Amethyst is the only stone in the anniversary Royal Oak gem set drawn from a common mineral. Quartz is the most abundant gem-forming species on earth, and amethyst is quartz coloured violet by iron and natural irradiation. That was not always its position. Until Brazilian deposits opened in the early nineteenth century amethyst was traded alongside emerald and ruby and reserved for ecclesiastical and royal use, and the discovery of large supply collapsed a value that had held for centuries. Choosing it for a set otherwise built from corundums, beryls, garnets and chrysoberyl is therefore a deliberate departure, and one that reads differently depending on whether a collector knows the history. Purple is also the only appearance of the colour anywhere in the ten. The set includes no second violet stone to compare it against, and the closest relation is not another anniversary reference at all but the smoky quartz in one of the multi-stone versions of the same case, which is the same mineral in a different colour.
The case is 41 mm across and 11.6 mm thick in white gold, with the octagonal bezel gem-set in baguette-cut amethysts. The height exceeds the 10.5 mm the selfwinding Royal Oak runs to at the same diameter, and the difference comes from 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 continuous run of rectangular stones breaks and resumes at each. The dial is white gold set with baguette-cut amethysts across its whole surface and carries no applied hour-markers. The stones are the dial, and the white gold Royal Oak hands are the only element above them. The bracelet continues the setting to the clasp, tapering from the case, closing on an AP folding clasp. Amethyst is the softest of the ten alongside tanzanite, and its colour is heat-sensitive in a way the other stones are not, since sustained heat drives violet quartz toward yellow. Practically that means the watch should be kept away from anything that would warm the stones significantly, which is a constraint that applies to this reference and to no other in the set.
The function set is hours, minutes and centre seconds. There is no date, and the omission follows from the dial rather than from the movement: an aperture would break a continuous stone surface at the point where the run most needs to remain unbroken. Centre seconds keeps all three hands on one axis and avoids the second circular break a small seconds subdial would impose. The time is read from hand position against the case, because the dial gives no reference points. Amethyst sits at a middle depth of tone, darker than the pink and yellow stones and lighter than emerald or ruby, and the white gold hands hold against it reliably. Quartz is also less refractive than the corundums and garnets in the set, so the dial returns light more evenly and with less flash, which makes the hands easier to follow than they are on the brighter stones.
The Royal Oak is the collection Audemars Piguet is built on, and the anniversary gem set is the most concentrated piece of gem-setting the collection has carried. Ten stones were used: amethyst, ruby, blue sapphire, emerald, tsavorite, tanzanite, blue topaz, pink tourmaline, yellow chrysoberyl and orange spessartite. Each was issued at 41 mm at this reference and again at 37 mm at 15554, giving twenty references built on one construction across two sizes. Two further 41 mm references stand outside the anniversary designation and use graded combinations rather than a single stone, one pairing black sapphires with tsavorites and smoky quartz, the other graded blue sapphires with Swiss blue topaz. The 15512 approaches the same anniversary brief differently again, using brilliant-cut graded blue sapphires with a diamond-set bezel and retaining the date.
This reference suits a collector who is buying the colour rather than the material. Amethyst does not carry the scarcity argument that tsavorite or tanzanite carry, and it does not carry the hardness argument that ruby and sapphire carry, so the reason to choose it is that violet is the colour wanted and there is no other stone in the set that provides it. That is a clearer motivation than it sounds, and it removes a layer of justification that the rarer stones invite. The history is available to anyone who wants it, since amethyst spent most of recorded time as a stone of the first rank and lost that position to supply rather than to fashion. It appeals to someone who wants a gem-set Royal Oak in a colour the collection otherwise never uses. 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.
