55 Years of Citizen Watch Titanium Technology: A Trail of Innovation Paved by Pure Titanium and Duratect

In 1970, Citizen released the X-8 Chronometer, featuring a case made from 99.6% pure titanium. Since then, the company has continued to pursue research and development into pure titanium and its surface treatments, resulting in the development of its proprietary material, Super Titanium™. In 2025, 55 years after the launch of the X-8 Chronometer, Masamasa Hirota, editor-in-chief of Chronos Japan and webChronos and a Citizen titanium watch enthusiast, will explore the history and evolution of the company's titanium technology.

My favorite Citizen watch

　Personally, I'm a big fan of Citizen watches. They're durable, accurate, and, because most of the exterior is made of titanium, they're light and easy to use. I have two Citizen watches hiding on my desk, both of which have titanium exteriors. While this is now commonplace, perhaps it would have been a long time before titanium would have become widespread in the watch industry if Citizen hadn't worked on developing titanium technology. So, I'd like to write a little about Citizen and titanium.

Titanium is an amazing material, but the barriers to practical use are high

　I want to give a bit of a serious review.

　The discovery of titanium dates back to the end of the 18th century. This material is widely distributed throughout the earth's crust, but due to the difficulty of refining it, practical use did not progress for a long time. However, in 1910, American Matthew A. Hunter succeeded in refining titanium for the first time. In the 1930s, the former Soviet Union began using it as part of its plant industry. It was not until the 1940s that large-scale refining became possible. The development of the "Kroll process," which reduces titanium chloride with magnesium, made large-scale titanium refining possible.

　Titanium's light weight, high strength, and corrosion resistance made it ideal for use in aircraft and missile structures. The U.S. Department of Defense recognized the importance of titanium in the early 1950s, and began using it in the construction of the Lockheed U-2 in 1955, the Lockheed SR-71 Blackbird in 1964, and the lunar lander and Saturn V rocket.

Citizen's (reckless) attempt to use titanium in consumer products

　Citizen wondered if titanium could be used in consumer products. Lightweight, strong, and highly corrosion-resistant, titanium was certainly ideal for the exterior of a watch. There had been attempts to use it in dental implants and artificial joints, but Citizen was probably the only manufacturer to consider making it into a purely consumer product.

　The X-8 Chronometer, released in 1970, was the world's first mass-produced titanium watch. The case material chosen was nearly 100% pure titanium. Its electromagnetic balance movement met the standards of the Japan Chronometer Association. However, due to the difficulty of manufacturing, only 2000 units were produced. And, presumably to overcome the issue of fingerprints, silicone oil was applied to the case surface. This was purely an experimental attempt.

　Incidentally, Citizen was also paying attention to materials other than titanium. The Custom V2 Blackie, released in the same year, had a case made of aluminum with a scratch-resistant "hard anodized" surface treatment. It was one-third the weight of stainless steel, and its surface hardness was about twice that of stainless steel. It could be said that the approach of combining lightweight materials with surface treatments, which Citizen is currently good at, dates back to Blackie rather than the X-8.

　Citizen also released the "Adlex" with a natural stone case in 1974. In my opinion, the X-8, Blacky, and Adlex are Citizen's "cult trio," and if you're a Citizen enthusiast, they are models you absolutely must own. Once you have one, you're a Citizen King. However, all of these were overly ambitious attempts, and few remain in decent condition.

Make titanium fashionable with "ATTESA"

　Citizen took on the challenge of using titanium with the X-8, and the 1982 diver's watch "Professional Diver" took full advantage of the material's benefits.

　Despite being water resistant to 1300m and lacking a helium escape valve, the use of titanium made the case lightweight. The surface finish is noteworthy. Perhaps reflecting on the X-8's tendency to attract fingerprints, the entire exterior was heavily blasted. While Citizen subsequently adopted titanium for certain professional use, it wasn't until the 1987 release of the Attesa that the material became a Citizen specialty. This was the driving force behind the widespread adoption of titanium in the watch industry.

