228 EIGHTH PACIFIC SCIENCE CONGRESS 



Earnest hopes are attached to these researches in view of the degrading 

 tendency of the quahties of the products due to the recent increase 

 in the number of pearl culture grounds. 



An important aspect of the art of pearl culture is concerned with 

 the scientific evaluation of the quality of a pearl. For this, it is in- 

 dispensable to clarify the essential properties of pearls through physical 

 and chemical approaches. Y. Uchida and M. Ueda made clear the 

 interrelation between the stratiform makeup of the pearl and its 

 irridescence. T. Watanabe is engaged in a research into the interrela- 

 tion between the color and the thickness of a pearl layer and also 

 into the crystallization of the substance. Y. Matsui and T. Hirota have 

 reported that there is a marked difference in the crystalline form be- 

 tween the normal and the baroque pearls. 



Y. Uchida discovered by spectroanalysis that there were remarkable 

 differences in the mineral contents among pearls with different colors. 

 T. Kosaki's report has disclosed that a pearl contains 16-66 /x/lOOg of 

 porphyrin and 5-70 /x/lOOg of metalloporphyrin, varying with the color. 



Recently our laboratory has been made the center of the studies 

 devoted to the discovery of the conditions on which to evaluate the 

 qualities of pearls scientifically. With the help of Hardy's self-record- 

 ing spectrophotometer, T. Fukuda and his collaborators examined 

 pearls with various colors and lusters, and have proved the possibilities 

 of classifying them according to their substantial colors. They have 

 also demonstrated that they can calculate the thickness of the pearl 

 layer by rating the surface color which is formed by the interference of a 

 reflexion. Besides these studies, various other approaches are now be- 

 ing tried to test the pearl as a jewel. 



