Diamond Cutting And Polishing (2022)

Diamond cutting and polishing transforms a lackluster rough stone into a scintillating faceted beautiful gemstone. At the same time, the process helps in learning the internal structure of the diamond. Also, we are able to analyze the inclusions trapped inside the diamond.

Rough Diamond To Polished Diamond

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The polishing technique is intriguing to say the least. Let us understand the essence of diamond cutting and polishing and take a look at the tools of this trade.

Humans did not acquire the art of cutting and polishing diamonds for many thousands of years after the stones were initially discovered. Yet, quality diamond roughs were treasured in their crystal form at that time too. Quality crystals were cherished as objects of beauty. Roman noblemen studded beautiful octahedral crystals into their rings.

In addition, people also understood the usefulness of diamonds as engraving tools. They could grind, engrave and cut other mineral crystals because of the diamond’s innate hardness. As such, inferior quality diamonds were crushed and used as abrasives. All the same, finer diamond crystals were enjoyed in their rough state.

Rough Diamonds

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Fast forward to present day and we are used to seeing diamonds everywhere in their cut and polished state.

Diamond cutting and polishing is the transforming technology that has made these scintillant gemstones possible.

What does a modern diamond polishing setup look like?

And this is what a modern polishing setup looks like.

Modern Diamond Polishing Setup

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You have this wheel called a scafe. It is fabricated out of cast iron or steel. A multitude of tiny diamond particles are ingrained into this wheel. The diamond to be polished is held in an instrument called the tang.

The scafe rotates at a high speed. The diamond is held and pressed against the rotating scafe with the help of the tang. As a result, the diamond gets exfoliated and you get a shining mirror finish.

The technology has remained constant for centuries. And human beings have been using it since eons. We can de-clutter the process somewhat by breaking it into intermediate steps. They are as follows.

Planning & Marking, Cleaving or Sawing, Bruting, Polishing, and Final Inspection.

Planning: At the planning stage, experts assess the rough diamond using a state of the art anti-vibration technology and under very high magnification. They do this to determine its classification and possible final yield. The diamond is further analyzed by harnessing 3D rough planning computer simulation technology. In this manner, experts optimize the polished yield that can be extracted from the rough.

Marking the Rough Diamond. The decision as to whether or not to divide the diamond crystal is made by an individual called the marker. This is a crucial step in the diamond cutting and polishing process because it represents the major decision on how to manufacture a given piece of diamond rough. The marking of a stone comes only after considerable evaluation, as any error made at this stage (of the manufacturing process) is irreversible.

Diamond Marking

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The marker examines the rough diamond with a loupe and, frequently, measures the dimensions of the diamond with a gauge. He then marks a black line on the diamond crystal’s surface. In the next step of the manufacturing process, the crystal will be either sawn or cleaved along this line.

What is diamond cleaving?

Many a time, when you try to break a diamond it will shatter into hundreds of infinitesimal pieces. But, this need not happen if you understand the structure of the diamond crystal. Also, you need to be very careful and precise.

You can exploit the diamond’s crystal structure to cleave it into a desired shape. You can do this by regulating the break. While this skill of controlled breaking was known to men much earlier, the art of polishing came much later.

Octahedral Diamond Crystal

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Our understanding is that the diamond is an octahedral crystal. It will break apart cleanly in its one one one octahedral crystal plane. This plane is parallel to an octahedral crystal face. Planes that are parallel to octahedral faces are planes of weakness within the crystal structure. The diamond can be split almost perfectly along these planes.

Octahedral Rough Diamond Crystal

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[When we use the term “one one one octahedral crystal plane”, the numbers “one one one” are nothing but Miller Indices. Watch the following video if you want to understand what are Miller Indices?]

You will have to scratch a tiny notch or a kerf on the surface of the diamond. The intention is that we insert a little blade-like wedge into the notch and smack it with a little hammer.

Cleaving Of Diamond

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The notch will propagate along the cleavage plane and the diamond will break cleanly if the kerf and orientation of the diamond is planned carefully in conjunction with the diamond crystal structure.

It is difficult for us to visualise the cleavage plane of a diamond. This is because most of us rarely come across a rough diamond in everyday life. And we never get the opportunity of breaking one.

