Original von Hadoque
... Diese Aussage bestaetigt jedenfalls, dass es ein Problem gibt.

Ob es eine Loesung gibt bleibt spannend.
In der von Chrales. genannten US Patentanmeldung wird ganz speziell auf das Problem mit der roten Färbung bei Keramik eingegangen.

[0003] 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.
[0004] 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.
[0005] 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.
...
[0012] As indicated above, the various attempts made until now utilizing nanoparticles as pigments unfailingly lead to the "dirty" colors mentioned previously, especially in the red range, regardless of the parameters utilized and the care given to developing the ceramic, a phenomenon that is sometimes accompanied by a color shift to blue.
[0013] This may be attributed to, as observed, several factors all intervening during the sintering operation of the ceramic piece: on the one hand, diffusion of metal species across the silica coating when the latter is not crystallized, on the other hand, a phenomenon of coalescence of the nanoparticle cores comprising the pigment when they are polynuclear (see below), and still on the other hand, an agglomeration or agglutination of pigment nanoparticles between them.
[0014] On the contrary, when silica is crystallized, this coating is used as a diffusion barrier for the metal comprising the core when the nanoparticle is subjected to high temperatures. There is no coalescence or agglutination.
[0015] The transformation of amorphous silica into crystallized silica coating the nanoparticles before their utilization as pigments is done by a thermal treatment at a temperature of ...
...
[0017] Surprisingly, there is no migration or coalescence even if the ceramic is developed at a temperature that is markedly greater than that of the melting point of the metal or alloy comprising the nanoparticle core or cores, with a color that remains "clean" and strong.

Und im Patentanspruch Nr. 8 wird auch die mögliche Verwendung für eine Lünette offenbart
8. The piece according to claim 1, wherein the piece consists of a watch container, a dial, a bezel, a bracelet or pins