The deep interest in innovation of Luis J. Díaz has led him to combine his activity as inventor with his professional career as designer and artistic engraver in the Minting Department of the Royal Mint of Spain (FNMT-RCM) since 1986. Apart from the patents that he has registered himself, he has developed some patents of latent image in coins for the Royal Mint of Spain, a safety measure against counterfeiting of coins that has been implemented not only in Spanish coins but also in foreign ones, such as the current 500 yen one.