Nantong technical supervision bureau has a gold jewelry testing station, where the certificate is not cheap! Get Koro jewelry from Golden Eagle 14 floor and show it to the proprietress. I haven't received any money, because the proprietress has been making jewelry for more than ten years. She knew at a glance that it was said that she was a diamond grading appraiser more than ten years ago. If you don't want to spend money, go and show it to her. She is very warm and nice!