Perforated Paper

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However, what we do come across is pre-perforated sheets of paper. You have seen kitchen tissue rolls or stamp paper sheets which are pre-perforated. You can easily tear these paper cleanly along these perforated lines. Cleavage planes in a diamond crystal are akin to these perforated lines. The gem breaks cleanly along these planes if done by a knowledgeable person.

Diamond Cleaves Perfectly On Its {1 1 1}Plane, Which is Parallel To Its Octahedral Crystal Face

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Let us take a look at an octahedron diamond crystal. It shows an edge of an octahedron and the other edges are all one one one octahedral planes. And these ought to be planes of weakness inside the diamond. We should be able to cleave it along these planes.

Incidence Of a Plane of Weakness

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See the plane on the right upper edge. The dotted red shows the incidence of a plane of weakness.

And here is what the crystal structure would look like under high magnification. You can almost notice the gap in the crystal structure. Furthermore, this gap is a recurring feature in every layer of atoms. Other planes of weaknesses also exist along which we could cleave the diamond. We realize that the diamond crystal lattice controls the geometry.

Diamond Cleavage Structure (See the gap in the crystal structure marked by red dotted line.)

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What is sawing of diamond?

Sawing is another method used to shape the rough before polishing facets. Earlier, the diamond sawing tool was a simple frame holding a wire. The petite little wire was besmeared with diamond powder & oil to give it some grit.

Bow Wire Saw

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You too needed determination, patience and grit to saw a diamond. It was a time intensive as well as labour intensive process till the time the motorized diamond saw was invented. This technique has its own innate advantages.

It lets you carve up the rough along other planes besides the one one one cleavage planes. This method of working allows you to design the diamond along cubic planes, the one zero zero planes as well as the one one zero plane. So you can play with more freedom while dividing up a large piece of rough.

If you remember our earlier discussion, in the cleaving technique, you are bridled with the one one one cleavage plane.

So if you have the choice to either cleave or saw, it gives you a lot of room to manoeuvre. You can let your creativity run loose. You can design more shapes. You can make optimum utilization of available rough with less wastage.

But, as mentioned earlier, the process used to be very labour and time intensive. That is, until the invention of the motorized diamond saw.

Here is a Video Showing You The Working Of a Motorized Diamond Saw

In place of the diamond embedded wire tool, we have a wheel that rotates continuously spurred by a motor. The rotating disc is made up of copper or bronze and it has little tiny diamond particles in it. You can saw the diamond on this wheel in predominant directions.This machine saves you a lot of manual labour and time.

Motorized Diamond Sawing Set Up

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You can see an octahedral diamond crystal being sawed along the cube plane. It is also known as the four point or sawing plane and the image on the right shows that.

You can also saw diamonds on the two-point plane which is actually a one one zero or dodecahedral plane. If you try to deviate from these planes, it does not work out. The saw will be badly damaged before you can saw even a little bit.

So you are restricted to these crystallographic orientations inside the underlying framework of the diamond crystal itself.

What is laser cutting or laser sawing of diamond?

Laser cutting of diamond involves use of extremely thin but very intense laser beams to cut out desired shapes from the diamond rough.

Diamond cutting and polishing doubtlessly came off age with the advent of the laser cutting technique in the 1970s. It is being increasingly used in the industry. This methodology gives manifold advantages.

It is faster and relatively easier to control. But much more than that, you can not only cut planes into the diamond, but also, you can actually shape the diamond using the laser.

Besides invention of laser cutting technology, additional innovations accorded precise computer control of diamond movement. The diamond could now be moved back and forth with exactness while cutting.

Another very interesting advancement in this technique was developed recently. It is the use of the laser beam inside an extremely fine water jet. The laser is condensed and fed into a water jet. The thin stream of water behaves akin to a fibre optic cable.

The water-jet can be as thin as the width of a human hair. The laser beam contained in the gossamer stream of water is very sharp and focussed. When it hits the diamond it starts ablating the diamond material. This method gives you a lot more flexibility in shaping the diamond.

You can not only saw the diamond but also shape it up for final polishing under the laser itself. The next step of bruting can be bypassed completely.

