Techniques › Decoration & finishes

OPENWORKING AND SKELETONIZING

MENU

1. Introduction

Skeletonizing and openworking are two decorative techniques applied to movements horologists to give them an airy, refined and light appearance. Whether handcrafted or industrial, the working methods are the same for Openworking as for Skeletonizing. The distinction between the two terms is made with regard to the final and overall aesthetic result of the work.

2. Définition et distinction entre squelettage et ajourage

Le squelettage, comme l’ajourage, consiste à retirer une partie du métal des composants d’un mouvement horloger pour exposer les mécanismes internes tout en maintenant l’intégrité et la fonctionnalité de la pièce. Cette technique est souvent appliquée aux cadrans, aux ponts, aux platines et aux roues pour créer une structure visible du mouvement.

Squelettage : Nous distinguons le squelettage de l’ajourage par la transparence qu’il offre au travers de l’entière épaisseur du mouvement. Le résultat donne l’apparence d’un “squelette”, où les pièces essentielles sont découpées ou évidées. De plus, le squelettage concerne généralement l’ensemble de la surface du mouvement, alors qu’un ajourage peut être effectué uniquement sur une portion de celle-ci.

Figure 1

Decoration of a skeletonized main plate

Click on the thumbnail to enlarge it

Openworking: In contrast, Openworking only applies to part of the layers of a Movement. For example, the Dial and the surface of a Bridge to reveal a particular mechanism.

Figure 2

Openworked module plate

Click on the thumbnail to enlarge it

3. History

Skeletonizing has its roots in 18th-century horology, at a time when horologists (watchmakers) sought to combine both practicality and aesthetics. The technique was popularized by Swiss master horologists (watchmakers), notably those from the Geneva region, renowned for their skills in movement decoration. Skeletonizing became a way for horologists (watchmakers) to demonstrate their expertise, offering a clear view of the intricate gearing and showcasing the beauty of the movement’s internal architecture.

In the 19th century, skeletonizing became a true signature of luxury horology and reached its peak between 1950 and the quartz crisis (1974). Skeletonizing was then seen not only as a technical achievement, but also as a mark of quality and exclusivity.

4. Skeletonizing and Openworking Methods

The working methods and choice of techniques are identical for Openworking and Skeletonizing.

Design and drawing

Whatever working method is chosen (handcrafted or industrial), a work of Openworking or Skeletonizing begins with a study and a drawing of the cutouts, which must meet both aesthetic and technical criteria. Each functional element of a component must remain firmly connected to the structure, while the structure itself must retain reliable rigidity.

Handcrafted Skeletonizing

Handcrafted Skeletonizing is meticulous work carried out by hand by experienced craftsmen. It involves the careful cutting, drilling, and filing of movement components, most often using simple hand tools, such as the Piercing saw (jeweler’s saw) and files that are enough for the most dazzling creations. After generally cutting out and hollowing the components using the Piercing saw (jeweler’s saw), the craftsman “draws” their precise outlines by filing the sides. Depending on the complexity of the Skeletonizing design, filing requires significant expertise and experience specific to the technique. Artisanal Skeletonizing of a Movement generally includes all the operations of Decoration of the component (Beveling / Angling, drawing of the sides, etc.). This process can take hours, even days, for each piece, depending on its complexity. Each Movement is unique, with Skeletonizing patterns customizable according to the taste and expertise of the Horologist (watchmaker) or their client.

Semi-industrial Skeletonizing

In the case of small series or customizations, for example, the craftsman can rely on industrial or semi-industrial methods for the cutting phases in particular, before finishing his work by hand and obtaining finishes comparable to those of purely handcrafted work. Depending on the case, the nature and material of the components, their cutting can be carried out by machining (turning and/or Milling), by Stamping or by Electrical discharge machining (EDM). Electrical discharge machining (EDM) is ideal for Steel components whose cuts can be fine and complex (without mechanical stress), but it is expensive and poorly suited to large series.

Industrial Skeletonizing

In the modern watchmaking industry, skeletonizing is increasingly carried out using computer-controlled machines and laser cutting or Engraving techniques. These methods allow for greater speed and reduced production costs. However, although this approach is faster and more uniform, it can sometimes lack the authenticity and refinement found in artisanal work. The minimum diameter of a milling cutter, for example, does not allow sharp angles to be cleared. Industrial skeletonizing is commonly used in the large-scale production of watches, in lower-end ranges, and the finishing there generally also has an industrial origin (CNC beveling / angling and diamond polishing).

5. Combinations with other decorations

Skeletonizing and openworking can be combined with other forms of decoration to accentuate the visual effect. Among the most common techniques that complement skeletonizing and openworking are:

• Engraving: Engraving can be used to add fine details to the edges of openworked or skeletonized parts, creating additional light effects and artistic patterns. For example, skeletonized bridges can be engraved with floral or geometric motifs, which enriches the aesthetic appearance of the movement.
• Setting (stone/jewel setting): Setting (stone/jewel setting), which involves fixing precious stones (such as diamonds, rubies, or sapphires) onto the movement’s parts, is sometimes used in combination with skeletonizing and openworking. The stones can be placed on the edges of bridges or in the openworked cutouts, bringing an additional touch of luxury and brilliance to the watch.

6. Advantages and disadvantages

Advantages

• Aesthetics: Skeletonizing and openworking offer visually impressive finishes. They allow the engineering of the movement to be appreciated in an artistic way.
• Lightness: By removing part of the metal, these techniques help reduce the overall weight of the Movement, which can, in some cases, be beneficial for the performance of a mechanism.
• Originality: Each Skeletonizing or Openworked watch is often unique, offering a distinctive character that can appeal to collectors and enthusiasts of rare pieces.

Disadvantages

• Cost: Skeletonizing and Openworking, particularly in their handcrafted version, are lengthy and costly processes that significantly increase the price of the watch.
• Manufacturing complexity: These techniques can make production more complex, particularly during Skeletonizing, where the structure of the Movement is modified. This can affect the strength of the parts or their durability.
• Reduced strength: The addition of cutouts and perforations can weaken the structure of components, but this is now more easily offset by the strength of the materials used.

While skeletonizing exposes the mechanical beauty of watches by removing a large part of the metal, openworking focuses on the decorative aspect with more superficially cut patterns. These techniques, whether handcrafted or industrial, play a crucial role in creating unique, precise, and visually captivating watches. Their combination with techniques such as engraving or setting often elevates skeleton watches to the rank of works of art.