Method and installation for the vacuum colouring of a metal strip by means of magnetron sputtering

A vacuum process for etching a metal strip running over a backing roll facing a counterelectrode by magnetron sputtering in a vacuum chamber, comprising:

• creating a plasma in a gas close to the metal strip so as to generate radicals and/or ions that act on the strip;
• selecting at least one closed magnetic circuit, the width of which is approximately equal to that of the metal strip, from a series of at least two closed magnetic circuits of different and fixed widths;
• positioning the selected magnetic circuit so as to face the metal strip;
• and
• etching the moving metal strip,
• wherein the at least one magnetic circuit is placed on an outer surface of a cylindrical support placed inside the backing roll concentrically with respect to the backing roll, the cylindrical support being able to rotate about an axis of the cylindrical support.