Technique → Decoration and finishing

OPENWORK & SKELETONISATION

Skeletonisation and openwork are two decorative techniques applied to watch movements to create an airy, refined, and lightweight appearance. Whether performed by hand or with industrial methods, the processes for openwork and skeletonisation are identical. The distinction between the two lies in the final aesthetic and the overall result.

Definition and Distinction Between Skeletonisation and Openwork

Both skeletonisation and openwork involve removing parts of the metal from watch components to expose the internal mechanisms while maintaining the piece’s structural integrity and functionality. These techniques are often applied to dials, bridges, mainplates, and wheels, showcasing the movement’s architecture.

  • Skeletonisation: Skeletonisation differs from openworking by offering full transparency through the entire thickness of the movement. The result resembles a “skeleton,” where only essential parts are cut away or hollowed. Skeletonisation usually involves the entire surface of the movement, whereas openworking might be applied only to specific sections.
  • Openwork: Openwork involves removing material only from certain layers of a movement, such as a dial or the surface of a bridge, to reveal particular mechanisms.

History

Skeletonisation has its roots in 18th-century watchmaking, a time when horologists sought to combine practicality with aesthetics. The technique was popularised by master Swiss watchmakers, particularly those from Geneva, renowned for their decorative movement expertise. Skeletonisation became a means for watchmakers to demonstrate their craftsmanship, providing a clear view of the complex mechanisms while showcasing the internal beauty of the movement’s architecture.

By the 19th century, skeletonisation had become a hallmark of luxury watchmaking and reached its zenith between 1950 and the quartz crisis (1974). It was seen not only as a technical achievement but also as a mark of quality and exclusivity.

Methods

The processes and techniques for openwork and skeletonisation are identical, differing only in their application and scope.

  • Design and Planning

Regardless of the method (artisanal or industrial), openwork or skeletonisation begins with a study and design of the cutouts. The design must meet both aesthetic and technical criteria, ensuring that every functional element remains firmly attached to the structure and that the structure maintains reliable rigidity.

  • Artisanal Skeletonisation

Artisanal skeletonisation is a meticulous process performed by skilled craftsmen. It involves cutting, drilling, and filing components by hand, often using basic tools like piercing saw and files. After cutting and hollowing components with the piercing saw, the artisan shapes the precise contours by filing the edges. Depending on the complexity of the skeletonisation design, filing requires specific expertise and extensive experience.

Artisanal skeletonisation often includes additional decorative processes, such as beveling and stretching the traits. Completing a single piece can take hours or even days, depending on its complexity. Each skeletonised movement is unique, with designs tailored to the horologist’s or client’s preferences.

  • Semi-Industrial Skeletonisation

For small series or customisations, artisans may use industrial or semi-industrial methods for initial cutting phases before completing the finishing by hand to achieve results comparable to purely artisanal work. Depending on the material and nature of the components, cutting can be done through machining (turning and/or milling), stamping, or electrical discharge machining (EDM). EDM is ideal for steel components, allowing for intricate and fine cuts without mechanical stress, though it is costly and less suited to large series.

  • Industrial Skeletonisation

In modern watchmaking, skeletonisation is increasingly carried out using CNC machines and laser cutting or engraving techniques. These methods allow for faster production and lower costs. However, while efficient and uniform, this approach may lack the authenticity and finesse of artisanal work. For instance, CNC milling cannot produce sharp angles due to tool limitations. Industrial skeletonisation is commonly used for mass production of entry-level skeleton watches, where both the skeletonisation and finishing (e.g., CNC beveling and polishing) are industrially executed.

Combinations with Other Decorative Arts

Skeletonisation and openworking are often combined with other decorative techniques to enhance their visual effect. Common complementary techniques include:

  • Engraving: Engraving adds intricate details to the edges of openworked or skeletonised pieces, creating additional light effects and artistic motifs. For example, skeletonised bridges may feature floral or geometric engravings to enrich the movement’s aesthetic.
  • Gem Setting: Gem setting involves embedding precious stones (e.g., diamonds, rubies, sapphires) into the movement’s components. Stones can be placed along the edges of bridges or within openwork cutouts, adding luxury and brilliance to the watch.

Advantages and Disadvantages

Advantages

  • Aesthetic Appeal: Skeletonisation and openwork create visually stunning finishes, showcasing the engineering of the movement in an artistic way.
  • Lightweight Design: By removing metal, these techniques reduce the movement’s overall weight, which can, in some cases, enhance the mechanism’s performance.
  • Uniqueness: Each skeletonised or openworked watch is often unique, offering a distinctive character that appeals to collectors and enthusiasts of rare timepieces.

Disadvantages

  • Cost: Skeletonisation and openwork, particularly when performed by hand, are time-consuming and expensive processes, significantly increasing a watch’s price.
  • Manufacturing Complexity: These techniques complicate production, especially in skeletonisation, where the movement’s structure is modified. This can affect the components’ strength or durability.
  • Reduced Strength: Adding cutouts and perforations can weaken the structural integrity of components, though this is increasingly offset by the strength of modern materials.

While skeletonisation reveals the mechanical beauty of watches by extensively removing metal, openwork focuses on decorative cutouts for a more subtle aesthetic effect. These techniques, whether artisanal or industrial, play a crucial role in creating unique, precise, and visually captivating timepieces. Combined with methods like engraving or gem setting, skeleton watches often achieve the status of true works of art.