The mucicarmine technique is used for the demonstration of acid mucins. The active dye molecule is aluminium carminic acid complex known as carmine (Lillie 1977). The exact mechanism is not fully understood but it is believed that aluminium salts form a chelate complex with carminic acid which confers an overall positive charge on the carmine complex attracting sialomucins and sulfomucins and thus staining them whilst neutral mu cins do not stain.