The Master of Gemstone Research and Diamond Grading in Korea -Wooshin Gemological Institute of Korea. Launched by the late Mr. Hui-Nam Oh in 1979, Wooshin Gemological Institute of Korea has become the most renowned gemological institute with the largest scale in Korea. WGK has built the basis for gemstone research and a world-class diamond grading system, upgrading the jewelry industry of Korea. As a result, Diamond Grading Report and Colored Stone Identification Report issued by Wooshin Gemological Institute of Korea have become the most trusted and essential cerificates for both sellers and consumers. As the market leader of Korea, WGK is now making a new leap forward to the world stage.