HANDS
The hand is a pointer whose tip moves circularly (e.g., the minute hand), linearly, or randomly (e.g., the power reserve indicator hand) along the graduation dedicated to it, which is printed, most of the time, on the dial surface. Although they can be made from various materials, hands are generally made of metal (brass, gold, steel, aluminium…). Depending on the chosen production method, their shape, function, or design, hands can be made in one piece or in two components or more.
The hand is attached to the mobile that drives it by its cannon (tube), which is fitted (greasy fit) onto the end of the mobile pivot or the cannon of a wheel or pinion (minute hand on a cannon-pinion, hour hand on the hour wheel). The hand’s cannon, stamped or applied, carries the hand’s planchette, the end of which points to the indicated value. In some cases, the hand may have a counterweight to optimise the watch’s performance.
Various finishes can be applied to hands such as diamond-cutting, polishing, satin-finishing, sand-blasting, etc. Hands can also be partially or completely painted, or undergo colour treatments through galvanic treatements or vapour deposition (PVD, DLC, CVD, etc.). For nighttime reading, the hand can be coated with a photoluminescent material (Superluminova).
When the first mechanical clocks appeared in the late 13th century, they had neither dials nor hands. Initially, these clocks simply struck a specific hour of the day, and then, by the early 14th century, they began striking the 24 hours of a day. It was at the dawn of the 15th century that the first dials with a single hour hand appeared. Mechanical horology then progressed rapidly. The 24-hour dials were replaced by 12-hour dials, which were more readable. When Christian Huygens finalized the theory of the pendulum in the mid-17th century, the precision of clocks improved considerably, leading to the rapid appearance of minute hands.
Travel clocks and watches naturally adopted this display mode. The style and shape of the hands evolved over the centuries, often providing valuable information about the period of manufacture of the clocks or watches they powered. It was not until the early 20th century that the hand underwent its most significant evolution with the application of radioluminescent material (radium). The strong radioactivity of this material and its dangers were known as early as 1920 (the “radium girls” case). However, in Switzerland, its use was not banned until 1963. Radium was subsequently replaced by tritium, which is not radioactive to humans but has lesser luminescent properties compared to radium. It was only from 1994 with the invention of luminova that radioluminescent materials were replaced by photoluminescent materials. By definition, luminova emits light when exposed to light, like an accumulator. Its nocturnal luminescence is therefore limited in time. However, its light intensity is significant and has been steadily improving since its invention.
PENDING
An alternative to artisanal and industrial methods, particularly interesting for small series or hands with complex profiles, is to cut the hand using wire electrical discharge machining (EDM). All conductive materials are eligible for this technique, which allows for the cutting of multiple hands during the same cycle (material overlay). This technique also enables very fine and complex cuts to be made without any mechanical stress being exerted on the hand, requiring the cannon to be attached and subsequently riveted. The cut hand then undergoes finishing according to the desired result (polishing, sand-blasting, satin finishing, etc.) and can also be diamond-cut.
Subsequently, the cannon can be riveted to the hand. The hand then receives its colouring, except for hands made from gold. Depending on the desired result, colouring can be achieved through painting, electroplating, anodizing (for aluminium), or physical vapour deposition (PVD, DLC, CVD, etc.). If necessary, luminescent material is then applied to the underside of the hand. The luminescent paste fills the window created for this purpose during the initial cutting stage. Finally, dimensional and aesthetic controls are performed for each hand before it can be packaged for the final assembly of the watch.
The base material comes in the form of a strip slightly thicker than the final thickness of the hand. The first step is to form the cannon by stamping (when it is not attached). For hands intended to receive luminescent material or for skeletonized hands, the first cutout of the skeletonization is made using a screw press and cutting tools (die and punch). The next step is to cut the outer contour using the same process. The upper surface of the hand is then diamond-cut to give it its final shape (flat, rounded, faceted) and achieve a polished surface finish. Other finishing operations may follow, such as fine polishing, satin finishing, or partial or total sand-blasting. It is after this step that the cannon is riveted to the hand for hands with an attached cannon (second hands, subdial hands). Except for gold hands, the hand then receives its colouring. Depending on the desired result, colouring can be achieved through painting, electroplating, anodizing (for aluminium), or physical vapour deposition (PVD, DLC, CVD, etc.). If necessary, luminescent material is then applied to the underside of the hand. The luminescent paste fills the window created for this purpose during the initial cutting stage. Finally, dimensional and aesthetic checks are performed for each hand before it can be packaged for the final assembly of the watch.