Coin provided with diffraction structures

A coin (1) having a metal surface (2;

• 3) structured with macroscopic reliefs (5) for the representation of motifs which serve to specify the coin value and as a recognition feature, and fields (10;
• 11;
• 12;
• 14;
• 14′;
• 20) of the surface (2;
• 3), of which at least one has a microscopically fine relief structure (8) with a diffraction action and which form an optically machine-readable identification, characterised in that the relief structures (8) of the identification are selected from M groups of gratings (13), that the grating vectors (79) of all gratings (13) of the M groups are radially oriented, that in each of the M groups the spatial frequency f of the relief structure (8) is selected in dependence on the radial spacing (R) of the field (10;
• 11;
• 12;
• 14;
• 14′;
• 20) from the center point (18) of the coin (1) such that upon illumination of the relief structure (8) by means of a light source (21) in point form arranged perpendicularly above the center point (18), with the wavelength (λ), one of the two partial beams (29;
• 30;
• 84) of the diffracted light crosses the center point (18) at a spacing (hD) which is predetermined for said group.

A method of applying a microscopic relief structure (8) to a comparatively hard material surface (2, 3), characterised by the following steps:

• applying a thin light-sensitive plastic material layer to the material surface (2, 3),
• exposing and developing the plastic material layer so that microscopically fine locations of the material surface (2, 3) are free of plastic material,
• etching the material surface (2, 3), with the microscopic relief structure (8) being formed, and
• removing the plastic material layer.