Abstract: The present invention relates to a gray gold alloy free of nickel and copper having a hardness that is suitable in particular for watchmakers and jewellers. Said alloy consists of (in wt %): more than 75% of Au; more than 18% to less than 24% of Pd; more than 1% to less than 6% of at least one element selected from among Mn, Hf, Nb, Pt, Ta, V, Zn and Zr; optionally, no more than 0.5% of at least one element selected from among Si, Ga and Ti; and optionally, no more than 0.2% of at least one element selected from among Ru, Ir and Re. The invention also relates to a method for preparing said alloy.

Abstract: The invention relates to a translucent or transparent, colored enamel that contains metal nanoparticles that lost their natural tendency to aggregate with each other, and having a color essentially provided by the reflection of light. The nanoparticles have lost their natural capability to aggregate with each other due to the application of a coating, or because they have been functionalised electrostatically or using highly sterically hindered entities or using hydrophilic entities located at the surface thereof. The nanoparticles may be gold nanoparticles that impart an intense and deep red to said enamel.

Abstract: The present invention relates to a white gold alloy free of nickel and copper having a hardness that is suitable in particular for watchmakers and jewellers. Said alloy consists of (in wt %): more than 75% of Au; more than 18% to less than 24% of Pd; more than 1% to less than 6% of at least one element selected from among Mn, Hf, Nb, Pt, Ta, V, Zn and Zr; optionally, no more than 0.5% of at least one element selected from among Si, Ga and Ti; and optionally, no more than 0.2% of at least one element selected from among Ru, Ir and Re. The invention also relates to a method for preparing said alloy.

Abstract: The invention relates to a translucent or transparent, coloured enamel that contains metal nanoparticles that lost their natural tendency to aggregate with each other, and having a colour essentially provided by the reflection of light. The nanoparticles have lost their natural capability to aggregate with each other due to the application of a coating, or because they have been functionalised electrostatically or using highly sterically hindered entities or using hydrophilic entities located at the surface thereof. The nanoparticles may be gold nanoparticles that impart an intense and deep red to said enamel.