Wer sich wirklich mit der Herstellung der Karamiklünette auseinandersetzen will, der möge sich die Patentschrift US2008/0026207A1 von Rolex zu Gemüte führen. In der Schrift wird der Herstellungsprozeß beschrieben und auch auf die Problematik der roten Keramik (Stichwort blau/rote Lünette) eingegangen, wobei gewisse Kenntnisse in der Werkstoffwissenschaft (die bei mir zugegebenermaßen nur noch rudimentär vorhanden sind) von Vorteil sind.

Hier der sogenannte „Abstract“:
“The invention relates to a piece comprised in part or in full of a pigmented ceramic in which the pigment is comprised of nanoparticles based on a metal from column IB of the periodic table of the elements or of an alkaline metal, or an alloy of both, coated with a layer of silica, the silica being crystalline silica, particularly cristobalite or tridymite. The ceramic is preferably zirconia or alumina. The nanoparticle silica is crystallized, for example, by a thermal treatment in air or under inert gas at temperatures of between 900 DEG C. and 1400 DEG C. The piece is made by sintering a nanoparticle/ceramic mixture in air or under inert gas at temperatures of between 900 DEG C. and 1250 DEG C.”

Und hier der Passus zur Problematik der roten Keramik:
“In particular, it is difficult, if not impossible, to obtain to date certain ranges or varieties of red that are strong, bright and stable through time. Numerous tests have been done in this matter, including using coated nanoparticles, especially silica-coated nanoparticles as pigments, but the final ceramics obtained are still known to have muddy and "dirty" colors, rather similar to an undefined brown. The object of the invention precisely aims to overcome these disadvantages by precisely proposing timepiece components, jewels or jewelry pieces made in ceramic in the entire range of desired colors, particularly in the red range.”

Der von Rolex patentierte Prozeß zur Herstellung roter Keramik ist ausgesprochen kompliziert und sehr aufwendig:
“To manufacture the finished piece, the slip casting method is used by proceeding with filtration under pressure of a stabilized colloidal suspension containing isolated particles of nanostructured yttria zirconia and nanoparticles of pigments at the rate of 2% pigment/zirconia by weight, the proportion by weight of solids in the suspension may be between 10 and 60%.The suspension is then forced by a piston through a ceramic filter covered by a filter under pressure on the order of 10 MPa, which remains constant until all of the suspension is filtered. The piece is dried by dessication until the mass is stabilized, then sintered in air between 1200[deg.] C. and 1300[deg.] C. Thus, a bright red ceramic piece is obtained. Here it is mentioned that the nanoparticles/zirconia weight proportions may vary from 0.5 to 5%, subject to that which is indicated in the following example. The filtration pressure may be spread out from 2 to 20 MPa, and the sintering time varies from 30 minutes to 8 hours, while remaining in the red range.”

Das Problem zur Herstellung der roten Keramik ist wohl gelöst, ob wir aber zukünftig eine blau/rote Lünette bei der GMT-Master II sehen werden ist natürlich auch eine Frage der Wirtschaftlichkeit…..

Gruß
Matthias