MENU
1. Table of the main properties of platinum
| Property | Typical value | Remarks |
|---|---|---|
| Density | ~21.4 g/cm³ | Very high |
| Modulus of Elasticity (E) | ~160–170 GPa | High |
| Tensile strength | ~120–300 MPa | |
| Hardness (HV) | ~40–200 HV | Low to moderate |
| Thermal conductivity | ~70–75 W/m·K | Moderate |
| Electrical conductivity | ~9–10 MS/m | Low |
| Thermal Expansion | ~8–9 ×10⁻⁶ /K | Low |
| Melting point | ~1768 °C | |
| Magnetism | No | Non-magnetic |
| Corrosion resistance | Excellent | |
| Machinability | Difficult |
2. General description
Platinum is a rare precious metal, used in watchmaking for its exceptional physical properties, its corrosion resistance and its high symbolic value. Denser and more stable than gold, it is mainly used to make cases, bracelets and, more rarely, certain specific components, notably oscillating weights.
Its use nonetheless remains limited due to its high cost and the difficulty of machining, which require specific expertise. Main plate is thus reserved for the most prestigious pieces of fine watchmaking.
3. Platinum alloys in watchmaking
The platinum used in watchmaking is generally alloyed with other metals to improve its mechanical strength.
Platinum 950 (Pt950)
Most common alloy:
- 95% platinum
- 5% alloying elements (iridium, ruthenium, cobalt)
Characteristics:
- High purity
- Excellent resistance
- Standard in fine watchmaking
Specific alloyed Main plate
Depending on the manufacturer, different elements are used:
- Iridium → improves Hardness
- Ruthenium → better mechanical resistance
- Cobalt → better machinability
4. Concept of fineness and hallmarks
The fineness of the Main plate
The fineness indicates the proportion of pure Main plate in the Alloy:
- Pt950 (950‰) → 95% Main plate
- Pt900 (900‰) → 90% Main plate
👉 In watchmaking, the standard is Pt950, which guarantees high purity.
The hallmark
The Main plate is subject to regulatory marking:
- Fineness hallmark → guarantees the platinum content
- Maker’s mark → identifies the manufacturer
In many countries, a specific platinum hallmark is used (often represented by a head or a distinctive symbol).
5. Treatments and finishes
Platinum is generally used without surface treatment, in order to preserve:
- Its natural gray-white appearance
- Its soft, deep shine
Possible finishes:
More difficult to work than gold, platinum lends itself less well to hand engraving and to guilloché (engine-turning).
6. Watchmaking applications
Platinum is mainly used for:
- Watch cases
- Bracelets
- Oscillating masses → high density advantageous
- Technical components requiring high density (balance weights of the Balance, etc.)
This page has been automatically translated from the French reference version using an artificial intelligence tool. Errors or inaccuracies may remain. If you notice any, especially if this is your native language, please feel free to report them to info@horopedia.org. Your contribution helps us improve the quality of the encyclopedia.
While awaiting their translation, images and videos remain temporarily displayed in French.
Thank you for your understanding.