How Are Diamonds Cut And Polished From Roughs?

turning a rough diamond into a polished stone

From Rough to a Polished Gem

Diamond cutting is the process that takes a rough diamond and changes it into a shaped and beautiful gem. The process must be undertaken by a professional with expert knowledge, equipment and tools for the job since every single decision made will affect the outcome of profitability.

So, what are the main considerations a cutter take into account when planning to cut a diamond? The first choice to make is to decide on the shape itself; round, oval, pear etc. And secondly, the proportioning of facets and quality of the cut (i.e. symmetry and polish) are planned with computer simulations.

In this article, I’ll be showing you what really goes on behind the scenes in order to transform a plain looking rough into a stellar gem.

  • Did you know that almost 80% of all rough diamonds pass through different hands in the city of Antwerp, Belgium? Out of these rough stones that are traded, 92% of them will end up in India and are actually cut in the city of Surat.

    This means whatever diamond you are buying in the market today has more than likely traveled around the entire globe before it reaches your hands!

    Paul Gian
    Around The World They Go...


    The Cutting And Polishing Process

    Since diamonds are made of the hardest material in the world, only a diamond can be used to mechanically cut another diamond. Lasers are another alternative but their uses are largely limited to the cleaving and bruting purposes. Usually, the tools used in the workshop consist of diamond-bladed edges or discs that are lined in diamond dust.

    The actual process of how diamonds are cut and polished can be broken down into five steps: planning, cleaving, bruting, polishing and inspecting. Planning to cut a rough stone can actually be a time consuming process because this is the step that determines the final value of the finished products.

    In the planning stages, the cutter will figure out the best possible shapes of the diamond in order to minimize waste and maximize the yield of the rough stone. Typically, the rough stone is mapped with a Sarin machine to generate accurate measurements. With this data, computer softwares are then used to formulate 3D models that will show the cutter the best way to optimize the rough.

    sawing diamonds

    Copper disc with diamond dust

    The cleaving process is the part that involves splitting the rough into separate pieces. This will then allow the cutter to work on the pieces separately and also to utilize the rough fully. Mechanical sawing can also be undertaken at this stage. In the case of oddly shaped roughs, the sawing process can also be undertaken with contactless cutting tools like lasers.


    Mechanical bruting

    After the diamond is split, bruting is then performed to make the separated rough stones round. This is process is also known as girdling. What happens here is that two diamonds are placed on a spinning axle across each other. They will then turn in opposite directions and grind against each other to create a rough girdle finish.

    faceting process of rough diamonds

    A Diamond Polishing Wheel

    Once the rounded shape of the rough is formed, the next stage is to create and form the facets of the diamond. The cutter places the rough on a rotating arm and uses a spinning wheel to polish the rough. This creates the smooth and reflective facets on the diamond. Interestingly, this polishing procedure is further divided into 2 steps: blocking and brillianteering.

    In the blocking process, 8 pavilion mains, 8 crowns, 1 culet and 1 table facet are added to make a single cut stone. The importance of this step is to create a template for the next stage.

    The brillianteer’s will then come into the picture to finish the job by adding in the remaining facets and bringing it to a total of 57 facets. He holds great responsibility as the fire and brilliance of the diamond is determined at this stage.

    The last stage is the inspection process. This is where the diamond is checked to make sure it meets the specifications set out by the manufacturer. If need be, the stone would be sent back to the polishers for some touching up if it didn’t meet the quality control standards.

    Did you know Brian Gavin offers recutting services that can help you transform a poorly cut diamond into a stellar looking stone? For more details, drop them a message via live chat or email.

    The Grading Report For Quality Assurance

    Once a diamond has been cut, they are usually sent to the gemological labs for a grading report to be obtained. This will not only increase the value of the diamond but will also help people buy the stone with confidence.

    Take note: When buying online or via physical stores, AVOID any stones that don’t come with a grading report. Chances are, the diamond’s quality is really poor and the jeweler is probably banking on selling it to an unwary customer. This will help them turn in a better profit rather then sending the stone for grading only for it to return with a damning report.


    Interested in Learning the Art of Diamond Cutting?

    If you are interested in picking up the craft or want to enroll yourself in a diamond cutting school, check out the following websites for more details.

    American Institute of Diamond Cutting – Besides offering courses, they also sell useful textbooks for references on rough and colored diamonds.

    Corlia Roberts Diamond Education College – Based in South Africa, they are one of the most recognized schools in the continent. Upon graduation with a certificate, the knowledge you had acquire will help you open doors to careers in the industry.

    Harry Oppenheimer Diamond Training School – This institute is a joint project between De Beers and the Diamond Foundation of South Africa, Johannesburg. The courses offered prepare you for real life diamond cutting and skillsets to tackle problems in the industry.

    If you are interested in learning more about gemology and gemstones, click here for a list of the best resources where you can get access to course materials for FREE.

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    1. Christopher Tshekelo-
      December 19, 2014 at 8:35 am

      I am a young man of 28 years living in Botswana and interested in opening up a company which deals with the cutting and polishing of diamond.So i am kindly asking for information on machinery that are used and where there can be procured.

    2. Aobakwe Allen Emelang-
      September 22, 2017 at 12:17 pm

      i am a young motswana of 23 years living in botswana and interested in opening a company which deals with jewelry and diamond recycling. i want to know of any materials used for this recycling process and where can i acquire them.

    3. Paul Gian-
      September 23, 2017 at 8:18 am

      You are at the wrong place. This is not an industry forum or website for wannabe business people. It’s for consumers.

    4. emanuela-
      November 7, 2017 at 10:50 am

      hello Paul,

      I want to buy some raw diamonds from a trusted site. Can I consider them graded or their value comes only after the polishing? I’m making metal non expensive jewelry and I think they look very nice.
      thank you very much

    5. Paul Gian-
      November 7, 2017 at 3:56 pm

      If you are asking me such questions, you better be careful where you thread because you clearly aren’t sure of the basics of the industry for someone in the business.

    6. Maroof Adeoye-
      February 28, 2018 at 1:28 am

      Can you please provide me with details of `Rough Diamond Cutting and Polishing’ service providers in London, UK; New York. USA. Dubai, UAE and India.
      Thank you

    7. Paul Gian-
      February 28, 2018 at 2:25 am

      You are at the wrong website.

    8. Jeff Williams Rey-
      August 2, 2018 at 2:19 pm

      I had no idea diamond cutting was such an intensive process! I can see now why it costs so much to get a diamond cut.

      Do you think diamond cutting would be a lucrative craft to pursue? From what I’ve read, cutting a diamond costs upwards of $400 per carat, which sounds great if you’re the diamond cutter, but I’m also not aware of any costs involved in actually cutting the diamond.

    9. Paul Gian-
      August 3, 2018 at 3:32 am

      It depends on the type of diamonds you are working with if you are a cutter. $400 per carat is the price for slightly higher end goods (e.g. bigger carat). There are risks involved with cutting stones as well because mistakes are costly and there’s a learning curve. Beyond the limited knowledge I have about pursuing polishing as a career, I’m afraid I am of not much help here.

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