ROLEX PERPETUAL BULGING BACK 18k Rose Gold 1950s

Patent No. 144350.
Filed in 1929 by Rolex, this marked the company’s first application for a self-winding mechanism—
a development that would fundamentally reshape the watch industry.

This evolution led to the perpetual system that would later define the brand.
The first patent concerning the automatic rotor—Patent No. 160492—
is widely attributed to Emil Borer of Aegler.

Further advancement came with Patent No. 170803, filed in 1933, which established the foundation of the rotor system later associated with the “Bubbleback.”

This mechanism enabled bidirectional winding through two reversing wheels, each fitted to prevent counter-rotation, ensuring efficient transmission of energy regardless of direction.

Power from the rotor was transferred to the mainspring via ratchet-equipped gears, minimizing backlash, while additional components—
including a three-armed, curved disc—
allowed the automatic module to be mounted above the movement’s primary gear train.

This vertical layering required additional height, making it necessary to expand the caseback.
This structural necessity is the origin of the Bubbleback form.

The first Bubbleback models appeared in 1933.

Early examples featured engraved instructions inside the caseback, guiding watchmakers during disassembly from the rotor side—
a practical solution for what was, at the time, an unfamiliar construction.

These markings disappeared in the second generation,
and by the third, the movement had evolved into Caliber 620, introducing the NA size for the first time.

As other manufacturers began downsizing their calibers
to enable broader model variations, Rolex followed with similar developments.

In 1936, the reduced-size AR movement—Caliber 520—was introduced.
That same year also saw the debut of the 530AR, a center-seconds movement for ladies’ models.

The present model emerges from this lineage.

Ref. 4643
Produced for only six years, from 1946 to 1952, it stands as a rare example of a rectangular Rolex.

Crafted in solid 18k rose gold, its case exhibits a rich, deep-toned luster with strong visual presence.

Despite its 28mm dimensions, its proportions give the impression of a 34mm round watch.

While it features a perpetual mechanism, it does not conform to the Bubbleback structure.

Instead, it employs a square case with a subtle curvature—
often mistaken for a Bubbleback, but fundamentally different.

The essence of the Bubbleback lies in three defining elements: a domed caseback, water resistance, and a perpetual (self-winding) system.
These characteristics were clearly communicated by Rolex in period advertising.

This reference, therefore, must be understood on its own terms.

At its core lies the significance of Caliber 520AR.

From its early years, Rolex implemented a system
in which discrepancies between movement production and case availability were managed by fitting older movements into newer cases.

This was not incidental, but a deliberate and efficient operational strategy.

In this piece, a movement produced in 1936 was installed into a watch assembled in 1946.

This detail reflects more than specification—
it reveals the essence of Rolex as a company: a family-run enterprise built on precision, discipline, and a long-term vision for sustainable success.

- wrist size in our picture is 17cm circumference -