Table of Contents

Stainless Steel 316L

This is the industry standard for watches, striking a great balance between durability and cost. It's therefore an excellent overall choice.

Composition: Iron (60 - 70%), Chromium (16 - 18%), Nickel (10 - 14%), Molybdenum (2 - 3%), Carbon (≤ 0.03% “L” = Low)

Hardness: 150 - 220 HV

Weight density: 8.0 g/cm³

Advantages:

✅ Relatively inexpensive (relatively easy to machine)

✅ Good durability

✅ Excellent corrosion resistance

✅ Very good saltwater resistance

✅ Easy to polish and refinish

✅ Good value retention for pre-owned watches

✅ Hypoallergenic for most people

Disadvantages:

❌ Over decades: not entirely resistant to saltwater and chlorine

❌ Scratches relatively easily compared with hardened steels

Stainless Steel 904L & similar marine-grade steels

Developed originally for marine applications, pharmaceutical and chemical industry, 904L stainless steel mainly offers, at a higher cost, better corrosion resistance to saltwater and chlorine.

Composition: Iron (41 - 51%), Nickel (23 - 28%), Chromium (19 - 23%), Molybdenum (4 - 5%), Copper (1 - 2%), Manganese (≤ 2%), Silicon (≤ 1%), Carbon (≤ 0.02% “L” = Low)

Hardness: 180 - 240 HV (~14% harder than 316L stainless steel)

Weight density: 8.0 g/cm³

Advantages:

✅ Superior corrosion resistance (904L is better than 316L)

✅ Excellent resistance to saltwater (904L is better than 316L)

✅ Better resistance to acids (904L is better than 316L)

✅ Very Good value retention for pre-owned watches

✅ Brighter shine after polishing

✅ Hypoallergenic for most people

Disadvantages:

❌ More expensive (Harder to machine,  Requires more tool wear during manufacturing)

❌ Scratches relatively easily compared with hardened steels, albeit marginally better than 316L steel

Used by: Rolex (called Oystersteel), Omega on some models (called O-Megasteel), Panerai on some models

Stainless Steel 316L with special hardening treatment

* Tegimented (surface hardened 316L stainless steel). Hardness up to 1200 HV. Used by Sinn

* Damasko (ice-hardened 316L stainless steel). Hardness ~710 HV

* Duratect coating on 316L stainless steel -> increased surface hardness & improved scratch resistance. Used by Citizen

Titanium Grade 5

Titanium Grade 5 is the most widely used titanium grade for demanding aerospace, medical and marine applications, offering an exceptional strength-to-weight ratio and excellent corrosion resistance.

Composition: Titanium (88 - 90%), Aluminium (5.5 - 6.8%), Vanadium (3.5 - 4.5%), Iron (≤ 0.4%), Carbon (≤ 0.08%)

Hardness: 330 - 360 HV (86% harder than 316L stainless steel)

Weight density: 4.4 g/cm³ (= nearly twice as light than stainless steel)

Advantages:

✅ Excellent corrosion resistance (better than 904L & 316L stainless steel)

✅ Light weight,

✅ Hypoallergenic

Disadvantages:

❌ More expensive (roughly 10x more expensive per kg than stainless steel)

❌ Scratches easily,

❌ less good value retention for pre-owned watches, relative to stainless steel,

❌ darker tone

Gold 18k (Yellow / Rose / White)

White gold is usually Rhodium-plated. This coating gives it a mirror-like, ultra-bright and cold liquid-silver finish. It is noticeably brighter and more reflective than stainless steel. It is more scratch-resistant than stainless steel and develops tiny, soft micro-scratches.

Rose gold has a modern warm aesthetic and low contrast which softens the look of a watch and complements a wide variety of skin tones. The copper component can react with air, sweat and moisture over time and cause the rose tint to slowly fade back towards standard yellow gold color, unless platinum or ceramic was added to lock the copper in place (e.g. Rolex "Everose gold" includes Platinum. Hublot's "Magic Gold" contains ceramic). It is noticeably softer and therefore more prone to scratches and dings.

Yellow gold has a warm vibrant yellow hue and is chemically highly stable. It does not oxidise or corrode over time and will keep its looks over time. It has a high bling factor which is not to everyone's taste. Because gold is highly malleable its hardness is significantly improved after rolling and stamping (i.e. hardness increases from 120 - 150 to 200 - 240)

Composition:

   yellow gold: Pure Gold (75%), Silver (12.5 - 15%), Copper (10 - 12.5%), Zinc (0 - 1%)

      rose gold: Pure Gold (75%), Copper (20 - 22.25%), Silver (2.75 - 5%)

     white gold: Pure Gold (75%), Palladium (13 - 15%), Silver (5 - 10%), Zinc (1 - 2%)

Hardness:

   yellow gold: 140 - 180 HV (~14% softer than 316L stainless steel)

        rose gold: 130 – 150 HV (~24% softer than 316L stainless steel)

       white gold: 180 – 300 HV (~30% harder than 316L stainless steel)

Weight density:

   yellow gold: 15.5 g/cm³ (nearly twice as heavy as stainless steel)

       rose gold: 15.4 g/cm³ (nearly twice as heavy as stainless steel)

       white gold: 15.5 g/cm³ (nearly twice as heavy as stainless steel)

Advantages:

✅ Prestige

✅ Value retention

✅ Hypoallergenic for most people

Disadvantages:

❌ Expensive

❌ rose and yellow gold noticeably softer than stainless steel

Platinum

Platinum is the ultimate luxury watchmaking metal, prized for its immense weight and a naturally brilliant, bright white luster that never fades. Platinum is hypoallergenic and is incredibly dense on the wrist, sitting far heavier than gold or stainless steel. While it scratches relatively easily, the metal displaces rather than shedding away, developing a highly sought-after satin "patina" over years of wear.

