The bezel on this watch is the same on every example and the dial is not. Reference 278343RBR is the 31mm Datejust in a combination of stainless steel and yellow gold with a domed bezel set with diamonds, and this configuration carries a black mother-of-pearl dial with diamond markers in gold settings and no numerals, on the Oyster bracelet. The stones around the crystal are cut and set to a fixed pattern that Rolex can repeat indefinitely. The surface underneath them came out of a shell and cannot be repeated at all. Two examples of this exact specification, assembled in the same week, will not have the same dial. That is the most unusual thing about the reference in this form, and it is easy to miss because the bezel is what the eye reaches first.
Nacre is selected rather than produced, and that is the whole reason for the variation. It is the inner lining of a shell, laid down in fine plates that break light apart as it passes through them rather than bouncing it off a surface, so what the dial shows is interference rather than reflection. Black nacre works differently from white. Where a pale dial shimmers more or less continuously across its whole face, a dark one holds close to black through most angles and then releases sudden flashes of green, blue and violet when the wrist reaches the right position. The result is a dial that is quiet most of the time and briefly not. Rolex cuts these blanks thin and backs them so the tone stays even, and it sets the diamond markers into solid gold surrounds seated low against the surface, since a tall setting on a 31mm dial begins to crowd the hands before it begins to look generous. Those gold surrounds also tie the dial back to the case, which is steel with gold at the bezel, the crown, the bracelet center rows, the marker settings and the hands, all of it solid rather than plated. The Oyster bracelet is three broad flat links, brushed across the top with polished flanks, closing on a concealed clasp folded inside the links. The date sits at three beneath the Cyclops on a disc matched to the dial.
With no numerals printed anywhere, the date window is the only fixed character on the dial, and Rolex treats it accordingly. The disc behind it is matched to the black ground rather than left pale, so the aperture does not cut a bright rectangle into a dark surface, and the frame around it is drawn for this diameter instead of scaled down from a wider one. The date advances in an instant at midnight rather than drifting through the hours on either side, which is the function the model introduced in 1945 and the one it takes its name from. Above the window the Cyclops lens, fitted since 1953, enlarges the numeral roughly two and a half times, and that magnification does more work on a dial like this one than on a pale dial, because a dark surface gives the eye less to read the numeral against. Setting the date runs through the winding crown at its own position, leaving the hands where they are. The movement is self-winding with a power reserve of approximately 55 hours, built for a case this width rather than inherited from a larger one, since a narrower barrel stores less energy and a lighter rotor takes in less of it from the same arm. The crown screws down against the case.
The Datejust has run continuously since 1945, when it became the first self-winding wristwatch to show the date through a window on the dial. The 31mm case sits between the 28mm Lady-Datejust and the 36mm original, and the 278000 generation replaced the 178000 series in 2018 with a revised case and bracelet. Rolex registered the name for its steel and gold construction in 1933, on the reasoning that steel supplies the structure and gold supplies everything the eye takes in. Mother-of-pearl entered the range as a dial material decades ago and has never been a volume option, in large part because the yield is poor. A shell gives up only a limited area of usable material, and dark nacre of an even tone is scarcer than pale. That has kept these dials in the catalogue continuously without ever making them common. Within the generation, 278343RBR is the steel and yellow gold reference wearing the diamond-set domed bezel, and the black nacre ground is offered on it only with set markers, never with a Roman sequence. Gem-set bezels and gem-set dials are also handled differently in service, since a bezel can be reworked without opening the case while a nacre dial cannot be replaced with an identical one at all.
The buyer for this is choosing a watch that will not look the same twice, and accepting that the choice cannot really be made from a photograph. Nacre has to be seen moving, and two examples on the same shelf can differ from each other more than two different dial colors would. That puts the emphasis on handling the specific watch rather than the specification. Beyond that the appeal is direct. A black ground gives the marker stones and the bezel stones the deepest field the reference offers, so the diamonds separate completely and never compete with the surface they sit on. The Oyster keeps the wrist plain underneath and leaves the head as the only place anything is happening, which suits a dial that already carries an unpredictable element. Buyers who looked at the dark grey version and wanted the same depth with something moving inside it arrive here. Those who wanted a dial that behaves identically every day generally go back.