　It is speculated that there are two reasons why Citizen became interested in titanium cases. One is the discovery of titanium's high biocompatibility. Not only is it light and rust-resistant, but it is also hypoallergenic, making it the perfect material for watch cases. The other is that in 1982, prior to the Attesa, Japan's Maruman Optical released the world's first eyeglasses with frames made entirely from pure titanium. While it is only speculation, the method of mass-producing titanium frames by forging may have given impetus to Citizen's titanium development. At the very least, Citizen was undergoing a variety of trial and error in processing titanium in the 1980s.

　Unlike previous professional models, the Attesa, released in 1987, was a titanium watch made for the average person. The bracelet and case were integrated, and a new finish gave the surface a soft shine. Citizen had tweaked the rough titanium exterior to make it suitable for the average person. Also, from the 1990s, Citizen began to advertise its watches as "hypoallergenic." However, the graining on the exterior of this model was not as deep as that of later models.

Citizen's titanium is a little different from others.

　Incidentally, since the X-8 in 1970, Citizen has been using more pure titanium (grade 2) than titanium alloy (grade 5). The reason for this is the benefits that pure titanium offers.

-Lightweight: Approximately 40% lighter than stainless steel, making it less tiring to wear for long periods of time.
-Rust resistant: Resistant to sweat and seawater, and rust resistant.
- Hypoallergenic: Hypoallergenic to metals and gentle on the skin.

　However, pure titanium also has its drawbacks.

- Easily scratched: It is softer than stainless steel and is prone to small scratches.
- Difficult to finish: Titanium is difficult to process, difficult to achieve a mirror finish, and the color tends to be dark.

　Since the 1990s, faced with the drawbacks of titanium, Swiss watchmakers have turned to a harder, more easily finished titanium alloy: what the watch industry calls Grade 5 titanium, also known as Titanium 64. This material, with added aluminum and vanadium, is easier to work with, at least compared to pure titanium, which means it lends itself well to finishes like graining, essential to luxury watches.

　Citizen, on the other hand, has attempted to address this issue through surface treatment rather than modifying the material itself, and the reason they chose pure titanium, despite the difficulty of doing so, is probably because it is more hypoallergenic.

　After working on surface treatments with the 1970 Custom V2 Blackie, the company began developing ion plating (IP) as a next-generation surface treatment around 1972. In 1977, they released the Mirador, a stainless steel case coated with titanium nitride. Since then, they have continued their research into surface treatments, perfecting Duratect, a surface treatment that dramatically improved wear and scratch resistance. Titanium treated with this new surface treatment was announced in 2000 as what is now known as "Super Titanium™."

　It is about half the weight of stainless steel, but its surface is about five times harder than stainless steel, and it retains the anti-allergenic properties of pure titanium. Furthermore, the new Duratect technology has the advantage of being able to harden the surface without coloring it or roughening the mirror finish. The problem of surface roughness that had always been associated with previous surface treatments was finally solved. In other words, it is now possible to achieve a finish that combines grain and mirror finish, befitting a luxury watch.

　Then, in 2001, they developed Duratect MRK+DLC, a surface treatment that hardens the material itself. By applying this treatment to the entire exterior in 2006, Citizen's pure titanium became as practical as stainless steel without compromising its properties.

What exactly is the unique surface hardening technology "Duratect"?

　Currently, Duratect has three methods, specifically:

- A method of coating the surface to make it less susceptible to scratches.
- A technique that hardens the surface of the material itself, making it less susceptible to scratches.
- A method that combines both.

　Ideally, a combination of both would be the most scratch-resistant. However, Citizen uses different Duratect depending on the purpose. There's no point in making the case of a dress watch harder, and conversely, for an outdoor watch, it would be better to use a harder material. However, no matter what Duratect is used, the surface hardness is an astounding 1000HV. This is about 7 to 8 times harder than pure iron or titanium alloys. It is at least 5 times harder than the stainless steel used in watches.

Duratect coating the surface

　There are nine types of surface coating techniques: Duratect Titanium Carbide, Duratect Platinum, Duratect Gold, Duratect Pink, Duratect Sakura Pink, Duratect Alpha, Duratect DLC, Duratect Amber Yellow and Duratect DLC Blue.