Composition: Platinum (95%), Ruthenium (5%) or Cobalt (5%) or Iridium (5%)

Hardness: 130 - 180 HV (16% softer than 316L stainless steel)

Weight density: 21.4 g/cm³ (about 2.7x heavier than stainless steel)

Advantages:

✅ Extremely dense

✅ Luxurious,

✅ Hypoallergenic

Disadvantages:

❌ Very expensive (also takes 3x longer to machine than 18K gold)

❌ Very heavy,

❌ less good value retention for pre-owned watches, relative to stainless steel,

❌ scratches relatively easily

Silver (925 Sterling)

Composition: Silver (92.5%), Copper (7.5%). Premium watchmakers sometimes replace a portion of the copper with traces of Germanium, Zinc or Silicon to slow down the Silver oxidation process and allow the watch case to retain its brilliant white sheen for much longer without turning black.

Hardness: 75 - 110 HV (~50% softer than 316L stainless steel)

Weight density: 10.4 g/cm³ (= 30% heavier than stainless steel)

Advantages:

✅ Beautiful warm appearance,

Disadvantages:

❌ Very soft, scratches very easily,

❌ less good value retention for pre-owned watches, relative to stainless steel,

❌ Develops a dark patina (tarnish), unless part of the copper is substituted with Germanium, Zinc or Silicon.

Bronze

Bronze has become a highly popular alternative material in modern watchmaking - particularly for dive watches - valued for its distinct marine heritage, mechanical warmth, and deeply personal aging process. Bronze reacts aggressively to oxygen, moisture, humidity and skin acidity.

After a few months, the bright, gold-like surface darkens into a deep, rich brown or green layer of copper carbonate, resulting in a unique pattern. The outer brown or green layer is a protective barrier that seals the underlying metal.

To avoid the bronze oxidation stains your wrist skin, most bronze watches feature a caseback made from an inert material (Stainless steel or Titanium Grade 5) ensuring only the hypoallergenic material touches your skin.

Composition:

   Phosphor bronze (vintage look): Copper (92%), Tin (7.5 - 8.5%), Phosphorus (0.01 - 0.4%)

     Aluminium bronze (slow-aging look): Copper (88 - 92%), Aluminium (6 - 11%), Iron & Nickel (1 - 5%)

Hardness: Phosphor bronze 180 - 210 HV (after spring-tempered or cold-worked hardening process)

                  Aluminium bronze 220 - 260 HV (after heat-treated or alloyed with iron/nickel hardening process)

Weight density: 8.8 g/cm³ (= 10% heavier than stainless steel)

Advantages:

✅ Exceptional high resistance to saltwater corrosion

✅ Highly non-magnetic helping to shield the inside mechanical movement,

✅ The evolving patina helps mask surface blemishes and makes scratches blend seamlessly into the character of the case

Disadvantages:

❌ Bronze oxides against the skin and the copper can leave a temporary, harmless green residue on your wrist

❌ Very heavy,

❌ less good value retention for pre-owned watches, relative to stainless steel,

❌ scratches relatively easily

Ceramic

High-tech ceramic is a premium watchmaking material celebrated for its lightweight feel and extreme surface hardness, making it virtually scratch-proof against daily wear. While it sits much higher on the Vickers scale than stainless steel or gold, its brittle atomic structure means it can shatter if subjected to a severe drop onto a hard surface. Because the color is baked directly into the material at temperatures exceeding 1,400°C, a ceramic watch case will never fade, tarnish, or show signs of aging.

Composition: Zirconium + Hafnium Dioxides (94 - 95%), Yttrium Oxide (4.5 - 5.5%), Aluminium Oxide (≤ 0.5%), Color pigments (0 - 5%).

Hardness: 1200 - 2000 HV

Weight density: 5.8 - 6.1g/cm³ (= 25% lighter than stainless steel)

Advantages:

✅ Extremely scratch resistant,

✅ Excellent resistance to corrosion, saltwater, chlorine, sweat, UV

Disadvantages:

❌ brittle (can chip, crack or shatter under severe impact),

❌ less good value retention for pre-owned watches, relative to stainless steel

Carbon (forged)

Forged carbon is an ultra-lightweight, high-performance material made by compressing shredded carbon fiber threads with a resin under immense heat and pressure. It features a distinctive, marbled aesthetic unique to every individual watch case. While it possesses exceptional tensile strength and superior scratch resistance compared to traditional metals, its incredibly low density gives it a stealthy, featherlight feel on the wrist.

