Basic Elements › Materials › Minerals

RUBY / JEWEL (and synthetic corundum)

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2. General description

Ruby / Jewel is a variety of corundum (Al₂O₃), a crystallized aluminium oxide, characterized by a Hardness very high (9 on the Mohs scale) and excellent wear resistance. Nowadays, its presence in Movements occurs exclusively in the form of synthetic Ruby / Jewel, due to its purity, consistency and availability. The properties of synthetic rubies are identical to those of natural rubies, but they are uniform in color and do not present any Inclusion (risk of breakage).

Introduced as early as the 18th century in watch Movements, Ruby / Jewel is an essential component of bearings and friction-reduction systems, contributing decisively to the precision and longevity of watches.

3. Natural rubies and synthetic rubies

Natural Ruby / Jewel

Historically, the first rubies used in watchmaking were natural.

Characteristics:

• Variability of properties
• Natural impurities
• Limited availability

👉 Today, its use is exclusively reserved for jewelry applications (Setting (stone/jewel setting) of dials, of cases, of bracelets, etc.).

Synthetic Ruby / Jewel

Synthetic Ruby / Jewel is artificially produced from Aluminium oxide.

Main methods:

• Verneuil process (flame fusion)
• Growth by pulling (Czochralski)

Advantages:

• High purity
• Constant properties (color)
• Controlled production
• Controlled cost

👉 It is now the standard in technical applications (Movement)

4. Manufacturing of watchmaking Ruby / Jewel

Rubies intended for watchmaking are obtained through:

1. Growth of the synthetic crystal
2. Cutting into wafers
3. Precision machining (drilling, profiling)
4. Polishing of functional surfaces

These operations result in:

• perfectly calibrated holes
• extremely smooth surfaces
• precise geometries

5. Types of watchmaking rubies

Several types can be distinguished according to their function:

• Pierced Rubies (bearings) → guiding of the arbors
• Rubies with endstone → axial retention
• Impulse rubies → energy transmission (pallets, roller jewels, etc.) (cf. Distribution mechanism and Regulating organ)
• Friction reduction → rollers, etc.

6. Watchmaking applications

Ruby / Jewel is used for:

• Bearings of axles (gear trains, Balance)
• Escapement systems
• Friction reduction (fixed and rotating rollers)

It is present in practically all Movements mechanical and quartz.

7. Advantages and limitations

Advantages

• Very high resistance to wear
• Significant reduction in friction
• Stability over Time
• Non-magnetic Material
• Excellent manufacturing precision
• Exceptional durability

Limitations

• Fragility (brittle)
• Cost higher than standard Materials
• Requires precise assembly
• Sensitive to severe impacts