POLISHING

Polishing is a fundamental technique used to achieve smooth, shiny, and uniform surfaces on watch components, including movement parts and external elements such as cases, bracelets, dials, and hands. This method not only enhances the appearance of the pieces but also optimises their functionality, resistance, and durability. Whether applied to movement components or cases, polishing is an art requiring great expertise, performed either manually or with specialised machinery.

Definition and Objectives of Polishing

Polishing is an abrasive finishing process aimed at eliminating surface irregularities on a material by reducing its roughness. The primary goal is to create a smooth, uniform, often glossy surface while preserving the integrity of the material. It is widely applied to horological components, ensuring a refined aesthetic while improving resistance to wear, corrosion, and dirt.

In a timepiece, well-executed polishing not only enhances the visual appeal of components but also improves their mechanical performance by reducing friction and increasing the longevity of moving parts. Moreover, polished surfaces better capture and reflect light, creating attractive light effects and highlighting the details of the movement.

Polishable Materials

Polishing can be performed on various materials used in watch components. Each material requires a specific approach depending on its hardness, texture, and reaction to abrasives.

Stainless Steel: A commonly used material in watchmaking for cases, bridges, and screws. It polishes well, achieving a reflective shine and excellent corrosion resistance.
Gold and Precious Metals: Gold, platinum, and other precious metals are often polished to a bright finish. This requires care to avoid damaging their softer surfaces.
Titanium: Though more challenging to polish due to its hardness, titanium can achieve a refined finish with appropriate tools and abrasives. Grade 5 titanium is particularly appreciated for its excellent polishability.
Sapphire: Used in watch crystals and cases, sapphire is polished to achieve perfect transparency and high scratch resistance, although its extreme hardness makes the process demanding.
Ceramic: High-tech ceramics used in luxury watches require complex polishing techniques to achieve their shiny appearance and impact resistance.

Polishing is applied to a wide range of components, from cases to internal parts such as screws, bridges, and wheels.

Artisanal and Industrial Methods

Artisanal Methods

Manual polishing is a highly precise process requiring significant skill and meticulous attention to detail. It is often reserved for high-end horology or delicate components where flawless finishing is essential. Horologists use several tools and techniques to achieve optimal results:

Hand Polishing: Depending on the material and shape of the component, the artisan selects appropriate tools and methods.
Polishing Iron: Ideal for edges (e.g., of a bridge). The polishing iron, often shaped by the horologist, consists of a mild steel profile or bar given the shape of a file. The tool’s surface is slightly textured with fine filing. To polish, abrasive paste is applied to the iron, which is then moved over the surface like a file.
Tin Block: A flattened and slightly textured tin block is used to polish flat surfaces without deforming them. Abrasive paste is applied to the block’s surface, and the component is moved in circular motions by hand or with a tool until smooth and shiny.
Hand Tool with Abrasive Wheel: An abrasive wheel of the appropriate shape and size can be used on a handheld rotary tool (e.g., micromotor). This method is sometimes employed for polishing component edges but risks rounding sharp angles due to the wheel’s flexibility and high rotation speed.
Boxwood or Gentian Wood Finishing: Craftsmen in high-quality artisanal horology often achieve the final polish using boxwood or gentian bark tools. Older machines for polishing pinion teeth also used boxwood wheels. The combination of fine abrasives with these wood types remains unmatched for effectiveness.

Industrial Methods

In large-scale production, particularly for mass-produced watches or components, industrial polishing methods are preferred. These methods deliver fast and consistent results while maintaining quality.

Rotary Brush Polishing: This technique is used for large components, primarily for cases and bracelets. Abrasive compounds in block form are applied to rotating brushes made of cotton or wool. The artisan presses the surface of the component against the rotating brush to achieve a polished finish.
Vibratory Tumblers: Used for small and medium-sized parts, vibratory tumblers agitate the components and abrasives (usually in the form of balls or chips) in a rotating drum. Friction between the parts and abrasives results in uniform polishing. This method is typically used for inexpensive, mass-produced components.
Diamond Polishing: This technique uses diamond-tipped or diamond-coated tools and is usually performed on CNC machines or specialised decoration equipment. It allows for a combination of machining (e.g., beveling) and polishing, producing perfectly polished surfaces directly during machining.

Abrasives Used

Abrasives are essential in polishing, with their selection depending on the material and surface to be treated. The main types of abrasives used in watchmaking include:

Abrasive Pastes: Typically made from aluminium oxide, diamond, silica, or ceramic. These pastes are applied to polishing irons, tin blocks, brushes, or discs for both artisanal and industrial processes.
Liquid Abrasives: Certain industrial polishing operations use abrasives suspended in liquids.
Diamond Wheels: Used for diamond polishing operations.

The choice of abrasive depends on several factors: the hardness of the material, the desired finish, and the chosen method (manual or industrial).

Advantages and Disadvantages of Polishing

Advantages:

Aesthetic Appeal: Polishing enhances the visual appearance of components, giving them a smooth and shiny finish.
Durability: By removing microscopic irregularities, polishing improves wear and corrosion resistance, particularly for materials like stainless steel or gold.
Reduced Friction: High-quality polishing on moving parts reduces friction and wear, increasing the movement’s longevity.

Disadvantages:

Loss of Fine Details: Excessive or aggressive polishing can erode fine details such as engravings or edges, potentially affecting the piece’s appearance or functionality.
Time and Cost: Manual polishing, though superior in quality, is time-consuming and expensive. Industrial methods, while efficient for mass production, cannot always achieve the same level of precision.
Heat Risks: Polishing at high speeds generates heat, which can alter the material’s properties, such as affecting the crystalline structure of metal alloys (see thermal treatments).

Polishing is essential for creating components that are both visually stunning and functionally optimal. Whether performed through artisanal or industrial methods, this technique delivers the refined finishing that enhances the beauty and complexity of watch movements while optimising their performance and longevity.