Diamond polishing is a precise and delicate process that requires both skill and in-depth knowledge of a diamond polisher. Polishing a diamond is a precise process that involves shaping and refining the rough stone to bring out its true beauty. The journey from a rough stone to a polished diamond involves several critical steps, each contributing to the gemstone's final brilliance and beauty.

As the oldest, still operating, diamond polishing factory in the world, we invite you to visit our factory in Amsterdam. 

Diamond Polishing Preparation and Tools

Before polishing can start, the diamond is split into two parts by a diamond cleaver. The larger piece is designated for polishing, while the smaller piece is used as a polishing tool. This tool, often a pyramid-like fragment, is essential because only a diamond can effectively polish another diamond.

The primary tools in diamond polishing include a cast iron polishing wheel, diamond powder, and olive oil. The polishing wheel, known for its durability, is essential for achieving the desired finish. Diamond powder, consisting of fine diamond grains, is used to achieve various levels of coarseness. Olive oil serves as a lubricant, ensuring the wheel operates smoothly without unpleasant odors when heated.

Polishing Wheel Preparation

The polishing wheel must be meticulously prepared before use. This involves clamping the disc between two pieces of lignum vitae wood to ensure it is level. A pumice stone is then used to smooth the surface, followed by a thorough cleaning and degreasing with ammonia and methylated spirits.

Applying Oil and Diamond Powder

Olive oil is applied to the wheel at regular intervals, typically every 5 centimeters. Diamond powder is then evenly distributed over the surface. This mixture is worked into a thick, dry paste by rubbing in small circles, creating the perfect medium for polishing.

The Polishing Process

Once the wheel is prepared, it must be "settled" by working the diamond powder and oil with a diamond held in tongs. The wheel is divided into an inner "test circle" for testing the diamond’s facets and an outer edge for actual polishing. Operating at speeds of 3000 to 3800 rotations per minute, the wheel is perfectly calibrated for the polishing process.

Experience the diamond polishing process up close with a free guided tour of our factory.

The history of diamond polishing 

Amsterdam has long been known as the Diamond Capital of the World due to its rich history and expertise in diamond cutting and polishing. The city has been at the forefront of diamond craftsmanship since the 16th century. Innovations in cutting machines and technologies have solidified Amsterdam's reputation as a leading center for transforming rough diamonds into exquisite gemstones.

Visitors can explore Amsterdam’s diamond history and craftsmanship. The city’s diamond district showcases this heritage, with Royal Coster Diamonds being one of the most renowned diamond cutting facilities and the oldest diamond polishing factory still operating. It’s possible to visit the Royal Diamond House of Amsterdam and participate in tours and workshops.

The Importance of Cut Quality

The cut of a diamond significantly influences its overall appearance and value. This process involves more than just shaping the stone; it’s about achieving the optimal interaction with light to create maximum brilliance. Read an in-depth report about grading a diamond. 

Facets and Light Performance

A diamond's facets are like tiny mirrors that reflect light within the stone. A typical round brilliant cut diamond has 57 to 58 facets, which must be precisely aligned to enhance the diamond's sparkle. The quality of these facets, their angles, dimensions, and arrangement, play a crucial role in determining the diamond’s brilliance. 

Key Aspects of Diamond Cut Quality

1. Polish: The overall quality of the diamond’s facet surfaces, evaluated for any imperfections resulting from the polishing process or wear. Polish is graded on a scale from Excellent to Poor.

2. Symmetry: The precision of the diamond's shape and the alignment of its facets. Symmetrical diamonds display consistent brightness. Poor symmetry can result in reduced light performance and diminished brilliance.

3. Cut Grade: Determined by factors such as brightness, scintillation, weight relative to diameter, girdle thickness, and the quality of facet polish. The cut grade ultimately defines the diamond’s ability to reflect light effectively.

See our polishers at work at our Diamond Factory. Book a tour and learn about the royal heritage of Royal Coster Diamonds and the craft of diamond polishing while you also learn everything you need to know about diamonds.