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Tooth blackening in Vietnam was (and still is) a deliberate process. In Vietnam red sticklac, a resin obtained from secretions of an aphid-like insect that sucks the sap of a host tree, is used as a dye. This is diluted with lemon juice or rice alcohol, stored in the dark for a few days and then is applied with pressure to all the teeth. This will then react with an application of iron(mainly from iron nails) or copper from green or black alum and tannin from Chinese gall to give a blue-black color and an insoluble coating. Tooth blackening prevents tooth decay. Those who have had their teeth blackened maintain a full set of teeth longer than those who have not undergone the process. Teeth blackening may prolong life by maintaining the capacity to enjoy a wholesome diet.