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POLISHING

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1. Introduction

Polishing is a fundamental technique used to achieve smooth, shiny and uniform surfaces on the components of a Movement or the External parts (case, dial, hands) (Case, Bracelet / Strap, Dial, hands, etc.). This method is intended not only to improve the appearance of the parts, but also to optimise their function, resistance and durability. Whether it concerns Movement components or the Case, Polishing is an art that requires great expertise, whether carried out manually or using specialised machines.

2. Definition and purposes of Polishing

Polishing is an Abrasive finishing process aimed at eliminating surface irregularities of a Material by reducing its roughness. The main objective is to create a smooth, uniform, often shiny surface, while preserving the integrity of the Material. Polishing can be applied to a wide variety of watchmaking components to give them a refined aesthetic appearance, while contributing to their resistance to wear, corrosion and dirt.

In a timepiece, well-executed Polishing not only improves the visual appearance of the parts but also contributes to their mechanical performance, reducing friction and increasing the longevity of moving components. Moreover, polished surfaces better capture and reflect Light, creating attractive plays of Light and highlighting the details of the Movement.

3. Polishable Materials

Polishing can be performed on various Materials used in the manufacture of watch components. Each Material requires a specific approach depending on its Hardness, texture, and behavior toward Abrasives.

• Steel : One of the Materials most commonly used in horology for Cases, Bridges, Screws, and many Movement components. It lends itself well to Polishing, offering a reflective shine and good corrosion resistance.
• Gold and precious Metals : Gold, Main plate and other precious metals are often polished to achieve a bright finish. This polishing must be carried out with care to avoid damaging the fragile surface of these materials.
• Titanium: Although more difficult to polish due to its hardness, titanium can achieve a refined finish when worked with the right tools and abrasives. Some titanium alloys allow for a better polish than others. Grade 5 titanium is particularly appreciated for achieving beautiful polishes.
• Sapphire: Used for crystals or watch cases, sapphire is polished to provide perfect transparency and increased scratch resistance. Its extreme hardness makes it difficult to polish.
• Ceramics: Some luxury watches use ceramics, such as high-tech ceramics, which require complex polishing to give them a bright appearance and impact resistance.

Polishing is therefore applied to a wide range of components, from watch cases to internal components, including screws, bridges and wheels.

4. Artisanal Methods

Manual polishing is a highly precise process that requires considerable skill and meticulous attention to detail. It is often reserved for fine watchmaking pieces or delicate components, where the finish must be flawless. Horologists (watchmakers) use several tools and techniques to achieve the best result:

Depending on the material and shape of the component, the craftsman may choose from various polishing tools and methods.

• The polishing iron : Ideal for polishing angles (of a Bridge, for example). The Polishing iron is a tool that the Horologist (watchmaker) often shapes himself from a profile or a bar of soft iron, giving it the shape of a File, similar to the one used to perform the Beveling / Angling or shaping of the piece. The surface of the Polishing iron is slightly structured by fine filing of the tool. To carry out Polishing, the craftsman coats the surface of his iron with an Abrasive paste and moves it over the surface to be polished in the manner of a File.
• The tin block : A ground and very slightly structured tin block allows flat surfaces of components to be polished without deforming them. The Abrasive paste is deposited on the surface of the block. The surface to be polished is then placed directly in contact with the tin block and the component is moved with the Finger or a tool, in circular motions, until a smooth and shiny surface is obtained.
• The hand tool : An abrasive wheel of a suitable shape and size can be used on a hand tool (rotary spindle with micromotor). Such a tool is sometimes used to polish the angles of movement components. However, due to the high rotational speed of the small wheels and their relative softness, this method tends to break (round off) sharp edges and angles.
• Boxwood or gentian Wood finishes : Horologists (watchmakers) who produce high-quality artisanal watchmaking enjoy giving the final shine of a Polishing using a Boxwood tool or a carved piece of gentian bark. Old machines for Polishing pinion teeth use Boxwood wheels. The combination of fine Abrasives and such Wood species has never yet been matched by a more effective method or technology!

5. Industrial Methods

In a context of larger-scale production, particularly for series watches or components in large quantities, industrial Polishing methods are preferred. They make it possible to achieve fast and uniform results while guaranteeing consistent quality.

• Polishing using rotary brushes: This method applies to large-sized components and is exclusively intended for External parts (case, dial, hands) components (Cases and Bracelets / Straps). The Abrasive in bar form is deposited on the surface of the rotating brush. These brushes are generally made up of bristles or discs made of cotton or wool. Once the Abrasive has been deposited on the brush, the craftsman presses the surface of the component to be polished against the rotating brush.
• Vibrating drums : used for small and medium-sized parts. These devices, working by vibration, stir the parts and Abrasives (often in the form of beads or chips) in a rotating drum. The parts undergo uniform Polishing through friction with the Abrasive. The quality of such Polishing and the deformation experienced by the components make this method suited to low-cost, high production rate components.
• Diamond polishing : This technique requires tools (grinding wheels) made of Diamond or diamond-coated, and is generally performed on numerically controlled machines (machining centers or machines dedicated to Decoration). With this method, machining (e.g., Beveling / Angling) and Polishing can be combined. The surface finish obtained during machining by Diamond polishing is generally perfectly Polished.

6. Abrasives

The Abrasives play a key role in Polishing; their choice depends on the surface to be treated and the Material. Here are the main types of Abrasives used in watchmaking:

• Abrasive pastes: these are products generally based on aluminium oxide, diamond, silica or ceramics. The pastes are applied to polishing irons, tin blocks, brushes or discs, and used in artisanal and industrial polishing processes.
• Liquid abrasives: some industrial polishing operations require abrasives suspended in a liquid.
• Diamond wheels: used for diamond polishing.

The choice of abrasive depends on several factors: the hardness of the material to be polished, the type of finish desired and the method used (manual or industrial).

7. Advantages and disadvantages

Advantages:

• Aesthetics: The main advantage of polishing is the aesthetic improvement, providing a shiny, smooth finish.
• Durability : By eliminating microscopic surface irregularities, Polishing can help improve the wear and corrosion resistance of components, particularly when applied to metals such as stainless Steel or Gold.
• Friction reduction : On moving parts, high-quality Polishing reduces friction and wear, thereby contributing to greater longevity of the Movement.

Drawbacks:

• Erosion of fine details : Polishing, especially when too aggressive, can alter the fine details of a piece, such as engravings or angles. This can harm the visual appearance or the function of the piece.
• Time and cost : Manual Polishing, although of superior quality, is a lengthy and costly process. Industrial methods, while effective for mass production, cannot always achieve the same level of precision as manual Polishing.
• Risk of overheating: Polishing, especially at high speed, can generate heat, which may alter the properties of the material, notably by affecting the crystalline structure of metal alloys (see Heat treatments).

Polishing is essential for achieving parts that are both aesthetic and functional. Whether through artisanal or industrial methods, this technique offers a refined finish that highlights the beauty and complexity of watch movements, while optimising their performance and longevity.