　The first material to be commercialized was titanium carbide, which is highly hypoallergenic. Citizen then developed treatments to complement the dullness of pure titanium, such as platinum and gold, and even added antibacterial properties to Duratect Pink and Duratect Sakura Pink. Incidentally, the most luxurious finish is Duratect Alpha, boasting a hardness of over HV2000. However, this treatment is only available on certain high-end models. Citizen also successfully prototyped a DLC coating, which allows for a uniform black coating, in 1987 (although the prototype material at that time was not titanium). DLC is now the mainstream black coating, but Citizen was ahead of its competitors in this genre as well.

Duratect hardens the surface of the material itself

　Duratect MRK and Duratect MRK Gold are methods for hardening the surface of the material itself.

　Unlike Duratect, which only covers the surface, Duratect MRK hardens the material all the way through. Specifically, gas is sealed in a vacuum device and titanium parts are heat treated to crystallize the surface of the material, forming a hardened layer. The hard surface layer is about 10 times thicker than regular Duratect, making it more resistant to dents than scratches. This method is more suited to outdoor watches than dress watches.

Duratect is a combination of both, so to speak.

　Duratect MRK+DLC is a full version of Duratect.

　By applying Duratect MRK and then coating it with a hard film of Duratect DLC, the watch is extremely resistant to scratches and dents, and is also highly resistant to metal allergies. However, it is more suited to sports watches than dress watches, and is often seen on high-end Promaster watches.

Pure titanium + surface treatment for a unique finish

　Currently, many watch manufacturers are turning to Grade 5 titanium alloys, which are easy to process and have a color similar to stainless steel. However, Citizen has chosen to treat pure titanium. The main reason is that this approach allows them to make the most of titanium's properties. To mitigate this drawback, the company developed the Duratect surface treatment. Initially, it only used scratch-resistant titanium carbide treatments, but later succeeded in adding treatments such as platinum, which creates a brighter shine. However, Citizen does not seem averse to using titanium alloys. The "CITIZEN Brand Watch 100th Anniversary Pocket Watch," released to commemorate the company's 100th anniversary, deliberately forgoes its signature Duratect and instead uses a thoroughly polished titanium alloy.

　Titanium is lightweight, rust-resistant, and extremely hypoallergenic. Citizen has been honing its technology for this material for over 55 years, making it a unique manufacturer worldwide. I would like to share an interesting story that illustrates the uniqueness of this company.

　The lander (lunar lander) used in the world's first private lunar exploration program, HAKUTO-R, uses "Super Titanium™," a material developed exclusively by Citizen. How many watch manufacturers in the world can produce materials used in space?

Geeky Citizen Titanium Model Choices

　For those of you who think Citizen's titanium models are great, Hirota has some recommendations below.

Citizen Attesa "ACT Line Black Titanium™ Series CC4055-65E"

　Citizen Attesa is the global standard for titanium watches, and this model is their flagship. Perhaps with business in mind, the Duratect surface treatment is Duratect DLC, which beautifully preserves the delicate grain. The sapphire crystal bezel and the dial finish, which doesn't hint at the polycarbonate material, give this watch a look that exceeds its price. It's packed with features, including a perpetual calendar, day and date display, 1/20-second chronograph (24-hour), double direct flight (which is actually quite easy to use), world time function (39-hour difference), daylight saving time function, and dual time function.

Citizen Promaster "Mechanical Diver 200m NB6025-59H"

This latest model inherits the design of the legendary Fujitsubo Diver. The exterior is made of pure titanium with Duratect DLC coating. The automatic movement also achieves excellent magnetic resistance of 16,000 A/m by replacing some parts with non-magnetic materials. This watch, including its 12.3mm thickness, is my personal favorite.

The Citizen "AQ4106-00W"

　This model features a Duratect Sakura Pink exterior. It's interesting that this design also has antibacterial properties. The signature washi paper dial has a beautiful texture and vibrant color. It's also lightweight and easy to handle, and boasts exceptional accuracy of ±5 seconds per year.