« What good are blue movement parts in a watch? »
Blue is the color of horology in 2016. That puts the especially high-quality blued steel components back in the spotlight. We explain what makes "blue" so appealing and whether blued watch parts do more than just look good.
The color blue reflects the vastness of the sky and is more precious than gold. For thousands of years, people have been in pursuit of intense shades of blue to color glass, textiles, ceramics and mosaics and to paint expressive pictures. To do so, they used pigments from woad, indigo, azurite and cobalt – all the way to precious lapis lazuli, the blue stone that was ground into ultramarine. Strictly speaking, "ultramarine" means "beyond the sea," describing the long journey the stones had to make before painters could use them to color the Madonna's mantle blue. To this day, genuine ultramarine blue is more expensive than gold. In every era of cultural history, the color of the sky has left its mark, as its rich symbolism and the many expressions built around it show.
The fascination of the blue hour
The blue hour, that fascinating and very brief moment that enchants the world at sunset or sunrise, owes its very special effect to the deep blue color of the sky. For some time now, blue watches have been popular with women and men alike. Sometimes it is just the strap, on other watches the dial, while still others are designed entirely in the colors of the sea. Yet blue plays a completely different role in high-end luxury watches – namely when the hands or screws are not colored, but integrated into the timepiece or chronograph as blued hands and blued screws, as blued steel, as is the case, for example, with the Pesaro II by Bruno Söhnle. Bluing movement parts is a long-standing tradition, so let us take you on a little journey into its history and technique.
Blued steel
When steel parts are heated carefully and slowly to 290° Celsius (a process known as tempering), the previously mouse-gray metal becomes coated with a wafer-thin layer of magnetite. It shimmers cornflower blue and is used in the manufacture of fine watches: blued screws and blued hands are refined in this way – "finished," as specialists call it. When steel is processed and refined, thermal tempering can give it a wide range of temper colors, depending on how long and at what temperature the steel is heated: at 220° Celsius the steel shimmers pale yellow, it 
turns yellowish brown at 245° Celsius. At a temperature of 265° Celsius the color shifts to reddish brown and finally turns blue at 290° Celsius. If the steel is heated further, the temper colors fade and it turns mouse-gray again. The magnetite mentioned above is a stable compound of oxygen and the iron in the steel. Magnetite also occurs as a natural mineral and is resistant to alkalis and acids. A wide variety of blue shades can be produced, depending on how long the steel parts remain in the bluing oven, ranging from very light blue to cornflower blue to the deepest dark blue. Once the desired shade is reached, the parts are quenched in an oil bath, which stops the process.
The properties of magnetite
In the 12th century, Hildegard of Bingen described the properties attributed to magnetite at the time: magnetite was said to activate body and mind and to stimulate the glands as well as the flow of energy. Magnetite supposedly heightened responsiveness, and the stone was also believed to create a relaxing aura. Hildegard of Bingen was convinced that wearing magnetite helped against cramps, tension, heavy sweating and body odor, and against hunger. It was also said to help against inflammation as well as poisoning.
Does bluing protect against rust?
Anyone who thinks blued steel is also more rust-resistant because bluing has already oxidized it is mistaken. So says trained chemist Lucien F. Trueb, who worked for the Neue Zürcher Zeitung for 25 years, tracked down every chemical compound imaginable, and maintains that bluing does not protect the steel parts in a movement from rust. Blued screws, blued hands and springs rust just as much as the untreated material and essentially offer no protection. Since oxygen and water in the form of vapor can penetrate the blue surface layer to reach the iron, rust can form there as well.
Blued steel is a tiny bit softer
Tempering colors not only blued screws and blued hands, but also the steel of sharp knives. Here, tempering serves to take away the steel's glass-hard brittleness and not only blue it, but also make it a little more elastic. The knives then become sharp while remaining spring-hard. Weapons in general were often blued, since it gave them a far more refined appearance. Famous examples include oven-blued Damascus steel, in which the different steels forged together react differently to the heat of the oven and thus shimmer in different shades of blue. Alongside thermal bluing, chemical bluing has also been known since antiquity, in which the metal was blued using alkalis and salts of nitrous acids. Agricola already described the effect of salts as an oxidizing agent in his work "De re metallica," as did Achard in 1788 in "Alliage métallique." These methods, however, play no significant role in the production of watch movement parts.
Beauty is essential – blue is on trend
A perfect watch is not only about a precisely running movement and a flawless case, but also about the aesthetics that go with them: here, the color blue expresses a longing for infinity, even as the hands keep turning relentlessly, proving in their own way that every moment has its very own time. Blued steel is delicate and hard at once, and it captivates with its incomparable sheen. Just how strong the trend is – and not only for tempered metal – is shown by this small selection of fine watches from renowned manufactures. These watches shine not only with blued hands and blued screws, but also with blue dials, complemented by matching straps.
The Breitling Superocean Heritage is just as sporty as the Omega Constellation Globemaster. While Chopard watches previously made do with only a few colors, the blue hands of the Happy Sport practically glow and bring fresh momentum to the line. At Basel 2014, Frédérique Constant also presented the new midnight-blue hands of its classic Manufacture Worldtimer. Through the exhibition caseback of the Maxime Manufacture Slim Line Moonphase, you can see several blued screws of the case.
