The present patent application relates to an aqueous composition comprising: a) at least one compound having general formula (I) and at least one compound having general formula (II), and/or at least one compound having general formula (III) and at least one compound having general formula (IV), wherein R1 and R2, independently of one another, are H or OR5, and R3 and R4, independently of one another, are H or OR5, R5 being an alkyl group or an allyl group; and b) phosphate ions and/or hydrogen phosphate ions and/or condensates thereof.