Scratch-proof watch. You were sold this with ultra-stylish names like DiaSHIELD, Tegiment, or Duratect. You were promised that your watch would emerge immaculate after dragging it through gravel. The reality is more nuanced, and brands deliberately maintain confusion between two properties of materials that are often opposed: hardness and toughness. We're going to break it all down with Vickers scale data to understand what really lies behind these marketing names.
Hardness and toughness: the confusion maintained by marketing
In the customer's mind, "solid" means it doesn't scratch. But in metallurgy, things are much more complex. Hardness is the ability of a material to resist the penetration of a sharp object. It is measured on the Vickers scale, in HV units. The higher the number, the more resistant the surface is to scratches.
Toughness is the ability to absorb energy before fracturing, its elasticity, its ductility. 316L stainless steel is excellent in this regard: if you violently hit your watch against a table corner, the steel absorbs the energy by deforming slightly. There will be a mark, but the case won't crack. The watch remains waterproof. The movement is protected.
The fundamental problem: the harder a material is made, the more brittle it becomes. Ceramic is 1200 to 1400 HV, which is six to seven times harder than steel, but if you drop it, it breaks clean because it cannot deform to absorb the shock. This is the constant compromise between hardness and toughness.
For reference, here are the basic values. Standard 316L stainless steel is approximately 190 HV. Grade 2 titanium is 160 HV, therefore softer than steel. Grade 5 titanium goes up to 400 HV. Sapphire crystal is approximately 2200 HV. Diamond is 10,000 HV. The goal of all the treatments we will review is to take a base metal under 200 HV and boost its surface to reach 1000, 1200 or even 2000 HV, almost to the level of sapphire.
The eggshell effect: the problem nobody explains
Before going into the details of each treatment, it is important to understand a key concept. Imagine painting a sponge with a layer of hard varnish. If you brush the varnish lightly, it resists. But if you press hard with your finger on the sponge, the sponge underneath compresses and the rigid varnish cannot follow the deformation. It cracks and flakes like an eggshell.
This is often what happens with the simplest surface treatments. At the first real impact, a table corner for example, the soft metal underneath slightly dents and the coating breaks. And it's irreparable: if you polish it, you create a difference in shade between the treated and polished areas. The result is even more visible than a simple scratch.
The real technical question to ask when evaluating a treatment is not what the surface hardness is, but how this hardening is supported by the material underneath. Have we just placed a hard shell on something soft, or have we really hardened the material in depth? This is where the diverging philosophies between Japanese and German brands lie.
DiaSHIELD (Seiko): effective on micro-scratches, limited on the rest
On Seiko's Prospex and Presage lines, you will often see the mention DiaSHIELD. Concretely, the metal is bombarded with ions in a vacuum chamber to deposit a thin, transparent film based on carbon and titanium. This achieves a surface finish of 500 to 600 HV, which is 300 to 400 HV more than raw steel.
This is effective for everyday micro-scratches, such as rubbing your shirt on a desk or cleaning the watch with a slightly dusty cloth. The watch retains its shiny appearance longer. But 500 to 600 HV is not enough to resist an abrasive stone or sand. And above all, it's a thin coating on a soft metal: the eggshell effect is at its maximum.
If you bump a DiaSHIELD watch against a hard corner, you will inevitably have an impact and the treatment will create a kind of crack, sometimes microscopic, or a strange reflection around the impact. And as mentioned above, if you polish it to erase it, you create a lighter spot than the rest of the case. This is why, personally, raw steel without treatment is preferable to a watch with DiaSHIELD, because a scratch on raw steel can be repaired, whereas a scratch on DiaSHIELD creates a permanent and irreparable problem.
Duratect MRK (Citizen): when metal is truly modified
Citizen goes a lot more technical in depth. Be careful though: the term Super Titanium is a generic marketing term that covers several Duratect treatments, not all of which are equal.
Basic Duratect is a titanium carbide coating that can reach 1000 HV. It's better than DiaSHIELD, but the principle is the same: a layer deposited on a soft metal. The same flaws apply.
Duratect MRK, that's another category. Here, we don't deposit a layer; we perform gas diffusion. The finished titanium case is placed in a high-pressure furnace into which a mixture of nitrogen and oxygen is injected. These atoms penetrate the metal's crystalline structure, creating enormous internal stresses that block the movement of dislocations—those microscopic defects that allow metal to deform.
The result is a hardened layer 20 to 30 microns deep, reaching 1500 HV. But more importantly, there's no abrupt junction between a hard layer and a soft core. The atoms penetrate gradually, creating a hardness gradient. The eggshell effect is drastically reduced. This is technically superior to DiaSHIELD in every way.
On high-end watches like the ProMaster Marine 1000M, Citizen even combines MRK with a DLC layer on top, reaching 2000 HV on the surface with MRK as a foundation to prevent the DLC from cracking under pressure. If you're looking for the best scratch resistance on titanium that will withstand shocks, you absolutely must look for the MRK mention from Citizen. It's one of the best technical value propositions on the market.
