Mediaeval Sinhalese Art c22.75

c22.75

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 an uneven distribution of oxide and sulphide of iron.