This reduces the number of steps between cutting and polishing involved in the traditional method. Laser cutting is thus a nifty technique. Further, it can be used in more imaginative ventures like carving diamonds into incredible three-dimensional shapes.

Let us summarise what we have seen till now. We take a rough diamond. We either cleave it or saw it to give it the desired initial rudimentary shape.

What do you mean by diamond bruting?

Once you have cut or sawed the rough diamond into the desired rudimentary shape, the next stepin the diamond cutting and polishing process is bruting. By bruting, we are able to impart the outline of the diamond’s girdle. Traditionally, this has been done by turning a diamond on a lathe or against another diamond. The diamond grinds away until we have the round outline of the girdle.

Bruting works not only for sculpting round brilliants. Rather, the advent of computer controlled bruting technology has facilitated fashioning of diamonds into fancy shapes like a cushion, marquis or square.

It is pertinent to point out that bruting produces diamond dust or diamond shavings.

What do they do with diamond shavings?

The diamond shavings can be put into two types of uses based on their size and quality.

If they are sufficiently large in size and of gemstone quality, they are used in adorning jewelry as diamond accents and halos.

On the other hand, if they are too small or of poor quality, they are collected and put to use as grit for sawing or polishing more diamonds.

We move on to polishing, a process that renders the diamonds into the sparkly gemstones we love so much.

You will be quite surprised to know that humans have been polishing diamonds since the middle ages. And it is not surprising at all that the origin of this craft is not well recorded. After all, it is a precious skill and must have been a zealously guarded trade secret.

But we can be pretty sure that polishing was prevalent in India since the early 13th century. In fact, certain examples of jewelry even from the late 12th century show that some artisans in this region had started acquiring the art of diamond polishing.

The technology traveled from India to Europe with diamond trading merchants. By the 1300s, crafters were polishing diamonds in Venice too. And from thereon it spread all around.

But, the technique was documented in detail by a sculptor & goldsmith named Cellini in Florence in the year 1568. As such, we have a painstaking description of the methods that were being used in 1568.

Here is a picture of what was essentially outlined by cellini. What you are seeing is an illustration of 16th century polishing. And it is quite fascinating to see its similarity to the methods of today.

Ancient Diamond Polishing

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In the picture you can see a fast-rotating polishing scafe. It is being driven by a belt that is attached to a big wheel. The wheel is driven by hand. The scafe is rotating very fast.

The rotating speed would be near three thousand rpm just like it happens today. A person at the left is holding on to a tang that’s holding a diamond. Most of what we see here is comparable to what diamond polishers do today.

The scafe is embedded with diamond particles. The diamond is being held in a dop and tang and it is being pressed against this rotating scafe for polishing. So the equipment and motions are much like what they are today.

The diamond is held firmly in the tang by means of cement, solder or wax. It could also be held in place with a jaw-like mechanical contraption.

In either case, it is very important that the diamond being held and polished can be moved and maneuvered. By doing so, you should be able to adjust its orientation.

This is because the orientation of the diamond is crucial in two respects. Firstly it aligns the facet correctly on the face of the diamond. Secondly, it amends the orientation of the diamond in relation to the rotating scafe. So a slew of machines and mechanics remain unchanged. We still also do this by hand.

But in the 1970s, computer control of diamond maneuverability came along with the laser cutting technology. Armed with this ability we could invent automatic polishing machines.

Today, such machines are much more advanced. They can detect the polishing direction. Accordingly they can turn the diamond in the precise soft polishing direction.

Synova is a Swiss-based provider of advanced laser cutting systems for diamonds. It has announced an ingenious automatic cutting & shaping solution for Diamond Manufacturers. They are affirming that the system can start from rough and deliver a completely shaped diamond with 57 facets in a single process.

The system named as “DaVinci” combines several manufacturing processes into one machine. It thus reduces diamond production time appreciably. It also reduces the number of processes from rough to the final finishing step.

It is touted to be the first automated laser full faceting solution for round brilliants on the market. It will revolutionize the diamond manufacturing industry because the system covers the complete Rough-to-Polish process. The system renders several cost, skill & labor-intensive steps in the polishing phase (such as crown and pavilion blocking, girdle bruting or recurrent quality checks) redundant.

