Method for manufacturing a ceramic-based external horological or jewellery part with patterned decoration

A method for manufacturing a dial of a timepiece, the method consisting of, in order, steps of:

• producing a base plate in a substrate made of a ceramic material, the base plate having a thickness between 0.1 mm and 1.2 mm,
• directly after producing the base plate, mirror polishing the base plate on a display face of the dial to be visible to a user such that the base plate has a shiny appearance,
• directly after the mirror-polishing step, laser machining predefined patterns having a matte appearance on the mirror-polished display face, wherein a surface area of the patterns represents between 40% and 60% of a surface area of the display face and the patterns have a depth between 5 μm and 10 μm,
• directly after the laser-machining step, oxidizing, by heat treatment, the laser-machined, mirror-polished base plate at a temperature between 500 and 1,000 degrees Celsius;
• depositing a transparent or semi-transparent thin layer on the display face, after the oxidizing step;
• and
• depositing a thin layer on a bottom face of the base plate opposite the display face, after the oxidation step, to opacify the substrate,
• wherein, in the machining step, the predefined patterns are obtained by digital image processing, so as to obtain a digital image formed of black pixels and white pixels, said black pixels or white pixels representing the predefined patterns,
• wherein a graphic content of the digital image includes a dendritic shape, such that the patterns machined on the base plate give the base plate a frosted appearance.