The dial of this watch is made of ruby, cut down to less than half a millimeter thick. F.P. Journe built twenty of them across 2019 and 2020, in platinum at 40 mm and 9.9 mm deep, and because the material is natural stone every single dial is different from every other. The Coeur de Rubis carries two pieces of ruby, each 0.45 mm thick, laid onto a rhodium-plated brass plate, with guilloche silver under a black gold coating around them. The movement is the calibre 1403 in 18K rose gold: hand wound, a tourbillon with a constant force device and a dead beat seconds, hours and minutes at 3 o'clock, small seconds at 6, power reserve at 12. The reserve runs to forty-two hours from twenty turns of the crown, and the series has not been repeated.
Working stone to 0.45 mm is the whole difficulty and it is worth understanding why. Ruby is corundum, one of the hardest materials that occurs naturally, second only to diamond on the ordinary scale of hardness. That makes it slow to cut and slower to grind, and it does not make it strong. Hardness and toughness are different properties: a hard material resists being scratched, and a tough one resists being broken, and ruby is emphatically the first without being much of the second. Reduce a piece of it to less than half a millimeter thick across the whole area of a watch dial and it becomes something rather closer to a sheet of glass than to a gemstone, capable of cracking under handling pressure that a metal plate would not notice. Every one of the twenty dials had to be cut, thinned, finished and then mounted without that happening even once along the way. The manufacture's own dial house, Les Cadraniers de Geneve, describes it as one of the most difficult dials they have made, and dial houses are not generally given to making that sort of statement about their own work. The rejection rate on a job like this is not published and is unlikely to have been small.
Natural stone creates an unusual situation for a numbered series, and it is worth being precise about what it means. A limited edition normally means twenty identical watches carrying numbers; the whole point of the format is that they match one another. Ruby does not match, and cannot be made to. It is a natural mineral with inclusions, color variation and internal structure that differ from one piece to the next, so twenty dials cut from natural stone produce twenty different faces, and no amount of selection would make them the same. What F.P. Journe has therefore built is a series of twenty watches that are each individually unique, which is a genuinely different proposition from either a limited edition or a one-off, and one the industry has very few examples of. The practical consequence for a buyer is that comparing two examples is not like comparing two of a numbered run: they will differ visibly, one may be preferred to another on its own merits, and the usual assumption that any example of a limited series is interchangeable with any other simply does not apply here at all. Buying one unseen is a different sort of decision from buying an unseen example of anything else in the catalog.
The dates attached to this series are the genuinely interesting part of it, and they are very easy to miss. The Coeur de Rubis was built in 2019 and 2020, on the calibre 1403, which is the tourbillon movement F.P. Journe had been producing since 2003 and which the Souveraine collection lists as running to 2018. In the same period the manufacture launched the vertical tourbillon, an entirely new movement built for the model's twentieth anniversary, with a redesigned carriage and nearly double the reserve. So the Coeur de Rubis is a late run on a movement that had just been superseded, produced alongside its own replacement. That is not an accident of scheduling. The 1403 sits in a 9.9 mm case at 40 mm, where the new calibre needs 13.60 mm at 42, and a dial made of ruby was never going to be built into the larger watch, whose dial is the movement itself. The older movement was the only one that could carry this particular idea, and it appears to have been kept in production long enough to do so. That is a quietly revealing decision about how the manufacture treats a superseded calibre: not as obsolete, but as the right tool for a job the new one cannot take on.
Twenty pieces carrying twenty different dials means the individual example matters a great deal more than usual, so look hard at this one rather than at the model in general. Examine the ruby in daylight from several angles for its color, its inclusions and its evenness, and understand that variation is inherent rather than a fault. Then look for damage, which is the real risk: a chip or a hairline in a 0.45 mm stone dial cannot be repaired and cannot be replaced, and the whole watch is compromised by it. Check the edges carefully where the ruby meets the surrounding coated silver, which is where any handling damage tends to start. Confirm the number within the series and the paperwork that came with it. On the case, examine the platinum at the bezel and along the lug flanks for the rounding that follows repeated polishing. Then wind it fully, twenty turns from empty, and watch the seconds hand step cleanly once a second. Have the carriage inspected by a specialist and establish the service history, since a constant force tourbillon is not work for a general workshop.
