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A blue glow that owes nothing to chance
Open the sapphire caseback of a well-made watch and you will see this discreet, almost electric sparkle: blued screws, planted like ink punctuations on rhodium-plated bridges. For amateurs, it’s a workshop thrill; for laymen, simple coquetry. The truth? This blue is not makeup, but the tangible trace of an ancestral watchmaking gesture, both technical and poetic. In a watch movement, the blued screws do not only serve to flatter the eye: they tell of a way of doing things, a discipline of fire, a heritage of marine chronometers and master repairers.
The science behind blue
The blue of the screws comes from a heat treatment on the polished steel. Carefully heated to around 290–310°C, the screw heads develop a thin layer of oxide (magnetite) which diffracts light giving this deep blue hue, sometimes tending towards purple depending on the angle. Before that, the craftsman polishes the screw to a mirror: the more perfect the surface, the purer and more homogeneous the blue. Traditionally, it is heated on a brass plate or on a bed of filings, sometimes with a flame, sometimes in the oven. A few degrees too much and the screw turns purple, then gray; a few degrees less and it remains straw. The precision of the gesture gives the nobility of the color.
What are the blued screws actually used for?
- Anti-corrosion protection: the thin oxide layer protects the steel from attacks by humidity and micro-oxidation, essential in a movement where stability is king.
- Mechanical stability: thermal tempering adjusts hardness and limits brittleness. A well-tempered screw is more resistant to repeated tightening and loosening during service.
- Readability for the watchmaker: this blue contrasts with the rhodium-plated bridges and the brass or gold bezels, making it easier to identify the fixing points during assembly.
- Aesthetic signature: it is a code of fine craftsmanship, particularly in Germanic schools (three-quarter platinum, gold screwed chatons and blued screws) and among several traditional Swiss houses.
Real, fake and all shades of blue
Not all blue screws are created equal. To the trained eye, the “living” blue of a fire treatment differs from the “industrial” blue of a modern deposit. Here’s how to get there:
- Traditional heating: slightly changing color depending on the light, possible purplish reflections, natural micro-variations. The heads are often bevelled, the slots chamfered and polished.
- Chemical Blue/PVD: very uniform and cool, perfect to the point of appearing almost flat. It’s clean, stable, less artisanal. We encounter it on more industrial productions.
- Cosmetic tint: on the entry level, some screws can simply be colored. Clues: non-chamfered slot edges, garish color, lack of consistency with the rest of the finishes.
Should we avoid PVD? Not necessarily. As always in watchmaking, the important thing is the honesty of the statement: a watch with an assumed industrial positioning can adopt a deposit blue. But if we talk to you about the art of fire and “master’s blue”, we expect real thermal bluing.
A heritage of the navy and Breguet
In the 18th and 19th centuries, the fight against corrosion on board ships forged the standard for marine chronometers: blued steel was common, both for durability and readability. Abraham-Louis Breguet also popularized the use of blued elements – we think of the famous “blue hairspring”, the balance spring thermally blued to improve its stability and protect it from rust. In the Glashütte valley, the German school perpetuates this language: three-quarter platinum, screwed gold bezels, blued screws. A. Lange & Söhne, Glashütte Original, NOMOS and others have made it a cultural marker. On the Swiss side, many classic houses (Breguet, of course, but also independent artisans) still use this blue as a sign of fine work.
Aesthetics: dialogue with finishes
On a rhodium-plated movement with satin-finished Côtes de Genève, the blued screws create a graphic counterpoint. With tight beading, they prick the surface like stars on a winter sky. In the presence of screwed gold bezels, they trace a tri-chromic dialogue: cold gray, warm gold, deep blue. It’s not just pretty — it’s readable, orderly, almost musical. Watch photographers know: a movement without blue loses an octave.
Precision: myth or reality?
Blued screws, by themselves, do not miraculously increase the precision of a watch movement. Their role is indirect: better protection of the steel, stability of the assemblies, perceived quality which, often, goes hand in hand with tighter quality control. Be careful not to confuse it with the timing screws of the old regulating organs: they could be gold, steel or blued, and participated in the inertia of the balance. Today, most modern calibers regulate differently (Microstella masses, serge screws, variable inertia balance wheels).
Recognize beautiful details… and take care of them
- Signs of quality: polished screw heads, softened corners, chamfered slots, homogeneous but lively blue. The alignment of the slots, when present, demonstrates additional perfectionism.
- Maintenance: Never try to “revive” a blue screw yourself. Unfortunate polishing removes the oxide and distorts the color. Leave it to a watchmaker for a full service.
- Daily use: a well-sealed and properly lubricated movement protects its screws. Simply avoid extreme thermal shock and entrust the interventions to certified hands.
Houses and workshops to watch
- A. Lange & Söhne: fire-blued screws, gold screwed chatons, the Glashütte triptych in its most accomplished form.
- Glashütte Original and NOMOS: careful in-house calibers, frequent thermal blue depending on the references.
- Breguet: living heritage of the blue hairspring and thermally blued details in its classic lines.
- Grand Seiko/Seiko (depending on caliber): presence of blued screws on certain references, often in dialogue with a meticulous finish.
- Independents (Kari Voutilainen, Romain Gauthier, among others): traditional bluing and high-quality finishes.
In summary
In a watch movement, the blued screws are witnesses: witnesses of a controlled fire, of a tamed steel, of a culture where technique combines with style. They protect, they structure, they guide the eye and the gesture. They tell of the continuity between marine chronometers, contemporary workshops and the undiminished pleasure of turning your watch over to contemplate its architecture. A little blue on a rhodium-plated bridge, and all watchmaking is reflected there.
