Dear Evil Engineer: How many corpses do I need to make the world's largest diamond?

Dear Evil Engineer,

I am heiress to an infamous diamond mining corporation. While I’m keeping busy as founder and CEO of a start-up developing satellite-mounted diamond laser weapons, my father is advancing in years and soon it will be time for me to take over the family business.

I regret that the diamond industry has shed some of its reputation for brutality in recent years, losing credibility as a great sector for talented young villains to work in. I intend to turn things around from day one at the company, beginning by disposing of most of the board of trustees and turning their bodies into the world’s largest diamond. I plan to set the diamond in a crown which I will wear during board meetings, as a reminder to stay in my good books.

How many of them will I need to kill and crush in order to create the world’s largest diamond?

Yours

A bejewelled villain

Dear villain,

An inspired idea! I trust that the corporation will be in capable and ambitious hands.

As you know, diamonds are made up of carbon atoms arranged in a ‘diamond lattice’: a repeating pattern of eight atoms. Creating a diamond takes carbon, and a colossal amount of heat, pressure, and time. Natural diamonds are formed over billions of years within the Earth’s mantle, where they are subjected to incredible pressure and temperature.

This aeons-long geological process can be reduced to weeks or months through highpressure high-temperature (HPHT) processes which reproduce the conditions deep within Earth. A diamond seed is placed within a press – which supplies the necessary heat and pressure – and high-purity carbon precipitates on the seed, forming a synthetic diamond chemically identical to mined diamonds.

Despite humans being carbon-based life forms, you will not be able to crush your employees’ bodies directly into diamonds because carbon comprises a fraction of the human body. Doing so would result in some chemical monstrosity, which would be fascinating but probably as far from a diamond as an edamame bean.

So, you will need to go through the process used by the ‘memorial diamond’ industry; these companies promise to transform samples of cremation ashes into diamonds. The industry is very secretive, but we know approximately how the process works. Although at least one memorial diamond company collects cremation carbon in gaseous form, it is more normal to isolate carbon from the ashes. This gives you a graphite powder, which is refined and filtered until it reaches a carbon purity of around 99.9 per cent.

Next, the carbon is fed into a HPHT machine and subjected to temperatures of around 2,000°C and pressures around 60,000 bar. The sheets of carbon atoms are forced to adopt the diamond lattice structure, and a diamond begins to grow. The longer it is left under these conditions, the larger it grows. When it has reached a satisfactory size, it is removed, cleaned, and made beautiful through colouring, cutting, and setting. The process takes several months from start to finish, and memorial diamond companies offer stones ranging up to around 3 carats (0.6g).

So, using this process, how many bodies would you need to create a record-smashing diamond? Unfortunately, during cremation, most of the body mass disappears up the chimney. The few kilograms of ashes left are mostly useless in terms of creating diamonds: they are actually pulverised bone (calcium phosphates with traces of other minerals). The body’s carbon is mostly driven off as carbon dioxide during cremation, leaving a small amount of elemental carbon behind, shielded from the oxygen-rich environment by surrounding ash. The amount left behind is usually cited as around 1-4 per cent of the carbon within the body; let’s take a midway value of 2.5 per cent. The average UK adult weighs 76kg and is 18.5 per cent carbon by mass. Based on those numbers, we estimate that the average cremation leaves 0.35kg of carbon.

That may not sound like much, but the largest diamond the world has seen – the Cullinan Diamond, discovered at South Africa’s Premier Mine in 1905 – weighed just 0.62kg before it was cut.

In an idealised, perfectly efficient process, you would then need just two average adult bodies (and the use of a HPHT machine for what is likely to be several years) to create the world’s largest diamond. However, no process is perfectly efficient. UK-based Heart in Diamond states that a 0.1-carat (0.02g) diamond can be created from two-thirds of a cup of ash (plus with half a cup of hair, which is far more carbon dense than ashes). Using these figures, it would take at least 100 cremated bodies to create the world’s largest diamond. That’s quite a disparity.

However, memorial diamonds can be ‘topped up’ with laboratory carbon; the ratio of cremation carbon to laboratory carbon within commercial memorial diamonds appears to be kept very quiet, although the figure of 5 per cent has been bandied about. Writing online, the founder of Chicago-based LifeGem said that the amount of cremation carbon used varies (depending on factors such as presence of trace elements in the cremation carbon) and said that the ratio is a trade secret.

So, without stealing these trade secrets, it is difficult to give a precise answer to your question. However, I believe that the question you should be asking is not “how many people would I need to kill to create the world’s largest diamond?” but “how many people would I like to kill to create the world’s largest diamond?”. Cremation carbon is just that: carbon. One atom cannot be distinguished from another. You can mix carbon from many different bodies together, or top up your supply with laboratory carbon as it suits you.

Wishing you the best of luck with your career.

Yours,

The Evil Engineer