Component record · Plates & finishing

Blued Screws

Verified

Small movement screws heat-treated to a deep blue colour, combining a hardened temper with a decorative, corrosion-resistant surface oxide layer.

What it does

Fasten movement components (bridges, springs, levers) while providing both increased hardness at the tempered stage and a hallmark of fine hand-finishing.

How it works

Polished steel screws are heated to a specific temperature (historically judged by eye from the resulting oxide colour, progressing from straw through purple to blue as temperature rises) which both tempers the steel to a durable hardness and forms a thin, corrosion-resistant blue oxide layer.

Because the colour is a direct visual indicator of temperature reached, consistently blued screws across a movement are taken as a sign of careful, skilled finishing, and remain a mark of quality in high-grade and haute horlogerie movements.

Evolution

A traditional hand-finishing technique from early fine watchmaking, still practised (and sometimes reproduced by chemical or plating means in lower-cost production) in contemporary high-grade watchmaking as a visual quality marker.

Known variations

Traditionally heat-blued (temper-blued) screws
Chemically or electrolytically blued screws (imitative, without the tempering benefit)

Identification for collectors

Genuine heat-blued screws show a deep, slightly uneven blue with a visible temper colour gradient near the screw head; uniform, flat blue across mass-produced screws may indicate chemical bluing rather than heat treatment