Iron in Ancient India c7.s5.t1.6

c7.s5.t1.6

Dr. Kumarswami gives a somewhat different formula used for a long time in Ceylon and even now to give a 'blued' colour to iron articles and also to prevent rusting. The formula runs thus: "Take two parts of alum, one part of copperas, two parts of the leaves of *oxalis corniculata* and grind together and allow to stand three days; add the juice of one lime and spread over the iron to be coloured; place carefully in the fire until the right colour is attained."² Dr. Kumarswami explains the chemical action by supposing that "apparently the oxalic or other organic acid in the preparation reduces any higher oxide of iron to the ferrous state, and when applied to the steel and heated, slight etching takes place and a probable reduction of part of the sulphate to sulphide of iron. The temperature employed would affect the amount of reduction and oxidation. The blue colour is probably due to the uneven distribution of oxide and sulphide of iron."