Preparation containing: (A) 30 to 90% by weight of at least one organic solvent; (B) 10 to 70% by weight of at least one platinum complex of the type [L1L2Pt[O(CO)R1]X]n, wherein L1 and L2 represent the same or different monoolefin ligands, or together represent a compound L1L2 acting as a diolefin ligand, wherein X is selected from bromide, chloride, iodide, and —O(CO)R2, wherein —O(CO)R1 and —O(CO)R2 represent the same or different C6-C18 non-aromatic monocarboxylic acid groups, or together represent a C8-C18 non-aromatic dicarboxylic acid group —O(CO)R1 R2(CO)O—, wherein they are mononuclear platinum complexes with n=1, or wherein, if L1L2 and/or —O(CO)R1 R2(CO)O— are present, they may be polynuclear platinum complexes with a whole number n>1, and (C) 0 to 10% by weight of at least one additive.