The reference 26585CB is the watch in which two of Audemars Piguet's most demanding production achievements converge in a single configuration of thirty examples: the white ceramic case and integrated bracelet — whose finishing alone requires 30 hours, which is five times longer than for the steel version, and whose ceramic bracelet was only made possible after 600 hours of R&D — and the openworked Royal Oak Perpetual Calendar movement, the Calibre 5135, whose skeletonized architecture removes material from the 5134 base movement while maintaining the full perpetual calendar display through a see-through sapphire dial. The black ceramic openworked perpetual calendar (the 26585CE) established both achievements simultaneously in 2021; the 26585CB extends the same combination to white ceramic in a thirty-piece edition whose specific collector significance is the compound rarity of white ceramic case construction at the highest technical level of the Royal Oak Perpetual Calendar's current production. The first full white ceramic Royal Oak Perpetual Calendar, the 26579CB, was introduced in 2019 and described as a non-limited boutique exclusive. The 26585CB adds the openworked dial and movement to the white ceramic attire, concentrating the ceramic development's full ambition into the configuration whose thirty examples make it the most restricted white ceramic Royal Oak Perpetual Calendar production Audemars Piguet has undertaken.
Delivering the same level of details on a ceramic case and bracelet as found on a steel Royal Oak is nothing short of an achievement. This statement, made in Monochrome's authoritative review of the first white ceramic Royal Oak Perpetual Calendar, applies with compounded force to the 26585CB: the white ceramic's hand-finishing program must reproduce the Royal Oak's full alternating polished and brushed finishing vocabulary — polished bevels along the edges, satin-brushed mid-case, and vertically brushed surfaces on the bezel — in a material whose hardness and abrasion resistance require machining approaches specific to ceramic at every stage of the finishing sequence. The polished bevels on white ceramic are machined against a material substantially harder than the steel or gold whose bevel edges the same tooling produces in standard production; the visual result when correctly executed is a case whose surface quality is indistinguishable from the steel version in the finished state while representing a fundamentally different — and more demanding — manufacturing pathway to that result. The integrated bracelet's assembly demands 30 hours, in white ceramic as in black, the same ceramic bracelet challenge applying regardless of the specific ceramic colorant, with the white ceramic's specific oxide composition producing the cool, light, slightly luminous surface whose character is different from the black ceramic's deep absorption and from the blue ceramic's chromatic saturation.
The openworked Calibre 5135 is the movement derived from the Calibre 5134 of the standard Royal Oak Perpetual Calendar through the openworking process: the removal of material from the bridges, plates, and other structural elements at positions whose structural integrity is maintained while the movement's internal architecture is exposed to view through the sapphire dial from the front and through the sapphire caseback from the rear. The Cal. 5135 has undergone extensive open-working, boasting an intricate assembly of 374 components and a 40-hour power reserve. Against the white ceramic case's specific cool, slightly luminous surface, the rose gold applied hour markers and Royal Oak hands with luminescent coating provide the warm precious metal accents that the white ceramic and the openworked movement's own cool architecture frame from the case's exterior and the movement's interior simultaneously: warm rose gold against white ceramic, the warmth of the markers and hands amplified by the surrounding cool material in the warm-on-cool relationship that white ceramic and rose gold produce across the Royal Oak's dial surface.
The perpetual calendar's full display program is present in the 26585CB as in the 26579CB and 26585CE: hours and minutes on the central axis, date at 3 o'clock, weekday at 9 o'clock, month and leap year at 12 o'clock, moon phase at 6 o'clock, and week number on the periphery of the movement at the inner bezel. The moon phase indicator in aventurine — the glass material whose suspended metallic particles produce the natural star-field glitter effect that the moon phase's night sky requires — is the dial's most materially specific element within the perpetual calendar's display architecture, the aventurine's specific optical character providing the astronomical reference without the enamel work that other moon phase implementations use. The perpetual calendar mechanism's program wheel automatically advances all indications correctly through every month through 2100 without any manual correction required.
The white ceramic case measures 41mm in diameter and 9.5mm in height, consistent with the non-openworked white ceramic Royal Oak Perpetual Calendar, with the openworked version at 9.9mm in height, the additional 0.4mm a consequence of the openworked movement's specific architecture and the sapphire dial's own dimensionality within the case. Water resistance is 20 meters through the screw-locked crown and sealed case construction. The white ceramic integrated bracelet with AP folding clasp completes the watch in the all-ceramic construction whose total wrist weight — ceramic's specific density is lower than steel's and substantially lower than gold's — produces the specific lightness that both the white and black ceramic Royal Oak Perpetual Calendars are consistently cited for in hands-on reviews.
The 26585CB's thirty-piece production concentrates the white ceramic Royal Oak Perpetual Calendar's material ambition into the configuration most demanding to produce, in a quantity whose scarcity is more absolute than the non-limited boutique-exclusive production of the 26579CB. For the collector who approaches the Royal Oak Perpetual Calendar through the ceramic chapter of its production history — the sequence that began with the 2017 black ceramic 26579CE and advanced to the 2019 white ceramic 26579CB and the 2021 openworked black ceramic 26585CE — the 26585CB is the configuration that completes this chapter in the white ceramic material at the openworked technical level, in the production number that acknowledges the achievement's specific difficulty.
