Yellow chrysoberyl is the least familiar name in the anniversary Royal Oak gem set and the third hardest material in it, behind only ruby and blue sapphire. Chrysoberyl sits above beryl, garnet, quartz, topaz and tourmaline on the hardness scale, and it is exceeded among natural gem materials only by corundum and diamond. Despite that it is rarely used in commercial jewellery in its plain yellow form, because the species is known almost entirely through its two extraordinary varieties: alexandrite, which changes colour between daylight and incandescent light, and cat's eye chrysoberyl, which shows a single sharp band of reflected light across a domed surface. The ordinary transparent yellow material that this reference uses is the same mineral without either effect, and it is both harder and less recognised than most of what surrounds it in the set. Yellow is the only appearance of the colour among the ten, with no second stone to place it against.
The case is 41 mm across and 11.6 mm thick in white gold, with the octagonal bezel gem-set in baguette-cut yellow chrysoberyls. The height runs above the 10.5 mm the selfwinding Royal Oak reaches at the same diameter, and the additional material is setting rather than movement, since each baguette needs a channel cut into the metal with enough left below it to grip. The eight hexagonal screw positions remain in place and the continuous run of stones breaks and resumes at each. The dial is white gold set with baguette-cut yellow chrysoberyls across its full surface and carries no applied hour-markers. The stones are the dial. Only the white gold Royal Oak hands sit above them. The bracelet carries the same setting along its length, tapering from the case to an AP folding clasp. Yellow against white gold produces a specific effect that none of the other stones reproduce: because the metal is cool and the stone is warm, the dial reads as gold-coloured while the case reads as steel-coloured, and the watch appears to be made of two metals when it is made of one and a mineral. The hardness also shows in the finished surface, since chrysoberyl takes and holds a polish better than the softer stones and the tables stay bright rather than dulling with wear.
The function set is hours, minutes and centre seconds. There is no date, and the absence is a consequence of the dial construction: cutting an aperture through a continuous stone surface would break the setting at the point where the run most needs to remain whole. Centre seconds keeps all three hands on a single axis and avoids a second circular interruption. Time is read from hand position against the case, since the dial offers nothing to read against. Yellow chrysoberyl is one of the paler stones in the set, and white gold hands over a light warm field is a moderate legibility pairing, better than pink tourmaline and worse than emerald or ruby. The hands are found by shape and length as much as by contrast, which is inherent to a dial that has been given over entirely to stone.
The Royal Oak is the collection Audemars Piguet is built on, and the anniversary gem set is the most sustained gem-setting programme the collection has carried. Ten stones were used: yellow chrysoberyl, ruby, blue sapphire, emerald, tsavorite, tanzanite, blue topaz, amethyst, pink tourmaline and orange spessartite. Each was issued at 41 mm at this reference and again at 37 mm at 15554, producing twenty references on the same construction in two case sizes. Yellow and orange sit adjacent in the set and are the only two warm stones that are not red or pink, which makes the chrysoberyl and spessartite references the nearest comparison either has. Two further 41 mm references stand outside the anniversary designation and use graded mixtures instead of a single stone, one of black sapphires with tsavorites and smoky quartz, the other of graded blue sapphires with Swiss blue topaz. The 15512 handles the same brief a third way, with brilliant-cut graded blue sapphires and a diamond-set bezel, and retains the date.
This reference suits a collector who wants the stone to require explanation. Chrysoberyl is not a name that circulates outside gemmology, and a yellow chrysoberyl Royal Oak will be read as a yellow stone by almost everyone who sees it, which is either the appeal or the objection. For a collector who values material properties over recognition it is arguably the best-chosen stone in the set: harder than everything except the two corundums, more durable in daily wear than tanzanite or amethyst, and drawn from a species with genuine standing in gemmology despite its low commercial profile. It appeals to someone who has looked at all ten and chosen on merit rather than on name. 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 rather than to an open catalogue run.
