Orange spessartite is the brightest stone in the anniversary Royal Oak gem set. Spessartite is a manganese aluminium garnet, and garnets of this species bend light more strongly than beryl, quartz, topaz or tourmaline, which means the same amount of light entering a stone comes back with more intensity. Combined with an orange that is saturated rather than pale, the result is a dial that reads hotter than anything else in the ten. The supply is also recent. Spessartite was a mineralogical curiosity in useful sizes until deposits in Namibia and later Nigeria came on line in the 1990s, and the trade name that followed it into the market dates from that period rather than from any older tradition. Orange is the only appearance of the colour in the set, and there is no second stone anywhere in the ten that approaches it, which makes this the most isolated choice available.
The case is 41 mm across and 11.6 mm thick in white gold, with the octagonal bezel gem-set in baguette-cut orange spessartites. The height sits above the 10.5 mm the selfwinding Royal Oak runs to at the same diameter, and the difference is the setting rather than the movement, since baguettes require channels cut into the metal with material left beneath to hold them. The eight hexagonal screw positions survive, and the run of rectangular stones breaks and resumes at each one. The dial is white gold set with baguette-cut orange spessartites across its whole surface and carries no applied hour-markers. The stones are the dial. The white gold Royal Oak hands are the only element above them. The bracelet continues the same setting to the clasp, tapering from the case and closing on an AP folding clasp. The pairing of a strongly refractive warm stone with a cool white metal is the most emphatic contrast in the set, more so than ruby, because orange sits further from white gold in temperature than red does and returns more light while doing it. Baguette cuts give that light back across broad flat tables rather than scattering it, so the effect is not sparkle but sheets of colour that turn on and off as the wrist moves.
The function set is hours, minutes and centre seconds. There is no date. An aperture cut through a continuous stone surface would break the setting where the run most needs to stay unbroken, so the dial is left whole. Centre seconds keeps all three hands on one axis and avoids the second circular break a small seconds subdial would require. Time is read from hand position against the case, since the dial provides no markers. Orange spessartite is a middle-tone stone and the white gold hands separate from it adequately, but the brightness of the material works against legibility in strong light in a way that the darker stones avoid, because the dial can return enough light to compete with the hands rather than sit behind them. That is the direct cost of the property that makes the reference distinctive.
The Royal Oak is the collection Audemars Piguet is built on, and the anniversary gem set is the most concentrated gem-setting the collection has carried. Ten stones were used: orange spessartite, ruby, blue sapphire, emerald, tsavorite, tanzanite, blue topaz, amethyst, pink tourmaline and yellow chrysoberyl. Each was issued at 41 mm at this reference and again at 37 mm at 15554, giving twenty references on one construction across two sizes. Spessartite and tsavorite are both garnets, which makes them the only two references in the set built on the same mineral group in different colours, and both were commercially unavailable in quantity until the second half of the last century. Two further 41 mm references sit outside the anniversary designation and replace the single stone with graded combinations, one of black sapphires with tsavorites and smoky quartz, the other of graded blue sapphires with Swiss blue topaz. The 15512 takes a different approach again within the same run, using brilliant-cut graded blue sapphires with a diamond-set bezel and keeping the date.
This reference suits a collector who wants the loudest version of the set and knows it. There is no argument for orange spessartite as a restrained choice: it is the brightest stone, the warmest colour, and the only one of its hue, and against white gold it produces a watch that cannot be worn quietly. That is the reason to buy it rather than an objection to it. It appeals to someone who already owns conventional Royal Oaks and wants one that operates at a different register entirely, and to someone interested in a stone whose availability is a matter of recent mining history rather than of long tradition. Anyone comparing it against the tsavorite version is comparing two garnets from the same period of supply, which is a closer relationship than the colours suggest. The 41 mm size is the larger of the two the set offers, with the same stone available at 37 mm. The anniversary designation ties production to the occasion.
