The present invention relates to a method for producing a decorative surface structure, comprising the steps of forming a casting of the surface of a master model in a suitable polymeric material, applying a thin conducting layer to the surface of the casting, and then electroforming the polymeric casting to produce a metallic replica of the desired surface. Such a method is known for example from the CH-A 601 500, wherein items such as a watch face can be produced by an electroforming process whereby a master model of the watch face is made - commonly in metal -, plastic copies of this master are produced by a process such as casting, and subsequent electroformed metal copies are made from the plastic intermediate. This electroforming process allows considerable product enhancement because relief information (for example raised numerals) can be incorporated into the master model, and are thus also copied onto the subsequent elec- troform.

It is also known that decorative effect and surface enhancement can be achieved by means of certain types of hologram and diffractive pattern. The so-called embossed hologram, and a multiplicity of decorative diffraction foils use the presence of a micro-relief structure on a surface to create a surface enhancement which is based on optical diffraction and not on the properties of coloured inks, pigments etc. Such embossed surfaces may be further enhanced by the application of a thin metal layer (for example vacuum coated aluminium). Products such as the embossed hologram and diffraction foil are available in todays marketplace in the form of thin plastic foils which have been embossed using a suitably made embossing master carrying the diffractive information as a surface relief structure, see for example US-A 4 184 700.

From the US-A 4 867 264 is also known an electroforming process for duplicating the surface contour of a master form.

The EP-A 175 460 discloses a method of manufacturing a diffraction grating, utilizing specially adapted steps for it, wherein the master is also a grating.

It is the object of the present invention to improve the quality and the range of the decoration of surfaces, mainly by improving the structure of the master model. This object is attained by the method disclosed in the claims.

The method according to the invention will be described below by way of an example for producing decorated surfaces, in particular of a watch face.

First, a holographic or diffractive relief pattern is formed in a metal surface whereby this step may itself involve producing an electroformed copy of a holographic or diffractive relief pattern recorded using laser technology on a photosensitive surface.

All or parts of this metal relief pattern are then incorporated into a master model of the finally required watch face. In general, this master model will also include non-holographic or non-diffractive areas and elements to provide macroscopic relief effects and surface texturing, and utilitarian features such as apertures for the date wheel and driving axles for the hands. Several different holographic or diffractive elements may be incorporated into different areas of the same watch face.

Castings in a polymer system are produced of the master model surface.

These castings are coated with a suitable electrically conducting layer, preferentially less than 100 nm, and then in a suitable holder, are electroformed to provide replicas of the original master model surface. It is convenient and economic to use copper as the electroforming metal.

The electroformed watch faces are then finished by applying a further decorative layer to the replica surface, for example of gold in a thin layer of less than 100 nm and various metal finishing operations such as stamping to the final size and machining the rear suface if necessary.

The resultant watch face being made of metal is inherently very stable and the final quality depends essentially upon the care and precision which was exercised in the origination of the initial master model. Only one master model is required for the production of large numbers of identical replicas.

It is of course also possible to use the result of the casting process, a polymer replica of the master model surface, directly as the enhanced surface in the final product. If this course is adopted then the master model must be constructed to be the "negative" of the desired final surface. A suitable decorative finish can then be applied to the surface of the polymer casting, for example a vacuum evaporated gold layer, and final operations such as stamping to size or trimming can be performed. Again, a series of replicas can be made from a single model, but the final result will be less stable both mechanically and thermally than the metal version described above.

The invention described here is not limited to watch faces, but includes metal surfaces where an enhancement is required. As an additional feature the technology described here provides a security feature which can protect the surface of an object into which such a surface is intimately combined, against simulation by conventional printing or engraving methods.

The technology can be applied to costume jewelry to provide product enhancement, to medals and coin-like items where the inclusion of holographic or diffractive -surface elements can provide both enhancement and proof of authenticity, and to general metal objects which can be produced using an electroforming technique and which can be enhanced by the inclusion of holographic and diffractive effects.