Abstract
The so-called pearl essence which causes iridescence of fish scales has long been considered to owe its peculiar optical characteristic to guanin particles contained. This view was confirmed by the result of our experimental research on the pearl essence obtained from the scales of Tachi-u-o or Hair Tail, Trichiurus haumela (Forskål).
The pearl essence loses its lustre when it is either immersed for a long time in formalin or boiled with formalin. This is probably due to the presence of protein.
Some chemical substances such as tyrosin, zinc salt of stearic acid, BaS2O7, PbHCO3, KCIO3, bismuth compounds and MgNH4•PO4, were examined if each of them should be employable as a substitute for the pearl essence. But none of then gave, iridescence.
