Scratch resistance

A scratch is not a defect: it's the trace of a real impact between a surface and something harder. Scratch resistance is measured on the Mohs scale, which ranges from 1 (talc) to 10 (diamond), and on the Vickers scale, used mainly for metals and surface treatments. The two scales are not interchangeable: Mohs is ordinal and qualitative, Vickers is quantitative and linear. Confusing them is a common mistake even in specialized press.

Acrylic crystal stands at around 3-4 Mohs: it scratches with a fingernail, but polishes out with PolyWatch in five minutes. K1 mineral reaches 5, Seiko's Hardlex about 7, synthetic sapphire crystal 9. Harder doesn't necessarily mean better: sapphire is fragile to lateral impacts, acrylic absorbs the blow and yields only at the surface. I've restored dozens of vintage Speedmasters for exactly this reason.

On metals, the matter is different. Untreated 316L steel scratches easily: surface hardness is low. This is why hardening treatments exist. DLC (Diamond-Like Carbon) can multiply hardness up to six times compared to base steel. Sinn's Tegiment, Citizen's Duratect, RZE's UltraHex and the 1,800 Vickers coating of the VPC Type 39VM all work on the same principle: depositing or creating a surface layer harder than the substrate. Duratect TIC, a specific variant for titanium, bears the initials of Titanium Impact Coating and guarantees about five times the resistance of standard stainless steel.

Titanium is a case unto itself. Grade 2 has a natural hardness of about 145 Vickers: it scratches extremely easily. Formex brings it to 900 Vickers with heat treatment. Citizen with Super Titanium and MRK technology works on similar processes, adding resistance to dents as well, not just surface scratches. The result is titanium with behavior close to hardened steel, but at a third the weight.

Technical ceramic already starts at 9 Mohs and doesn't improve with additional treatments: it's the material itself that's hard. Rado, IWC with Ceratanium, Hublot with Magic Gold (gold-ceramic alloy with hardness claimed superior to traditional gold) and Zenith use ceramic precisely to eliminate the problem at its root. The downside is fragility to impacts: ceramic doesn't scratch but chips.

Hairlines—the parallel micro-scratches that appear on brushed finishes—are inevitable. They're not a sign of low material quality: they're proof the watch has been worn. On polished steel they become visible almost immediately; on a shotblasted or satin finish they camouflage themselves and the appearance remains consistent much longer. This is why many modern sports watches favor matte finishes even when the material would be polishable.