Etching of copper on a card is achieved by applying an electrical voltage between a cathode (102) and the card (42), the card (42) thereby forming an anode. The cathode (102) and the card (42) are immersed in an electrolyte comprising a first component, which may be reduced from a first state in the form of an ion having a metal atom with a first positive oxidation number to a second state in the form of an ion having said metal atom with a second positive oxidation number, which is less than said first positive oxidation number. A first redox potential in the electrolyte for reduction from the first to the second state is larger than a second redox potential in the electrolyte for reduction of divalent copper ions to metallic copper. During the etching metallic copper on the card is oxidised and transferred into positively charged copper ions while the first component is reduced from its first state to its second state. The quality of the etched structures on the card is improved since no metallic copper is precipitated on the cathode.