In preparation for cleaving, the stone is set on top of a tapered wooden stick with a cement head. The cement used in diamond cleaving is composed of the following ingredients: shellac, and resin, and some other secret ingredients. When the cement head is gently heated it becomes soft and sticky but then becomes rock hard when cool.

Another diamond with a sharp edge (also set in a stick) is then used to make a V shaped groove in the stone that’s going to be cleaved.

The groove has to be made exact on the growth plane or in the direction of the octahedron. It is basically the she principle as splitting wood for your fireplace, only a little costlier if you get it wrong!

Once the groove is deep and sharp a blunt metal blade is inserted into the groove, it should fit about halfway in. A short sharp hit with a metal hammer or stick will then split the stone. Today a lot of cleavers use wooden hammers for cleaving but neither my brother nor I ever used one, and touch wood, have never had any accidents.

Some weeks before, my brother Joseph sought advice from the old cleaver A Asscher and...the rascal (that was me). Is it actually possible to cleave a stone that weighs over three thousand carats?  Are human hands actually capable of such a feat?

The factory when it reopened in 1945 after the war.

“Are human hands

actually capable of

such a feat”

Table and tools that were made specially for the job.

Some five or six years before they had some experience in cleaving the ‘Excelsior’, a rough diamond weighing more than nine hundred carat. This stone belonged for the biggest part to the London Rough Syndicate, today known as the Diamond Trading Company (part of DeBeers) The Asschers also had a substantial interest in the stone.

They sought comparisons with the large stones. ‘The Jonker’ a stone belonging to H Winston in the United States weighed over seven hundred carats, the “Woyie’ belonged to Chester Beaty. manufactured by Briefel and Lemur in London also weighed in at seven hundred carats.

Well, the Excelsior had kept the old man Asscher and Joseph busy for weeks, it was murder! The first groove took nearly two days to cut. On a Wednesday afternoon,I was free from the school and I witnessed the first attempt to cleave the stone. It split beautifully in two, and both surfaces were as smooth as a mirror, the pieces were then sent to London, there to be processed further.

Curiosity:

All the polished stones (from the Excelsior) became blue and white, as beautiful as can be, but two pear shapes, each weighing twenty-five carats, turned brown, in my fifty year career I have rarely witnessed such a thing.

Back to business, Joseph gave me the following tasks.

  1. Create and manufacture an extra sturdy cleaving table.
  2. Construct a cleavers box with a sliding side wall, which would drop this large stone to the required level so the sharp pieces of rough used to make the groove, would be at the right height.
  3. Fabricate cleaving sticks to hold this massive stone in different sizes.

Of course at the same time, all of the other polishing tools had to be manufactured and given the unusual size of the stone it gave the polishing expert A Asscher the necessary headaches.

Firstly the polishing disc had to be four times the normal size and four times as heavy, discs usually run with a spindle under and above and are kept in place with two blocks of hardwood. In those days nobody had found a way to make the axle run smooth in anything else but hardwood, but with such a large heavy disk, imagine if the wood were to split. It would send the disk flying across the workshop, tools, diamonds and all!

In the machine room was an old-fashioned fitter, Master Chardon. To him go all the honours for creating a construction in phosphorus bronze with at its centre, a spindle on which the disk ran as smoothly as in the hardwood. And then there were the polishing clamps and the large cups to hold the stones etc.

A rough diamond of a hundred carats was not a rarity, and set in a cup made of copper filled with solder, that was quite a task to handle because of the weight. After cleaving (the Cullinan), a piece of diamond weighing more than a thousand carats would have to be fitted into such a cup filled with lead. This would then be fitted and lowered onto the polishing disk countless times. A rough estimate put the total weight at about fifteen pounds. Under no circumstances could one drop the clamp with the stone onto the polishing disk, this would have meant disaster! A lifting construction was made with a counterbalance weight, but, in the end not used. Henri Koe ably assisted by his brother Salomon, handled the clamps as if they were of feathers. Within six weeks all preparations were finished.

The studio specially installed for the polishing of the Cullinan.
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