Section 10 (Part III): Other Materials in Watchmaking — Leather, Sapphire, Enamel, Tritium & Silicon

As technology advances, an ever-growing range of new materials continues to enter the watchmaking industry, while many traditional materials are finding renewed purpose. This section covers the remaining key materials used in fine watchmaking — from the straps on your wrist to the crystals protecting the dial, and the revolutionary silicon components now found inside the world's finest movements.

Explore timepieces that showcase the finest materials in watchmaking at Aorawa Time.

III. Other Materials

Leather Straps

This category refers primarily to the leather materials used in the manufacture of watch straps. The most widely used is cowhide, followed by sheepskin, crocodile skin, lizard skin, ostrich skin, water snake skin, Congo snake skin, and others — all of which are genuine leather. In addition to genuine leather, synthetic leather (faux leather) is also used, generally for lower-priced timepieces.

1. Silicone Rubber

Silicone rubber — commonly referred to simply as silicone — is used in the manufacture of watch straps. A strap must not only fit comfortably against the wrist, but also express a sense of refined personal style. Beyond traditional steel bracelets and leather straps, silicone straps have become the preferred choice for sports watches and dive watches, thanks to their excellent performance and distinctive character.

Silicone straps must pass rigorous testing using professional tensile testing machines and oscillation machines to verify their tensile strength, torsional resistance, and resistance to aging. Environmental compliance is a critical requirement: straps must undergo non-toxicity testing, UV resistance testing, seawater oxidation testing, and artificial perspiration oxidation testing. It should be noted that silicone straps have relatively low tear resistance and care should be taken during use.

2. Sapphire, Jade, and Gemstones

(1) Sapphire Crystal

The sapphire crystal used in watchmaking is synthetically produced from aluminum oxide (Al₂O₃). It has a hardness of 2,200 to 2,300 Vickers — second only to diamond, with a Mohs hardness of 9 — similar to natural corundum, and provides virtually complete scratch resistance on the watch surface. Sapphire crystal is typically colorless and transparent; by adding various chemical elements during production, it can be produced in a range of colors.

Coated sapphire crystal is also known as anti-reflective glass or anti-glare glass. A thin metallic compound film is applied to the surface of the sapphire crystal to alter its optical properties. Coated crystal may be single-sided or double-sided coated.

Sapphire crystal must never be polished on a concrete floor, as the floor may contain diamond or corundum powder and other abrasive particles that will scratch the crystal. Sapphire crystal can be identified using the following methods:

• Water droplet test: Place a drop of water on the crystal surface. If the droplet spreads, the material is ordinary glass; if it remains as a bead without spreading, it is sapphire. However, this method is considered low-grade.
• Fingernail scratch test: Scratch the surface with a fingernail. If there is resistance and friction, the material is ordinary glass or synthetic crystal; if the surface feels completely smooth with no resistance, it is sapphire.
• Hardness test: Measure and compare the hardness of the crystal material. This is the most accurate method, though relatively complex to perform — a diamond "thermal conductivity tester" can be used for this purpose.

(2) Mineral Crystal Glass

Commonly known as tempered glass. Hard and durable.

(3) Synthetic Crystal (Acrylic)

Commonly known as "organic glass" or acrylic.

(4) Nephrite (Jade)

Nephrite generally refers to Nephrite jade or Tremolite jade, sourced primarily from Peru, Alaska, the United States, and Myanmar. The chemical composition of Nephrite is a calcium-magnesium silicate from the amphibole group, with a Mohs hardness of 6.5 and a relative density of 2.9 to 3. Colors include white, leaf green, dark green, and blue-green, among others.

(5) Jadeite (Hard Jade)

Jadeite is a higher-quality jade than Nephrite, rarer and more valuable. Its chemical composition is an aluminum silicate from the pyroxene group, with a Mohs hardness of 6.5 to 7 and a relative density of 3.3. Colors include white, green, transparent, and semi-transparent varieties. In recent years, some Swiss watch manufacturers have incorporated jadeite into the production of jewelry watches, creating an Eastern aesthetic distinct from diamond watches.

(6) Diamond

Diamond refers to polished and cut diamond gemstones. Diamond is a natural mineral and the raw form of the gemstone; the two terms are sometimes used interchangeably. Diamond is a single crystal composed of carbon atoms, formed under conditions of extreme pressure and temperature deep within the earth — one of the most beautiful, valuable, and precious substances bestowed upon humanity by nature.

The value of a diamond is determined by four criteria: Colour, Clarity, Cut, and Carat weight (the "4Cs").

Colour: Diamonds are generally colorless and transparent. Finer distinctions include: exceptional white, superior white, white, slightly tinted white (brown/grey), light yellow-white (brown/grey), and yellow (brown/grey). Unset diamonds are graded for clarity as: LC (IF), VVS1, VVS2, VS1, VS2, SI1, SI2, and I — eight grades in total, with IF being the finest. Set diamonds are graded as: exceptional, very good, good, fair, and standard — five grades. Diamond color is graded from D (finest) downward through E, F, G, H, I, J, K, L, M, and N.

3. Enamel

Enamel is a decorative technique applied to watch cases and dials — watches featuring this technique are known as enamel watches. By craft type, enamel is divided into three categories: cloisonné enamel (Jing Tai Lan / Champlové), filled enamel (press-fired), and miniature painted enamel.

4. Tritium — A New Luminescent Material

Tritium (also known as gaseous tritium light sources, or GTLS) is a new type of light source — described as an "atomic eternal lamp." It is an environmentally friendly, high-technology material with an exceptionally long luminescence duration, capable of glowing continuously for 24 hours and with a service life of 10 years or more (some sources cite up to 25 years). Tritium is a rare element, present in only trace amounts in nature, and carries no radiation hazard.

5. Silicon — A New Material for Watchmaking

Silicon is one of the most important materials in the IT industry — and in recent years, it has been introduced into watchmaking.

• (1) Beginning in 2003, silicon hairsprings, silicon balance wheels, silicon gear wheels, silicon escapement mechanisms, and silicon movement plates began to appear. These components are produced through photolithography and etching processes — a new manufacturing technology capable of producing miniature, complex, and highly precise silicon components with ease.
• (2) Silicon hairsprings offer the best anti-magnetic and anti-rust performance of any hairspring material — surpassing all previously available high-quality hairsprings.
• (3) Silicon components require no lubrication.
• (4) This represents a "collective cloning" new technology and new process — high efficiency, low cost. Could it herald a new global revolution in watchmaking? Today, Patek Philippe, Rolex, the Swatch Group, and Ulysse Nardin, among many other brands, have begun using silicon hairsprings, silicon escapement wheels, and silicon pallet forks.

From sapphire crystals to silicon escapements, the materials of fine watchmaking are a story of relentless innovation. Discover timepieces that embody this pursuit of perfection at Aorawa Time.