Double Hardening Casio MRG: the metallurgical masterpiece
Casio G-Shock MRG watches cost between 3000 and 8000 euros. This is a significant budget, but from a purely metallurgical point of view, it is a masterpiece. Casio uses a two-step strategy they call Double Hardening.
The first step is very similar to Citizen's Duratect MRK but adapted to their specific titanium alloy. The titanium is bombarded with nitrogen and oxygen at high temperatures, creating a diffusion layer rich in titanium nitride. The base titanium goes from 160 to about 800 to 1000 HV on the superficial layer. This foundation is crucial because it prevents indentation during a violent impact. Without it, anything placed on top of a soft metal would break.
Once the case is hardened in depth, Casio applies the finishing layer. On black models, it's DLC, amorphous carbon, with a surface hardness of over 2000 HV, almost as hard as sapphire. On other models, they use their patented Arc Ion Plating technology, which uses a high-intensity electric arc to create an ultra-dense plasma. The adhesion is much superior to standard PVD or DLC, which explains the unique colors Casio can offer on its MRG watches.
Tegiment (Sinn): German-style hardened steel
We leave Japan for Germany, and the philosophy changes radically. Sinn uses Tegiment, an industrial process known as Cold Rising developed by the company Bodycote. Unlike DiaSHIELD or DLC, Tegiment is not a coating. No layer is added to the metal. It is the metal itself that is transformed.
To understand Tegiment, one must first understand a chemical problem. Normally, a carbon injector in stainless steel at high temperatures creates chromium carbides. Chromium, trapped in these carbides, can no longer protect the steel against corrosion. The watch rusts like any ordinary steel.
The genius of Tegiment is to work at a very low temperature for metallurgy, between 400 and 500 degrees Celsius. At this temperature, carbon can enter the steel but does not have enough energy to fuse with chromium. It forces its way between the steel atoms, creating an ultra-compressed structure called the S-phase. Imagine a crowded subway car where 50 more people are forced to enter. No one can move, everyone is under pressure. It is this internal tension that makes the surface extremely hard.
The result is a hardness of 1200 to 1500 HV on the surface, 20 to 30 microns deep, with the stainlessness perfectly preserved. The drawback: the core of the watch remains soft steel at 200 HV. In a violent impact, the eggshell effect is still possible, even if Tegiment is much more ductile than pure ceramic.
Ice Hardening (Damasko): hardening the entire mass
Damasko was for a time Sinn's supplier of hardened cases. A commercial dispute led the two brands to each develop their own technology, and they are radically different.
Damasko uses a patented nitrogen-enriched steel, derived from Chronidure 30, a steel used by NASA for space shuttle turbopump bearings. To treat it, they perform through-hardening: the case is heated to 1000 degrees Celsius then cooled by sub-zero cryogenic cycles, hence the name Ice Hardening. This process transforms the soft austenitic structure into a much harder martensitic structure, and this throughout the entire mass of the case.
This is the only treatment presented here that changes the hardness of the case throughout its depth, not just on the surface. From the surface to the center of the lugs, the entire watch displays 710 HV. This is not the highest figure in the comparison, far from DLC at 2000 HV, but it is 3.5 times harder than standard 316L steel. And above all, there is no risk of the eggshell effect because the qualities are homogeneous everywhere. Shocks are absorbed much better. And if you deeply scratch the watch, you can have it repolished without creating a difference in shade.
Japanese philosophy versus German philosophy
In summary of the approaches, two philosophies clearly emerge. Japanese brands like Seiko and Citizen focus on maximum surface hardness. The goal is to make the surface as resistant as possible to light scratches and everyday scuffs. The result is immediately noticeable to the owner. But the foundation remains a soft metal, and with a real impact, the limitations are evident.
Germans like Sinn and Damasko aim for overall mechanical coherence. Sinn's Tegiment hardens deeply without adding a layer. Damasko's Ice Hardening hardens the entire mass. Surface figures are sometimes less impressive, but the watch resists shocks better because there's no abrupt junction between hardness and softness.
On paper, the Damasko approach is technically superior. But that doesn't stop one from wanting to buy a Sinn, because Sinn watches have a look that Damasko doesn't, and Tegiment isn't bad either. Technique isn't everything.
What you need to remember before buying
DiaSHIELD and basic Duratect are treatments that are not very optimized. They resist light scratches a little, it's true, but not that much. And once damaged, the appearance is worse than a basic watch without treatment with scratches, because it's irreparable. If you like a watch and it only comes in a DiaSHIELD version, buy it anyway, but be aware of the limitation.
Citizen's Duratect MRK is a truly serious technology. If you're looking for the best scratch resistance on titanium, that's where to look. Casio's Double Hardening on MRG watches is the pinnacle of surface treatment, but the entry price is high. Sinn's Tegiment and Damasko's Ice Hardening are two good technologies for different profiles: Tegiment for scratch resistance, Ice Hardening for shock resistance.
The most important thing in the end: don't let technique alone guide your choice. If a Grade 2 titanium watch makes you dream and you know it will scratch easily, buy it anyway. The main thing is to wear a watch you love, knowing the facts.
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