Consequently, manufacturing capacities can be augmented or adapted based on seasonal and locational demands. It increases the quantum of polished yield. It spruces up the stone symmetry with higher machine accuracies. Furthermore, value is added by allowing reuse of diamond chips that are cut off from rough stones during laser cutting.

The heart of the DaVinci system is Synova’s DCS 50, a highly accurate and well-established laser machine based on the advanced Laser MicroJet technology. The 5-axis CNC machine integrates Synova’s patented breakthrough detection that recognizes when a cut is finished and automatically initiates facet changing.

The water jet guided Laser MicroJet cools the diamond surface during laser ablation and significantly reduces the risk of rough diamond cracking, especially with stress stones. The water jet maintains the laser’s focus creating a cylindrical laser beam resulting in perfectly parallel walls and tight kerf widths.

If the diamond is not in this optimum soft polishing direction, the diamond cannot be polished. You will be wasting your efforts, energy and time. On top of that you might end up damaging the expensive scafe wheel. The automatic polishing machines are able to find that soft polishing direction by themselves.

You will also find it intriguing that diamond polishing involves something very different when compared to polishing other materials.

For now, let us talk a little about polishing some other material and not diamonds.

Let us consider the polishing work of gemstone topaz. It would entail rubbing our work-piece against some kind of hard abrasive material. As a result, our work-piece whittles away. Consequently, you have little breakaway particles of topaz that are broken off and washed away.

Polishing by abrasion may also involve three body wear. In this case we have a substrate that might be something soft like a cloth or a metal disc that’s not very hard. And along with the substrate, we have to use a polishing paste or a slurry which contains tiny hard abrasive particles in it. The abrasives wear away the work-piece.

Tiny bits of topaz are shed in the process and your work-piece keeps becoming smoother. You will incrementally move to finer and finer abrasive particles. The scratches or cavities on the topaz work-piece become smaller and smaller. Ultimately, the work-piece sparkles with a gleaming mirror finish.

We would be pardoned to think that diamond polishing would work in the same way yielding diamond particles powder as a by-product in the process.

But, we know that diamond is the hardest natural substance known to men. And we have here a diagram of Mohs scale of hardness.

We have different minerals ranked in order of hardness and diamond is number ten. We can see that it is harder than corundum which is the next hardest thing at number nine.

Mohs Hardness Scale

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Yet, you should further plot this on a different kind of scale of indentation hardness like the Vickers hardness test. When you do this, you notice that diamond is not just one number harder. It is several times harder than corundum.

Vickers Hardness vs. Mohs Hardness

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So diamond itself is the only material that can chafe a diamond. As such the rotating scafe is embedded with tiny particles of diamond grit. Further, you might hold the belief the diamond is being scratched away. The ultra thin lines in the polished facet of the diamond seem to reinforce this idea.

However, the reality is something different. To understand this, examine the purported scratch lines under high magnification. And, you will realize that the scratch lines are much too thin. Their thickness can be measured in nanometers. On the other hand the diamond grit particles are much too large. Their thickness is more than a micron.

This establishes that the scratches in the polished facet of the diamond are not from the diamond grit. What transpires here is more enigmatic.

And the mystery deepens when you discover that what is deposited on the rotating scafe are not diamond particles or diamond dust. Instead, what you see deposited on the scafe is just carbon. It is not diamond anymore. The material being worn away has undergone a phase transition. It has metamorphosed into something like graphite or even amorphous carbon.

This goes on to show that the polishing process is much more perplexing than what your intuition might tell you.

Scientists are still actively researching and trying to solve this puzzle as to how a diamond allows itself to be polished.

We need to understand these goings-on not only out of curiosity. But the polishing process is also pivotal in many technological applications.

High efficiency lasers need diamond facets polished with unerring accuracy. Similarly optical devices and diamond lenses need precisely polished diamond facets. Furthermore, you might want to use diamonds in watches and timepieces.

Hence, we should be able to polish really excellent surfaces on diamonds. Consequently, diamond polishing continues to be an active area of research. It is fascinating that we still don’t fully understand the process in spite of all the advancement in computerized technology.