Composition: Carbon fibre tows (60 - 70%), Polymer matrix resin (30 - 40%)

Hardness: 30 - 110 HV. On the Vickers scale, forged carbon rates quite low because the tester's diamond pyramid presses into the soft polymer resin matrix rather than the incredibly hard carbon fibers themselves. Despite the low structural hardness score, it resists visible scratches exceptionally well because the dark, marbled pattern masks surface wear, and the carbon filaments deflect everyday abrasions

Weight density: 1.4 - 1.8 g/cm³ (= 5 times lighter than stainless steel)

Advantages:

✅ Excellent resistance to corrosion, saltwater, sweat, UV,

✅ Incredibly tough and resistant to shattering from impacts

✅ Ultra light,

Disadvantages:

❌ Non-repairable: If the case receives a deep gouge or chip, it cannot be repaired, but will need to be replaced

❌ Lack of traditional Luxury Feel,

❌ less good value retention for pre-owned watches, relative to stainless steel,

❌ Micro-Pore Vulnerability: Lower-tier manufacturing can trap tiny air bubbles (micro-voids) during pressing, which can slowly trap dirt, oils, or moisture over years of daily wear.

Sapphire

This is the premium standard for luxury and mid-tier watches thanks to its unmatched scratch resistance. Sapphire isn't glass, but a synthetic transparent crystalline structure made by fusing pure aluminum oxide powder at extremely high temperatures.

Mohs hardness score: 9 (just below diamond)

Advantages:

✅ Exceptional scratch resistance: it can't be scratched by everyday materials like steel, concrete walls, pavement, sand, coins,

✅ Excellent resistance to UV: it will not turn yellow or discolour or haze.

Disadvantages:

❌ Expensive (costly to synthetically grow, slice with diamond saws and polish),

❌ Brittle: a violent drop can cause the entire crystal to chip or shatter, because the structure is not flexible,

❌ To remove a scratch on a sapphire crystal, the entire sapphire crystal needs to be replaced,

❌ Highly reflective thus requiring Anti-Reflective coating to reduce reflection and improve legibility

Hardened Mineral Crystals

These are specialized, chemically or thermally altered glasses engineered by specific watch houses to bridge the gap between costly sapphire and soft ordinary glass. Examples: Seiko's Hardlex

Mohs hardness score: 6 - 6.5

Advantages:

✅ Superb shock impact absorption capacity as the crystal flexes. Great choice for rugged tool, field and dive watches,

✅ Moderate scratch resistance: it can't be scratched by objects made of mild steel (5.5 Mohs) e.g. car keys, copper coins (3 Mohs)

✅ Excellent value /cost ratio,

Disadvantages:

❌ Prone to visible scratches: it can be scratched by concrete walls, hardened steel, sand which often contains particles of quartz (7 Mohs)

❌ Not possible to polish out any scratches

Standard Mineral Glass

This is basic silica glass that has been lightly tempered. It is the default crystal found on the vast majority of entry-level and fashion watches.

Mohs hardness score: 5 

Advantages:

✅ Cheap to produce and shape,

✅ Decent impact resistance with a clean glassy look

Disadvantages:

❌ Low scratch resistance: it can get scratched by mild steel (5.5 Mohs), metal doors / desks etc

Acrylic - Hesalite - Plexiglass

Acrylic / Hesalite / Plexiglass is a transparent plastic polymer. While it is the cheapest to manufacture, it is still highly respected by collectors because it is used intentionally on high-end vintage reissues (like the Omega Speedmaster) for historical accuracy.

Mohs hardness score: 3

Advantages:

✅ Excellent resistance to corrosion, saltwater, sweat, UV,

✅ Incredibly tough and resistant to shattering from impacts

✅ Easy to polish out scratches using an abrasive paste

✅ Ultra light,

Disadvantages:

❌ Very low scratch resistance: it easily scratches from minor daily brushes against clothing zippers, desk edges, or rough paper

❌ Lower quality variants can slowly become yellow or cloudy after years of UV exposure,

‍AR (Anti-Reflective) Coating

AR coatings help reduce the mirror reflection effect of (sapphire) crystals and are applied via Physical Vapor Deposition (PVD) using microscopic layers of transparent metal oxides. Applying multiple alternating layers of high and low refractive index materials make the crystal look virtually invisible.

Standard AR coatings have a 5 - 6 Mohs hardness score

Premium AR coatings have a 7 - 7.5 Mohs hardness core.

Because of the coating's scratch vulnerability, watch brands use strategic placement options based on the watch's intended environment:

• Inside Only (Best Longevity): The industry preferred standard for tool and everyday sports watches: as the AR-coating is sealed inside the case, it can never be scratched by external elements, keeping the crystal looking flawless forever
• Outside Only: Extremely rare and generally avoided, as it reflects light from the internal sapphire interface while remaining fully exposed to external scratches
• Both Sides (Maximum Clarity): i it eliminates up to 99% of visible light reflections, making the crystal look entirely invisible. The trade-off is that the external layer will eventually develop hairline scratches