The jeweller takes the certified stone, designs the setting, and sets the diamond by hand, a process of measurement, metalwork and pressure tolerance that cannot be rushed. This is the stage where a workshop on site matters most, because it is the one stage the buyer can usually watch. At Prins & Prins the setting bench is part of the same building as the showroom, and the bespoke process guide walks the full design sequence.

Why the Journey Affects the Price

Every stage adds skill, and skill costs. Mining adds the cost of extraction, cutting adds the cost of the weeks spent at the wheel, grading adds the laboratory, and setting adds the jeweller. None of these stages are optional, and none of them are visible in the finished ring, which is why two identical certificates can sit at very different prices depending on who did each stage and how well. The economics are laid out plainly in diamond prices by carat.

What to Ask a Jeweller About the Journey

A good jeweller can tell you the stone’s origin story, its cutting provenance and its certificate history. Ask. The answers separate a house that knows its supply chain from one that bought a parcel and hopes. And if you want to see the journey compressed into one building, the Museum of Gems & Jewellery at Huguenot House shows the rough, the tools and the finished pieces side by side, ending in a working goldsmith studio. Entry is free, by appointment.

Sources:

• Gemological Institute of America: Recent Advances in Understanding the Geology of Diamonds

• Gemological Institute of America: Diamond Description

• De Beers: The Diamond Journey