The polishing scafe rotates very quickly at around 2400 to 3000 revolutions per minute. This scafe may be infused with diamond dust rubbed into it with oil. Or else, the scafe might be electrochemically bonded with diamond powder. When the roughage of the diamond coating wears out with continued use, the scafe is changed with a fresh one. The one that is replaced is sent to be re-coated with diamond dust.

For the purpose of polishing, the diamond is held in a tool setup known as the dop and tang. It can become incredibly hot with friction. You should be able to hold the diamond securely and be able to maneuver & reposition it very accurately without burning your fingers.

One more startling thing is that the direction of polishing is vital. This is because the diamond has hard directions as well as soft directions. It has a grain akin to the grain in a piece of wood. If you cut the wood with the grain, it requires little effort. But if you try to cut it against the grain, it is very difficult to cut, requires a lot more energy and it causes a much higher wear and tear to the cutting tools.

We bring the above analogy and terminology to diamond polishing. Shall we say, the idea is to polish the diamond with the grain. It alludes to polishing the diamond along its softer surface direction.

We spoke above about the tool setup of dop and tang. The diamond is held firmly in the jaw like structure of dop. The dop can be rotated along its vertical axis. It helps the polisher to find the optimal soft direction for polishing the facet.

This aspect is of great consequence in the process of polishing. It brings to us this idea of where the anisotropy or the grain within the diamond exists.

An expert in diamond cutting and polishing has studied the crystallographic directions within the diamond. He understands the geometry and the sort of molecular bonds in the crystal lattice. He knows precisely the direction in which a diamond can be polished with relative ease. He holds the diamond in the tang and can rotate it about its axis to find the soft grain, the soft polishing direction.

But if he tried to polish this facet in other directions, it would create many problems. First of all, the diamond will not be properly polished. Secondly, whatever polishing occurs would be very slow and pain-staking. Thirdly, it could badly damage the surface of the scafe wheel.

Now, if he rotates the diamond a little bit, he would start to polish better. Finally, when the direction is just the right soft polishing direction, he can actually hear & feel the difference. The friction between the facet and the scafe increases and the wear rate improves immediately. The diamond starts polishing satisfyingly.

Another factor influencing the quality and speed of diamond polishing is the rotational speed of the scafe disc. Experience has taught us that 3000 rpm is the optimum speed which yields the best polishing.

Increasing the speed still further causes overheating of both the diamond and the scafe disc. This may cause cracking of the precious diamond or damage of the expensive scafe disc.

On the other hand slower speeds make for inefficient polishing and further if the speed slows beyond a certain point, the polishing stops completely even though the disc is still rotating. You need to have a fast enough speed to trigger the mysterious process of diamond polishing.

Yet another factor considerably influencing polishing rate is the quantum of pressure being applied on the diamond. To make use of this phenomenon, at times polishers weigh down the diamond using a little sandbag to create additional pressure. This results in higher wear rates. As such, you can do the polishing at a faster pace.

On the flipside, this generates much greater frictional heat. The quality of polishing is affected. Moreover, the diamond can actually become red hot and crack with the intense heat.

Conversely, polishers polishing colored diamonds (particularly green diamonds) reduce the pressure on the diamond. They do this by attaching a little counterweight to the other edge of the tang. The dangling weight takes the pressure off the diamond chafing on the scafe.

If the workpiece happens to be a green diamond, the polisher has to be extraordinarily careful. If the temperature of this green diamond happens to go beyond 400 to 500 degrees celsius, the diamond loses color and value. It might even start turning brown and dramatically reduce in value.

What is triboluminescence

One more amazing spectacle that occurs during diamond polishing is a phenomenon known as triboluminescence. As the diamond is being worn away and getting polished, it sometimes lights up. The activity is not fully understood. But it is thought that an electric field might be getting created and the diamond might be behaving like a light emitting diode.


More About Diamonds:

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Diamond Cut GradingDiamond Rings Cut
Diamonds InclusionsSeven Tips To Make Your Diamond Look Larger
Repurpose your DiamondsType II Diamonds
Detecting HPHT Diamond MeleeKrupp Diamond
Diamond Clarity and VS1 Clarity Diamonds

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