After months of trial and error, the end result, achieved by working with the same specialist supplier that creates IWC’s existing ceramic cases, was a ratio that found “the optimal balance between mechanical properties and luminosity”.
However, that was far from the only obstacle that had to be overcome. While standard oxide ceramics are sintered in a normal oxygen-rich atmosphere, it turned out that Super-LumiNova would degrade under those conditions: it needed to be fired in a special mixture of inert gases. “This was really challenging, because that’s not the standard way to sinter zirconium,” says Brunner. “I would say this was the hardest part.”
Having figured out how to make the case and ensure a smooth, uniform shine, the IWC team had to ensure that the end result met the same durability standards expected of a regular ceramic watch, famous for its resistance to corrosion. scratching and the hardness of its surface.
Other watch brands, including Bell & Ross and Zenith, have created fully or partially luminous watch cases by infusing fiberglass, quartz, or carbon polymers with Super-LumiNova. But no one had tried it until now with ceramics. “When you have ceramic, the scratch resistance and durability are on a completely different planet,” says Brunner.
“When we mix zirconium with Super-LumiNova, as materials scientists, we call it (a mixture of) structural ceramics and functional ceramics. Structural ceramics provide the physical stability of the material and functional ceramics provide a specific function, in this case luminosity,” says Brunner. “When you mix two of them, you’re probably going to lose some of the mechanical stability, because when you have 100 percent zirconia, you have full strength.”
“What we discovered is that in terms of hardness, measured with Young’s modulus, we are at the same level. Therefore, the scratch resistance will be exactly the same as that of a standard ceramic. We reduced the fracture toughness a bit; If you drop 100 pieces, the risk of breaking some of them will be greater when you introduce Super-LumiNova. But surprisingly the reduction is not that dramatic. We did all the (normal) testing in-house, with impact tests ranging from 25G to 5000G, and it passed all the tests.”
The longevity of the Ceralume watch’s luminous glow is a direct function of the large amount of Super-LumiNova present; Despite being interspersed with ceramic, it is capable of absorbing a significant amount of energy from sunlight.
Meanwhile, the suitcase is resistant to UV damage. “It depends on the mass,” confirms Brunner. “If you imagine, normally on a standard watch you have hands and maybe some indexes in Super-LumiNova, which is a very low amount: fractions of grams. Here we are talking about a complete case and also on the strap you have more Super-LumiNova.”
The strap, Brunner says, is comparatively simple to design, without the concerns of sintering, shrinkage and color fastness. “Of course, one important thing is that it is completely homogeneous. This is always difficult when you mix, for example, a plastic or a resin with hard particles,” he says.
